[movit] / effect_chain.cpp

#define GL_GLEXT_PROTOTYPES 1

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <assert.h>
#include <GL/glew.h>

#include <algorithm>
#include <set>
#include <stack>
#include <vector>

#include "util.h"
#include "effect_chain.h"
#include "gamma_expansion_effect.h"
#include "gamma_compression_effect.h"
#include "colorspace_conversion_effect.h"
#include "dither_effect.h"
#include "input.h"
#include "init.h"

EffectChain::EffectChain(float aspect_nom, float aspect_denom)
        : aspect_nom(aspect_nom),
          aspect_denom(aspect_denom),
          dither_effect(NULL),
          fbo(0),
          num_dither_bits(0),
          finalized(false) {}

EffectChain::~EffectChain()
{
        for (unsigned i = 0; i < nodes.size(); ++i) {
                if (nodes[i]->output_texture != 0) {
                        glDeleteTextures(1, &nodes[i]->output_texture);
                }
                delete nodes[i]->effect;
                delete nodes[i];
        }
        for (unsigned i = 0; i < phases.size(); ++i) {
                glDeleteProgram(phases[i]->glsl_program_num);
                glDeleteShader(phases[i]->vertex_shader);
                glDeleteShader(phases[i]->fragment_shader);
                delete phases[i];
        }
        if (fbo != 0) {
                glDeleteFramebuffers(1, &fbo);
        }
}

Input *EffectChain::add_input(Input *input)
{
        inputs.push_back(input);
        add_node(input);
        return input;
}

void EffectChain::add_output(const ImageFormat &format)
{
        output_format = format;
}

Node *EffectChain::add_node(Effect *effect)
{
        char effect_id[256];
        sprintf(effect_id, "eff%u", (unsigned)nodes.size());

        Node *node = new Node;
        node->effect = effect;
        node->disabled = false;
        node->effect_id = effect_id;
        node->output_color_space = COLORSPACE_INVALID;
        node->output_gamma_curve = GAMMA_INVALID;
        node->output_texture = 0;

        nodes.push_back(node);
        node_map[effect] = node;
        return node;
}

void EffectChain::connect_nodes(Node *sender, Node *receiver)
{
        sender->outgoing_links.push_back(receiver);
        receiver->incoming_links.push_back(sender);
}

void EffectChain::replace_receiver(Node *old_receiver, Node *new_receiver)
{
        new_receiver->incoming_links = old_receiver->incoming_links;
        old_receiver->incoming_links.clear();
        
        for (unsigned i = 0; i < new_receiver->incoming_links.size(); ++i) {
                Node *sender = new_receiver->incoming_links[i];
                for (unsigned j = 0; j < sender->outgoing_links.size(); ++j) {
                        if (sender->outgoing_links[j] == old_receiver) {
                                sender->outgoing_links[j] = new_receiver;
                        }
                }
        }       
}

void EffectChain::replace_sender(Node *old_sender, Node *new_sender)
{
        new_sender->outgoing_links = old_sender->outgoing_links;
        old_sender->outgoing_links.clear();
        
        for (unsigned i = 0; i < new_sender->outgoing_links.size(); ++i) {
                Node *receiver = new_sender->outgoing_links[i];
                for (unsigned j = 0; j < receiver->incoming_links.size(); ++j) {
                        if (receiver->incoming_links[j] == old_sender) {
                                receiver->incoming_links[j] = new_sender;
                        }
                }
        }       
}

void EffectChain::insert_node_between(Node *sender, Node *middle, Node *receiver)
{
        for (unsigned i = 0; i < sender->outgoing_links.size(); ++i) {
                if (sender->outgoing_links[i] == receiver) {
                        sender->outgoing_links[i] = middle;
                        middle->incoming_links.push_back(sender);
                }
        }
        for (unsigned i = 0; i < receiver->incoming_links.size(); ++i) {
                if (receiver->incoming_links[i] == sender) {
                        receiver->incoming_links[i] = middle;
                        middle->outgoing_links.push_back(receiver);
                }
        }

        assert(middle->incoming_links.size() == middle->effect->num_inputs());
}

void EffectChain::find_all_nonlinear_inputs(Node *node, std::vector<Node *> *nonlinear_inputs)
{
        if (node->output_gamma_curve == GAMMA_LINEAR &&
            node->effect->effect_type_id() != "GammaCompressionEffect") {
                return;
        }
        if (node->effect->num_inputs() == 0) {
                nonlinear_inputs->push_back(node);
        } else {
                assert(node->effect->num_inputs() == node->incoming_links.size());
                for (unsigned i = 0; i < node->incoming_links.size(); ++i) {
                        find_all_nonlinear_inputs(node->incoming_links[i], nonlinear_inputs);
                }
        }
}

Effect *EffectChain::add_effect(Effect *effect, const std::vector<Effect *> &inputs)
{
        assert(inputs.size() == effect->num_inputs());
        Node *node = add_node(effect);
        for (unsigned i = 0; i < inputs.size(); ++i) {
                assert(node_map.count(inputs[i]) != 0);
                connect_nodes(node_map[inputs[i]], node);
        }
        return effect;
}

