Add a file-level comment for EffectChain.

[movit] / effect_chain.h

#ifndef _MOVIT_EFFECT_CHAIN_H
#define _MOVIT_EFFECT_CHAIN_H 1

// An EffectChain is the largest basic entity in Movit; it contains everything
// needed to connects a series of effects, from inputs to outputs, and render
// them. Generally you set up your effect chain once and then call its render
// functions once per frame; setting one up can be relatively expensive,
// but rendering is fast.

#include <GL/glew.h>
#include <stdio.h>
#include <map>
#include <set>
#include <string>
#include <vector>

#include "image_format.h"

class Effect;
class Input;
struct Phase;

// For internal use within Node.
enum AlphaType {
        ALPHA_INVALID = -1,
        ALPHA_BLANK,
        ALPHA_PREMULTIPLIED,
        ALPHA_POSTMULTIPLIED,
};

// Whether you want pre- or postmultiplied alpha in the output
// (see effect.h for a discussion of pre- versus postmultiplied alpha).
enum OutputAlphaFormat {
        OUTPUT_ALPHA_FORMAT_PREMULTIPLIED,
        OUTPUT_ALPHA_FORMAT_POSTMULTIPLIED,
};

// A node in the graph; basically an effect and some associated information.
class Node {
public:
        Effect *effect;
        bool disabled;

        // Edges in the graph (forward and backward).
        std::vector<Node *> outgoing_links;
        std::vector<Node *> incoming_links;

private:
        // Identifier used to create unique variables in GLSL.
        std::string effect_id;

        // Logical size of the output of this effect, ie. the resolution
        // you would get if you sampled it as a texture. If it is undefined
        // (since the inputs differ in resolution), it will be 0x0.
        // If both this and output_texture_{width,height} are set,
        // they will be equal.
        unsigned output_width, output_height;

        // If output goes to RTT (otherwise, none of these are set).
        // The Phase pointer is a but ugly; we should probably fix so
        // that Phase takes other phases as inputs, instead of Node.
        GLuint output_texture;
        unsigned output_texture_width, output_texture_height;
        Phase *phase;

        // Used during the building of the effect chain.
        Colorspace output_color_space;
        GammaCurve output_gamma_curve;
        AlphaType output_alpha_type;

        friend class EffectChain;
};

// A rendering phase; a single GLSL program rendering a single quad.
struct Phase {
        GLint glsl_program_num, vertex_shader, fragment_shader;
        bool input_needs_mipmaps;

        // Inputs are only inputs from other phases (ie., those that come from RTT);
        // input textures are not counted here.
        std::vector<Node *> inputs;

        std::vector<Node *> effects;  // In order.
        unsigned output_width, output_height, virtual_output_width, virtual_output_height;
};

class EffectChain {
public:
        EffectChain(float aspect_nom, float aspect_denom);  // E.g., 16.0f, 9.0f for 16:9.
        ~EffectChain();

        // User API:
        // input, effects, output, finalize need to come in that specific order.

        // EffectChain takes ownership of the given input.
        // input is returned back for convenience.
        Input *add_input(Input *input);

        // EffectChain takes ownership of the given effect.
        // effect is returned back for convenience.
        Effect *add_effect(Effect *effect) {
                return add_effect(effect, last_added_effect());
        }
        Effect *add_effect(Effect *effect, Effect *input) {
                std::vector<Effect *> inputs;
                inputs.push_back(input);
                return add_effect(effect, inputs);
        }
        Effect *add_effect(Effect *effect, Effect *input1, Effect *input2) {
                std::vector<Effect *> inputs;
                inputs.push_back(input1);
                inputs.push_back(input2);
                return add_effect(effect, inputs);
        }
        Effect *add_effect(Effect *effect, const std::vector<Effect *> &inputs);

        void add_output(const ImageFormat &format, OutputAlphaFormat alpha_format);

        // Set number of output bits, to scale the dither.
        // 8 is the right value for most outputs.
        // The default, 0, is a special value that means no dither.
        void set_dither_bits(unsigned num_bits)
        {
                this->num_dither_bits = num_bits;
        }

        void finalize();


        //void render(unsigned char *src, unsigned char *dst);
        void render_to_screen()
        {
                render_to_fbo(0, 0, 0);
        }