// GLSL pre-1.30 doesn't support token pasting. Replace PREFIX(x) with <effect_id>_x.
std::string replace_prefix(const std::string &text, const std::string &prefix)
{
        std::string output;
        size_t start = 0;

        while (start < text.size()) {
                size_t pos = text.find("PREFIX(", start);
                if (pos == std::string::npos) {
                        output.append(text.substr(start, std::string::npos));
                        break;
                }

                output.append(text.substr(start, pos - start));
                output.append(prefix);
                output.append("_");

                pos += strlen("PREFIX(");
        
                // Output stuff until we find the matching ), which we then eat.
                int depth = 1;
                size_t end_arg_pos = pos;
                while (end_arg_pos < text.size()) {
                        if (text[end_arg_pos] == '(') {
                                ++depth;
                        } else if (text[end_arg_pos] == ')') {
                                --depth;
                                if (depth == 0) {
                                        break;
                                }
                        }
                        ++end_arg_pos;
                }
                output.append(text.substr(pos, end_arg_pos - pos));
                ++end_arg_pos;
                assert(depth == 0);
                start = end_arg_pos;
        }
        return output;
}

Phase *EffectChain::compile_glsl_program(
        const std::vector<Node *> &inputs,
        const std::vector<Node *> &effects)
{
        assert(!effects.empty());

        // Deduplicate the inputs.
        std::vector<Node *> true_inputs = inputs;
        std::sort(true_inputs.begin(), true_inputs.end());
        true_inputs.erase(std::unique(true_inputs.begin(), true_inputs.end()), true_inputs.end());

        bool input_needs_mipmaps = false;
        std::string frag_shader = read_file("header.frag");

        // Create functions for all the texture inputs that we need.
        for (unsigned i = 0; i < true_inputs.size(); ++i) {
                Node *input = true_inputs[i];
        
                frag_shader += std::string("uniform sampler2D tex_") + input->effect_id + ";\n";
                frag_shader += std::string("vec4 ") + input->effect_id + "(vec2 tc) {\n";
                frag_shader += "\treturn texture2D(tex_" + input->effect_id + ", tc);\n";
                frag_shader += "}\n";
                frag_shader += "\n";
        }

        for (unsigned i = 0; i < effects.size(); ++i) {
                Node *node = effects[i];

                if (node->incoming_links.size() == 1) {
                        frag_shader += std::string("#define INPUT ") + node->incoming_links[0]->effect_id + "\n";
                } else {
                        for (unsigned j = 0; j < node->incoming_links.size(); ++j) {
                                char buf[256];
                                sprintf(buf, "#define INPUT%d %s\n", j + 1, node->incoming_links[j]->effect_id.c_str());
                                frag_shader += buf;
                        }
                }
        
                frag_shader += "\n";
                frag_shader += std::string("#define FUNCNAME ") + node->effect_id + "\n";
                frag_shader += replace_prefix(node->effect->output_convenience_uniforms(), node->effect_id);
                frag_shader += replace_prefix(node->effect->output_fragment_shader(), node->effect_id);
                frag_shader += "#undef PREFIX\n";
                frag_shader += "#undef FUNCNAME\n";
                if (node->incoming_links.size() == 1) {
                        frag_shader += "#undef INPUT\n";
                } else {
                        for (unsigned j = 0; j < node->incoming_links.size(); ++j) {
                                char buf[256];
                                sprintf(buf, "#undef INPUT%d\n", j + 1);
                                frag_shader += buf;
                        }
                }
                frag_shader += "\n";

                input_needs_mipmaps |= node->effect->needs_mipmaps();
        }
        for (unsigned i = 0; i < effects.size(); ++i) {
                Node *node = effects[i];
                if (node->effect->num_inputs() == 0) {
                        CHECK(node->effect->set_int("needs_mipmaps", input_needs_mipmaps));
                }
        }
        frag_shader += std::string("#define INPUT ") + effects.back()->effect_id + "\n";
        frag_shader.append(read_file("footer.frag"));

        if (movit_debug_level == MOVIT_DEBUG_ON) {
                // Output shader to a temporary file, for easier debugging.
                static int compiled_shader_num = 0;
                char filename[256];
                sprintf(filename, "chain-%03d.frag", compiled_shader_num++);
                FILE *fp = fopen(filename, "w");
                if (fp == NULL) {
                        perror(filename);
                        exit(1);
                }
                fprintf(fp, "%s\n", frag_shader.c_str());
                fclose(fp);
        }
        
        GLuint glsl_program_num = glCreateProgram();
        GLuint vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
        GLuint fs_obj = compile_shader(frag_shader, GL_FRAGMENT_SHADER);
        glAttachShader(glsl_program_num, vs_obj);
        check_error();
        glAttachShader(glsl_program_num, fs_obj);
        check_error();
        glLinkProgram(glsl_program_num);
        check_error();

        Phase *phase = new Phase;
        phase->glsl_program_num = glsl_program_num;
        phase->vertex_shader = vs_obj;
        phase->fragment_shader = fs_obj;
        phase->input_needs_mipmaps = input_needs_mipmaps;
        phase->inputs = true_inputs;
        phase->effects = effects;

        return phase;
}

// Construct GLSL programs, starting at the given effect and following
// the chain from there. We end a program every time we come to an effect
// marked as "needs texture bounce", one that is used by multiple other
// effects, every time an effect wants to change the output size,
// and of course at the end.
//
// We follow a quite simple depth-first search from the output, although
// without any explicit recursion.
void EffectChain::construct_glsl_programs(Node *output)
{
        // Which effects have already been completed in this phase?
        // We need to keep track of it, as an effect with multiple outputs
        // could otherwise be calculate multiple times.
        std::set<Node *> completed_effects;

        // Effects in the current phase, as well as inputs (outputs from other phases
        // that we depend on). Note that since we start iterating from the end,
        // the effect list will be in the reverse order.
        std::vector<Node *> this_phase_inputs;
        std::vector<Node *> this_phase_effects;

        // Effects that we have yet to calculate, but that we know should
        // be in the current phase.
        std::stack<Node *> effects_todo_this_phase;

        // Effects that we have yet to calculate, but that come from other phases.
        // We delay these until we have this phase done in its entirety,
        // at which point we pick any of them and start a new phase from that.
        std::stack<Node *> effects_todo_other_phases;

        effects_todo_this_phase.push(output);

        for ( ;; ) {  // Termination condition within loop.
                if (!effects_todo_this_phase.empty()) {
                        // OK, we have more to do this phase.
                        Node *node = effects_todo_this_phase.top();
                        effects_todo_this_phase.pop();

                        // This should currently only happen for effects that are phase outputs,
                        // and we throw those out separately below.
                        assert(completed_effects.count(node) == 0);

                        this_phase_effects.push_back(node);
                        completed_effects.insert(node);

                        // Find all the dependencies of this effect, and add them to the stack.
                        std::vector<Node *> deps = node->incoming_links;
                        assert(node->effect->num_inputs() == deps.size());
                        for (unsigned i = 0; i < deps.size(); ++i) {
                                bool start_new_phase = false;

                                // FIXME: If we sample directly from a texture, we won't need this.
                                if (node->effect->needs_texture_bounce()) {
                                        start_new_phase = true;
                                }

                                if (deps[i]->outgoing_links.size() > 1) {
                                        if (deps[i]->effect->num_inputs() > 0) {
                                                // More than one effect uses this as the input,
                                                // and it is not a texture itself.
                                                // The easiest thing to do (and probably also the safest
                                                // performance-wise in most cases) is to bounce it to a texture
                                                // and then let the next passes read from that.
                                                start_new_phase = true;
                                        } else {
                                                // For textures, we try to be slightly more clever;
                                                // if none of our outputs need a bounce, we don't bounce
                                                // but instead simply use the effect many times.
                                                //
                                                // Strictly speaking, we could bounce it for some outputs
                                                // and use it directly for others, but the processing becomes
                                                // somewhat simpler if the effect is only used in one such way.
                                                for (unsigned j = 0; j < deps[i]->outgoing_links.size(); ++j) {
                                                        Node *rdep = deps[i]->outgoing_links[j];
                                                        start_new_phase |= rdep->effect->needs_texture_bounce();
                                                }
                                        }
                                }

                                if (deps[i]->effect->changes_output_size()) {
                                        start_new_phase = true;
                                }

                                if (start_new_phase) {
                                        effects_todo_other_phases.push(deps[i]);
                                        this_phase_inputs.push_back(deps[i]);
                                } else {
                                        effects_todo_this_phase.push(deps[i]);
                                }
                        }
                        continue;
                }

                // No more effects to do this phase. Take all the ones we have,
                // and create a GLSL program for it.
                if (!this_phase_effects.empty()) {
                        reverse(this_phase_effects.begin(), this_phase_effects.end());
                        phases.push_back(compile_glsl_program(this_phase_inputs, this_phase_effects));
                        this_phase_effects.back()->phase = phases.back();
                        this_phase_inputs.clear();
                        this_phase_effects.clear();
                }
                assert(this_phase_inputs.empty());
                assert(this_phase_effects.empty());

                // If we have no effects left, exit.
                if (effects_todo_other_phases.empty()) {
                        break;
                }

                Node *node = effects_todo_other_phases.top();
                effects_todo_other_phases.pop();

                if (completed_effects.count(node) == 0) {
                        // Start a new phase, calculating from this effect.
                        effects_todo_this_phase.push(node);
                }
        }

        // Finally, since the phases are found from the output but must be executed
        // from the input(s), reverse them, too.
        std::reverse(phases.begin(), phases.end());
}

void EffectChain::output_dot(const char *filename)
{
        if (movit_debug_level != MOVIT_DEBUG_ON) {
                return;
        }

        FILE *fp = fopen(filename, "w");
        if (fp == NULL) {
                perror(filename);
                exit(1);
        }

        fprintf(fp, "digraph G {\n");
        for (unsigned i = 0; i < nodes.size(); ++i) {
                // Find out which phase this event belongs to.
                int in_phase = -1;
                for (unsigned j = 0; j < phases.size(); ++j) {
                        const Phase* p = phases[j];
                        if (std::find(p->effects.begin(), p->effects.end(), nodes[i]) != p->effects.end()) {
                                assert(in_phase == -1);
                                in_phase = j;
                        }
                }

                if (in_phase == -1) {
                        fprintf(fp, "  n%ld [label=\"%s\"];\n", (long)nodes[i], nodes[i]->effect->effect_type_id().c_str());
                } else {
                        fprintf(fp, "  n%ld [label=\"%s\" style=\"filled\" fillcolor=\"/accent8/%d\"];\n",
                                (long)nodes[i], nodes[i]->effect->effect_type_id().c_str(),
                                (in_phase % 8) + 1);
                }
                for (unsigned j = 0; j < nodes[i]->outgoing_links.size(); ++j) {
                        std::vector<std::string> labels;