        // Render the effect chain to the given FBO. If width=height=0, keeps
        // the current viewport.
        void render_to_fbo(GLuint fbo, unsigned width, unsigned height);

        Effect *last_added_effect() {
                if (nodes.empty()) {
                        return NULL;
                } else {
                        return nodes.back()->effect;
                }       
        }

        // API for manipulating the graph directly. Intended to be used from
        // effects and by EffectChain itself.
        //
        // Note that for nodes with multiple inputs, the order of calls to
        // connect_nodes() will matter.
        Node *add_node(Effect *effect);
        void connect_nodes(Node *sender, Node *receiver);
        void replace_receiver(Node *old_receiver, Node *new_receiver);
        void replace_sender(Node *new_sender, Node *receiver);
        void insert_node_between(Node *sender, Node *middle, Node *receiver);

private:
        // Make sure the output rectangle is at least large enough to hold
        // the given input rectangle in both dimensions, and is of the
        // current aspect ratio (aspect_nom/aspect_denom).
        void size_rectangle_to_fit(unsigned width, unsigned height, unsigned *output_width, unsigned *output_height);

        // Compute the input sizes for all inputs for all effects in a given phase,
        // and inform the effects about the results.    
        void inform_input_sizes(Phase *phase);

        // Determine the preferred output size of a given phase.
        // Requires that all input phases (if any) already have output sizes set.
        void find_output_size(Phase *phase);

        // Find all inputs eventually feeding into this effect that have
        // output gamma different from GAMMA_LINEAR.
        void find_all_nonlinear_inputs(Node *effect, std::vector<Node *> *nonlinear_inputs);

        // Create a GLSL program computing the given effects in order.
        Phase *compile_glsl_program(const std::vector<Node *> &inputs,
                                    const std::vector<Node *> &effects);

        // Create all GLSL programs needed to compute the given effect, and all outputs
        // that depends on it (whenever possible).
        void construct_glsl_programs(Node *output);

        // Output the current graph to the given file in a Graphviz-compatible format;
        // only useful for debugging.
        void output_dot(const char *filename);
        std::vector<std::string> get_labels_for_edge(const Node *from, const Node *to);
        void output_dot_edge(FILE *fp,
                             const std::string &from_node_id,
                             const std::string &to_node_id,
                             const std::vector<std::string> &labels);

        // Some of the graph algorithms assume that the nodes array is sorted
        // topologically (inputs are always before outputs), but some operations
        // (like graph rewriting) can change that. This function restores that order.
        void sort_all_nodes_topologically();

        // Do the actual topological sort. <nodes> must be a connected, acyclic subgraph;
        // links that go to nodes not in the set will be ignored.
        std::vector<Node *> topological_sort(const std::vector<Node *> &nodes);

        // Utility function used by topological_sort() to do a depth-first search.
        // The reason why we store nodes left to visit instead of a more conventional
        // list of nodes to visit is that we want to be able to limit ourselves to
        // a subgraph instead of all nodes. The set thus serves a dual purpose.
        void topological_sort_visit_node(Node *node, std::set<Node *> *nodes_left_to_visit, std::vector<Node *> *sorted_list);

        // Used during finalize().
        void find_color_spaces_for_inputs();
        void propagate_alpha();
        void propagate_gamma_and_color_space();
        Node *find_output_node();

        bool node_needs_colorspace_fix(Node *node);
        void fix_internal_color_spaces();
        void fix_output_color_space();

        bool node_needs_alpha_fix(Node *node);
        void fix_internal_alpha(unsigned step);
        void fix_output_alpha();

        bool node_needs_gamma_fix(Node *node);
        void fix_internal_gamma_by_asking_inputs(unsigned step);
        void fix_internal_gamma_by_inserting_nodes(unsigned step);
        void fix_output_gamma();
        void add_dither_if_needed();

        float aspect_nom, aspect_denom;
        ImageFormat output_format;
        OutputAlphaFormat output_alpha_format;

        std::vector<Node *> nodes;
        std::map<Effect *, Node *> node_map;
        Effect *dither_effect;

        std::vector<Input *> inputs;  // Also contained in nodes.
        std::vector<Phase *> phases;

        unsigned num_dither_bits;
        bool finalized;
};

#endif // !defined(_MOVIT_EFFECT_CHAIN_H)