                        if (nodes[i]->outgoing_links[j]->effect->needs_texture_bounce()) {
                                labels.push_back("needs_bounce");
                        }
                        if (nodes[i]->effect->changes_output_size()) {
                                labels.push_back("resize");
                        }

                        switch (nodes[i]->output_color_space) {
                        case COLORSPACE_INVALID:
                                labels.push_back("spc[invalid]");
                                break;
                        case COLORSPACE_REC_601_525:
                                labels.push_back("spc[rec601-525]");
                                break;
                        case COLORSPACE_REC_601_625:
                                labels.push_back("spc[rec601-625]");
                                break;
                        default:
                                break;
                        }

                        switch (nodes[i]->output_gamma_curve) {
                        case GAMMA_INVALID:
                                labels.push_back("gamma[invalid]");
                                break;
                        case GAMMA_sRGB:
                                labels.push_back("gamma[sRGB]");
                                break;
                        case GAMMA_REC_601:  // and GAMMA_REC_709
                                labels.push_back("gamma[rec601/709]");
                                break;
                        default:
                                break;
                        }

                        if (labels.empty()) {
                                fprintf(fp, "  n%ld -> n%ld;\n", (long)nodes[i], (long)nodes[i]->outgoing_links[j]);
                        } else {
                                std::string label = labels[0];
                                for (unsigned k = 1; k < labels.size(); ++k) {
                                        label += ", " + labels[k];
                                }
                                fprintf(fp, "  n%ld -> n%ld [label=\"%s\"];\n", (long)nodes[i], (long)nodes[i]->outgoing_links[j], label.c_str());
                        }
                }
        }
        fprintf(fp, "}\n");

        fclose(fp);
}

unsigned EffectChain::fit_rectangle_to_aspect(unsigned width, unsigned height)
{
        if (float(width) * aspect_denom >= float(height) * aspect_nom) {
                // Same aspect, or W/H > aspect (image is wider than the frame).
                // In either case, keep width.
                return width;
        } else {
                // W/H < aspect (image is taller than the frame), so keep height,
                // and adjust width correspondingly.
                return lrintf(height * aspect_nom / aspect_denom);
        }
}

// Propagate input texture sizes throughout, and inform effects downstream.
// (Like a lot of other code, we depend on effects being in topological order.)
void EffectChain::inform_input_sizes(Phase *phase)
{
        // All effects that have a defined size (inputs and RTT inputs)
        // get that. Reset all others.
        for (unsigned i = 0; i < phase->effects.size(); ++i) {
                Node *node = phase->effects[i];
                if (node->effect->num_inputs() == 0) {
                        Input *input = static_cast<Input *>(node->effect);
                        node->output_width = input->get_width();
                        node->output_height = input->get_height();
                        assert(node->output_width != 0);
                        assert(node->output_height != 0);
                } else {
                        node->output_width = node->output_height = 0;
                }
        }
        for (unsigned i = 0; i < phase->inputs.size(); ++i) {
                Node *input = phase->inputs[i];
                input->output_width = input->phase->output_width;
                input->output_height = input->phase->output_height;
                assert(input->output_width != 0);
                assert(input->output_height != 0);
        }

        // Now propagate from the inputs towards the end, and inform as we go.
        // The rules are simple:
        //
        //   1. Don't touch effects that already have given sizes (ie., inputs).
        //   2. If all of your inputs have the same size, that will be your output size.
        //   3. Otherwise, your output size is 0x0.
        for (unsigned i = 0; i < phase->effects.size(); ++i) {
                Node *node = phase->effects[i];
                if (node->effect->num_inputs() == 0) {
                        continue;
                }
                unsigned this_output_width = 0;
                unsigned this_output_height = 0;
                for (unsigned j = 0; j < node->incoming_links.size(); ++j) {
                        Node *input = node->incoming_links[j];
                        node->effect->inform_input_size(j, input->output_width, input->output_height);
                        if (j == 0) {
                                this_output_width = input->output_width;
                                this_output_height = input->output_height;
                        } else if (input->output_width != this_output_width || input->output_height != this_output_height) {
                                // Inputs disagree.
                                this_output_width = 0;
                                this_output_height = 0;
                        }
                }
                node->output_width = this_output_width;
                node->output_height = this_output_height;
        }
}

// Note: You should call inform_input_sizes() before this, as the last effect's
// desired output size might change based on the inputs.
void EffectChain::find_output_size(Phase *phase)
{
        Node *output_node = phase->effects.back();

        // If the last effect explicitly sets an output size, use that.
        if (output_node->effect->changes_output_size()) {
                output_node->effect->get_output_size(&phase->output_width, &phase->output_height);
                return;
        }

        // If not, look at the input phases and textures.
        // We select the largest one (by fit into the current aspect).
        unsigned best_width = 0;
        for (unsigned i = 0; i < phase->inputs.size(); ++i) {
                Node *input = phase->inputs[i];
                assert(input->phase->output_width != 0);
                assert(input->phase->output_height != 0);
                unsigned width = fit_rectangle_to_aspect(input->phase->output_width, input->phase->output_height);
                if (width > best_width) {
                        best_width = width;
                }
        }
        for (unsigned i = 0; i < phase->effects.size(); ++i) {
                Effect *effect = phase->effects[i]->effect;
                if (effect->num_inputs() != 0) {
                        continue;
                }

                Input *input = static_cast<Input *>(effect);
                unsigned width = fit_rectangle_to_aspect(input->get_width(), input->get_height());
                if (width > best_width) {
                        best_width = width;
                }
        }
        assert(best_width != 0);
        phase->output_width = best_width;
        phase->output_height = best_width * aspect_denom / aspect_nom;
}

void EffectChain::sort_nodes_topologically()
{
        std::set<Node *> visited_nodes;
        std::vector<Node *> sorted_list;
        for (unsigned i = 0; i < nodes.size(); ++i) {
                if (nodes[i]->incoming_links.size() == 0) {
                        topological_sort_visit_node(nodes[i], &visited_nodes, &sorted_list);
                }
        }
        reverse(sorted_list.begin(), sorted_list.end());
        nodes = sorted_list;
}

void EffectChain::topological_sort_visit_node(Node *node, std::set<Node *> *visited_nodes, std::vector<Node *> *sorted_list)
{
        if (visited_nodes->count(node) != 0) {
                return;
        }
        visited_nodes->insert(node);
        for (unsigned i = 0; i < node->outgoing_links.size(); ++i) {
                topological_sort_visit_node(node->outgoing_links[i], visited_nodes, sorted_list);
        }
        sorted_list->push_back(node);
}

void EffectChain::find_color_spaces_for_inputs()
{
        for (unsigned i = 0; i < nodes.size(); ++i) {
                Node *node = nodes[i];
                if (node->disabled) {
                        continue;
                }
                if (node->incoming_links.size() == 0) {
                        Input *input = static_cast<Input *>(node->effect);
                        node->output_color_space = input->get_color_space();
                        node->output_gamma_curve = input->get_gamma_curve();
                }
        }
}

// Propagate gamma and color space information as far as we can in the graph.
// The rules are simple: Anything where all the inputs agree, get that as
// output as well. Anything else keeps having *_INVALID.
void EffectChain::propagate_gamma_and_color_space()
{
        // We depend on going through the nodes in order.
        sort_nodes_topologically();

        for (unsigned i = 0; i < nodes.size(); ++i) {
                Node *node = nodes[i];
                if (node->disabled) {
                        continue;
                }
                assert(node->incoming_links.size() == node->effect->num_inputs());
                if (node->incoming_links.size() == 0) {
                        assert(node->output_color_space != COLORSPACE_INVALID);
                        assert(node->output_gamma_curve != GAMMA_INVALID);
                        continue;
                }

                Colorspace color_space = node->incoming_links[0]->output_color_space;
                GammaCurve gamma_curve = node->incoming_links[0]->output_gamma_curve;
                for (unsigned j = 1; j < node->incoming_links.size(); ++j) {
                        if (node->incoming_links[j]->output_color_space != color_space) {
                                color_space = COLORSPACE_INVALID;
                        }
                        if (node->incoming_links[j]->output_gamma_curve != gamma_curve) {
                                gamma_curve = GAMMA_INVALID;
                        }
                }

                // The conversion effects already have their outputs set correctly,
                // so leave them alone.
                if (node->effect->effect_type_id() != "ColorspaceConversionEffect") {
                        node->output_color_space = color_space;
                }               
                if (node->effect->effect_type_id() != "GammaCompressionEffect" &&
                    node->effect->effect_type_id() != "GammaExpansionEffect") {
                        node->output_gamma_curve = gamma_curve;
                }               
        }
}

bool EffectChain::node_needs_colorspace_fix(Node *node)
{
        if (node->disabled) {
                return false;
        }
        if (node->effect->num_inputs() == 0) {
                return false;
        }

        // propagate_gamma_and_color_space() has already set our output
        // to COLORSPACE_INVALID if the inputs differ, so we can rely on that.
        if (node->output_color_space == COLORSPACE_INVALID) {
                return true;
        }
        return (node->effect->needs_srgb_primaries() && node->output_color_space != COLORSPACE_sRGB);
}

// Fix up color spaces so that there are no COLORSPACE_INVALID nodes left in
// the graph. Our strategy is not always optimal, but quite simple:
// Find an effect that's as early as possible where the inputs are of
// unacceptable colorspaces (that is, either different, or, if the effect only
// wants sRGB, not sRGB.) Add appropriate conversions on all its inputs,
// propagate the information anew, and repeat until there are no more such
// effects.
void EffectChain::fix_internal_color_spaces()
{
        unsigned colorspace_propagation_pass = 0;
        bool found_any;
        do {
                found_any = false;
                for (unsigned i = 0; i < nodes.size(); ++i) {
                        Node *node = nodes[i];
                        if (!node_needs_colorspace_fix(node)) {
                                continue;
                        }

                        // Go through each input that is not sRGB, and insert
                        // a colorspace conversion before it.
                        for (unsigned j = 0; j < node->incoming_links.size(); ++j) {
                                Node *input = node->incoming_links[j];
                                assert(input->output_color_space != COLORSPACE_INVALID);
                                if (input->output_color_space == COLORSPACE_sRGB) {
                                        continue;
                                }
                                Node *conversion = add_node(new ColorspaceConversionEffect());
                                CHECK(conversion->effect->set_int("source_space", input->output_color_space));
                                CHECK(conversion->effect->set_int("destination_space", COLORSPACE_sRGB));
                                conversion->output_color_space = COLORSPACE_sRGB;
                                insert_node_between(input, conversion, node);
                        }

                        // Re-sort topologically, and propagate the new information.
                        propagate_gamma_and_color_space();
                        
                        found_any = true;
                        break;
                }
        
                char filename[256];
                sprintf(filename, "step3-colorspacefix-iter%u.dot", ++colorspace_propagation_pass);
                output_dot(filename);
                assert(colorspace_propagation_pass < 100);
        } while (found_any);

        for (unsigned i = 0; i < nodes.size(); ++i) {
                Node *node = nodes[i];
                if (node->disabled) {
                        continue;
                }
                assert(node->output_color_space != COLORSPACE_INVALID);
        }
}

// Make so that the output is in the desired color space.
void EffectChain::fix_output_color_space()
{
        Node *output = find_output_node();
        if (output->output_color_space != output_format.color_space) {
                Node *conversion = add_node(new ColorspaceConversionEffect());
                CHECK(conversion->effect->set_int("source_space", output->output_color_space));
                CHECK(conversion->effect->set_int("destination_space", output_format.color_space));
                conversion->output_color_space = output_format.color_space;
                connect_nodes(output, conversion);
                propagate_gamma_and_color_space();
        }
}

bool EffectChain::node_needs_gamma_fix(Node *node)
{
        if (node->disabled) {
                return false;
        }

        // Small hack since the output is not an explicit node:
        // If we are the last node and our output is in the wrong
        // space compared to EffectChain's output, we need to fix it.
        // This will only take us to linear, but fix_output_gamma()
        // will come and take us to the desired output gamma
        // if it is needed.
        //
        // This needs to be before everything else, since it could
        // even apply to inputs (if they are the only effect).
        if (node->outgoing_links.empty() &&
            node->output_gamma_curve != output_format.gamma_curve &&
            node->output_gamma_curve != GAMMA_LINEAR) {
                return true;
        }

        if (node->effect->num_inputs() == 0) {
                return false;
        }

        // propagate_gamma_and_color_space() has already set our output
        // to GAMMA_INVALID if the inputs differ, so we can rely on that,
        // except for GammaCompressionEffect.
        if (node->output_gamma_curve == GAMMA_INVALID) {
                return true;
        }
        if (node->effect->effect_type_id() == "GammaCompressionEffect") {
                assert(node->incoming_links.size() == 1);
                return node->incoming_links[0]->output_gamma_curve != GAMMA_LINEAR;
        }

        return (node->effect->needs_linear_light() && node->output_gamma_curve != GAMMA_LINEAR);
}

// Very similar to fix_internal_color_spaces(), but for gamma.
// There is one difference, though; before we start adding conversion nodes,
// we see if we can get anything out of asking the sources to deliver
// linear gamma directly. fix_internal_gamma_by_asking_inputs()
// does that part, while fix_internal_gamma_by_inserting_nodes()
// inserts nodes as needed afterwards.
void EffectChain::fix_internal_gamma_by_asking_inputs(unsigned step)
{
        unsigned gamma_propagation_pass = 0;
        bool found_any;
        do {
                found_any = false;
                for (unsigned i = 0; i < nodes.size(); ++i) {
                        Node *node = nodes[i];
                        if (!node_needs_gamma_fix(node)) {
                                continue;
                        }

                        // See if all inputs can give us linear gamma. If not, leave it.
                        std::vector<Node *> nonlinear_inputs;
                        find_all_nonlinear_inputs(node, &nonlinear_inputs);
                        assert(!nonlinear_inputs.empty());

                        bool all_ok = true;
                        for (unsigned i = 0; i < nonlinear_inputs.size(); ++i) {
                                Input *input = static_cast<Input *>(nonlinear_inputs[i]->effect);
                                all_ok &= input->can_output_linear_gamma();
                        }

                        if (!all_ok) {
                                continue;
                        }

                        for (unsigned i = 0; i < nonlinear_inputs.size(); ++i) {
                                CHECK(nonlinear_inputs[i]->effect->set_int("output_linear_gamma", 1));
                                nonlinear_inputs[i]->output_gamma_curve = GAMMA_LINEAR;
                        }

                        // Re-sort topologically, and propagate the new information.
                        propagate_gamma_and_color_space();
                        
                        found_any = true;
                        break;
                }
        
                char filename[256];
                sprintf(filename, "step%u-gammafix-iter%u.dot", step, ++gamma_propagation_pass);
                output_dot(filename);
                assert(gamma_propagation_pass < 100);
        } while (found_any);
}

void EffectChain::fix_internal_gamma_by_inserting_nodes(unsigned step)
{
        unsigned gamma_propagation_pass = 0;
        bool found_any;
        do {
                found_any = false;
                for (unsigned i = 0; i < nodes.size(); ++i) {
                        Node *node = nodes[i];
                        if (!node_needs_gamma_fix(node)) {
                                continue;
                        }

                        // Special case: We could be an input and still be asked to
                        // fix our gamma; if so, we should be the only node
                        // (as node_needs_gamma_fix() would only return true in
                        // for an input in that case). That means we should insert
                        // a conversion node _after_ ourselves.
                        if (node->incoming_links.empty()) {
                                assert(node->outgoing_links.empty());
                                Node *conversion = add_node(new GammaExpansionEffect());
                                CHECK(conversion->effect->set_int("source_curve", node->output_gamma_curve));
                                conversion->output_gamma_curve = GAMMA_LINEAR;
                                connect_nodes(node, conversion);
                        }

                        // If not, go through each input that is not linear gamma,
                        // and insert a gamma conversion before it.
                        for (unsigned j = 0; j < node->incoming_links.size(); ++j) {
                                Node *input = node->incoming_links[j];
                                assert(input->output_gamma_curve != GAMMA_INVALID);
                                if (input->output_gamma_curve == GAMMA_LINEAR) {
                                        continue;
                                }
                                Node *conversion = add_node(new GammaExpansionEffect());
                                CHECK(conversion->effect->set_int("source_curve", input->output_gamma_curve));
                                conversion->output_gamma_curve = GAMMA_LINEAR;
                                insert_node_between(input, conversion, node);
                        }

                        // Re-sort topologically, and propagate the new information.
                        propagate_gamma_and_color_space();
                        
                        found_any = true;
                        break;
                }
        
                char filename[256];
                sprintf(filename, "step%u-gammafix-iter%u.dot", step, ++gamma_propagation_pass);
                output_dot(filename);
                assert(gamma_propagation_pass < 100);
        } while (found_any);

        for (unsigned i = 0; i < nodes.size(); ++i) {
                Node *node = nodes[i];
                if (node->disabled) {
                        continue;
                }
                assert(node->output_gamma_curve != GAMMA_INVALID);
        }
}

// Make so that the output is in the desired gamma.
// Note that this assumes linear input gamma, so it might create the need
// for another pass of fix_internal_gamma().
void EffectChain::fix_output_gamma()
{
        Node *output = find_output_node();
        if (output->output_gamma_curve != output_format.gamma_curve) {
                Node *conversion = add_node(new GammaCompressionEffect());
                CHECK(conversion->effect->set_int("destination_curve", output_format.gamma_curve));
                conversion->output_gamma_curve = output_format.gamma_curve;
                connect_nodes(output, conversion);
        }
}
        
// If the user has requested dither, add a DitherEffect right at the end
// (after GammaCompressionEffect etc.). This needs to be done after everything else,
// since dither is about the only effect that can _not_ be done in linear space.
void EffectChain::add_dither_if_needed()
{
        if (num_dither_bits == 0) {
                return;
        }
        Node *output = find_output_node();
        Node *dither = add_node(new DitherEffect());
        CHECK(dither->effect->set_int("num_bits", num_dither_bits));
        connect_nodes(output, dither);

        dither_effect = dither->effect;
}

// Find the output node. This is, simply, one that has no outgoing links.
// If there are multiple ones, the graph is malformed (we do not support
// multiple outputs right now).
Node *EffectChain::find_output_node()
{
        std::vector<Node *> output_nodes;
        for (unsigned i = 0; i < nodes.size(); ++i) {
                Node *node = nodes[i];
                if (node->disabled) {
                        continue;
                }
                if (node->outgoing_links.empty()) {
                        output_nodes.push_back(node);
                }
        }
        assert(output_nodes.size() == 1);
        return output_nodes[0];
}

void EffectChain::finalize()
{
        // Output the graph as it is before we do any conversions on it.
        output_dot("step0-start.dot");

        // Give each effect in turn a chance to rewrite its own part of the graph.
        // Note that if more effects are added as part of this, they will be
        // picked up as part of the same for loop, since they are added at the end.
        for (unsigned i = 0; i < nodes.size(); ++i) {
                nodes[i]->effect->rewrite_graph(this, nodes[i]);
        }
        output_dot("step1-rewritten.dot");

        find_color_spaces_for_inputs();
        output_dot("step2-propagated.dot");

        propagate_gamma_and_color_space();
        output_dot("step3-propagated.dot");

        fix_internal_color_spaces();
        fix_output_color_space();
        output_dot("step4-output-colorspacefix.dot");

        // Note that we need to fix gamma after colorspace conversion,
        // because colorspace conversions might create needs for gamma conversions.
        // Also, we need to run an extra pass of fix_internal_gamma() after 
        // fixing the output gamma, as we only have conversions to/from linear.
        fix_internal_gamma_by_asking_inputs(5);
        fix_internal_gamma_by_inserting_nodes(6);
        fix_output_gamma();
        output_dot("step7-output-gammafix.dot");
        fix_internal_gamma_by_asking_inputs(8);
        fix_internal_gamma_by_inserting_nodes(9);

        output_dot("step10-before-dither.dot");

        add_dither_if_needed();

        output_dot("step11-final.dot");
        
        // Construct all needed GLSL programs, starting at the output.
        construct_glsl_programs(find_output_node());

        output_dot("step12-split-to-phases.dot");

        // If we have more than one phase, we need intermediate render-to-texture.
        // Construct an FBO, and then as many textures as we need.
        // We choose the simplest option of having one texture per output,
        // since otherwise this turns into an (albeit simple)
        // register allocation problem.
        if (phases.size() > 1) {
                glGenFramebuffers(1, &fbo);

                for (unsigned i = 0; i < phases.size() - 1; ++i) {
                        inform_input_sizes(phases[i]);
                        find_output_size(phases[i]);

                        Node *output_node = phases[i]->effects.back();
                        glGenTextures(1, &output_node->output_texture);
                        check_error();
                        glBindTexture(GL_TEXTURE_2D, output_node->output_texture);
                        check_error();
                        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
                        check_error();
                        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
                        check_error();
                        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F_ARB, phases[i]->output_width, phases[i]->output_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
                        check_error();

                        output_node->output_texture_width = phases[i]->output_width;
                        output_node->output_texture_height = phases[i]->output_height;
                }
                inform_input_sizes(phases.back());
        }
                
        for (unsigned i = 0; i < inputs.size(); ++i) {
                inputs[i]->finalize();
        }

        assert(phases[0]->inputs.empty());
        
        finalized = true;
}

void EffectChain::render_to_fbo(GLuint dest_fbo, unsigned width, unsigned height)
{
        assert(finalized);

        // Save original viewport.
        GLuint x = 0, y = 0;

        if (width == 0 && height == 0) {
                GLint viewport[4];
                glGetIntegerv(GL_VIEWPORT, viewport);
                x = viewport[0];
                y = viewport[1];
                width = viewport[2];
                height = viewport[3];
        }

        // Basic state.
        glDisable(GL_BLEND);
        check_error();
        glDisable(GL_DEPTH_TEST);
        check_error();
        glDepthMask(GL_FALSE);
        check_error();

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0.0, 1.0, 0.0, 1.0, 0.0, 1.0);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        if (phases.size() > 1) {
                glBindFramebuffer(GL_FRAMEBUFFER, fbo);
                check_error();
        }

        std::set<Node *> generated_mipmaps;

        for (unsigned phase = 0; phase < phases.size(); ++phase) {
                // See if the requested output size has changed. If so, we need to recreate
                // the texture (and before we start setting up inputs).
                inform_input_sizes(phases[phase]);
                if (phase != phases.size() - 1) {
                        find_output_size(phases[phase]);

                        Node *output_node = phases[phase]->effects.back();

                        if (output_node->output_texture_width != phases[phase]->output_width ||
                            output_node->output_texture_height != phases[phase]->output_height) {
                                glActiveTexture(GL_TEXTURE0);
                                check_error();
                                glBindTexture(GL_TEXTURE_2D, output_node->output_texture);
                                check_error();
                                glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F_ARB, phases[phase]->output_width, phases[phase]->output_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
                                check_error();
                                glBindTexture(GL_TEXTURE_2D, 0);
                                check_error();

                                output_node->output_texture_width = phases[phase]->output_width;
                                output_node->output_texture_height = phases[phase]->output_height;
                        }
                }

                glUseProgram(phases[phase]->glsl_program_num);
                check_error();

                // Set up RTT inputs for this phase.
                for (unsigned sampler = 0; sampler < phases[phase]->inputs.size(); ++sampler) {
                        glActiveTexture(GL_TEXTURE0 + sampler);
                        Node *input = phases[phase]->inputs[sampler];
                        glBindTexture(GL_TEXTURE_2D, input->output_texture);
                        check_error();
                        if (phases[phase]->input_needs_mipmaps) {
                                if (generated_mipmaps.count(input) == 0) {
                                        glGenerateMipmap(GL_TEXTURE_2D);
                                        check_error();
                                        generated_mipmaps.insert(input);
                                }
                                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
                                check_error();
                        } else {
                                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
                                check_error();
                        }

                        std::string texture_name = std::string("tex_") + input->effect_id;
                        glUniform1i(glGetUniformLocation(phases[phase]->glsl_program_num, texture_name.c_str()), sampler);
                        check_error();
                }

                // And now the output.
                if (phase == phases.size() - 1) {
                        // Last phase goes to the output the user specified.
                        glBindFramebuffer(GL_FRAMEBUFFER, dest_fbo);
                        check_error();
                        glViewport(x, y, width, height);
                        if (dither_effect != NULL) {
                                CHECK(dither_effect->set_int("output_width", width));
                                CHECK(dither_effect->set_int("output_height", height));
                        }
                } else {
                        Node *output_node = phases[phase]->effects.back();
                        glFramebufferTexture2D(
                                GL_FRAMEBUFFER,
                                GL_COLOR_ATTACHMENT0,
                                GL_TEXTURE_2D,
                                output_node->output_texture,
                                0);
                        check_error();
                        glViewport(0, 0, phases[phase]->output_width, phases[phase]->output_height);
                }

                // Give the required parameters to all the effects.
                unsigned sampler_num = phases[phase]->inputs.size();
                for (unsigned i = 0; i < phases[phase]->effects.size(); ++i) {
                        Node *node = phases[phase]->effects[i];
                        node->effect->set_gl_state(phases[phase]->glsl_program_num, node->effect_id, &sampler_num);
                        check_error();
                }

                // Now draw!
                glBegin(GL_QUADS);

                glTexCoord2f(0.0f, 0.0f);
                glVertex2f(0.0f, 0.0f);

                glTexCoord2f(1.0f, 0.0f);
                glVertex2f(1.0f, 0.0f);

                glTexCoord2f(1.0f, 1.0f);
                glVertex2f(1.0f, 1.0f);

                glTexCoord2f(0.0f, 1.0f);
                glVertex2f(0.0f, 1.0f);

                glEnd();
                check_error();

                for (unsigned i = 0; i < phases[phase]->effects.size(); ++i) {
                        Node *node = phases[phase]->effects[i];
                        node->effect->clear_gl_state();
                }
        }
}