[movit] / effect.h

#ifndef _EFFECT_H
#define _EFFECT_H 1

// Effect is the base class for every effect. It basically represents a single
// GLSL function, with an optional set of user-settable parameters.
//
// A note on naming: Since all effects run in the same GLSL namespace,
// you can't use any name you want for global variables (e.g. uniforms).
// The framework assigns a prefix to you which will be unique for each
// effect instance; use the macro PREFIX() around your identifiers to
// automatically prepend that prefix.

#include <map>
#include <string>
#include <vector>

#include <assert.h>

#include "opengl.h"

class EffectChain;
class Node;

// Can alias on a float[2].
struct Point2D {
        Point2D(float x, float y)
                : x(x), y(y) {}

        float x, y;
};

// Can alias on a float[3].
struct RGBTriplet {
        RGBTriplet(float r, float g, float b)
                : r(r), g(g), b(b) {}

        float r, g, b;
};

// Convenience functions that deal with prepending the prefix.
GLint get_uniform_location(GLuint glsl_program_num, const std::string &prefix, const std::string &key);
void set_uniform_int(GLuint glsl_program_num, const std::string &prefix, const std::string &key, int value);
void set_uniform_float(GLuint glsl_program_num, const std::string &prefix, const std::string &key, float value);
void set_uniform_float_array(GLuint glsl_program_num, const std::string &prefix, const std::string &key, const float *values, size_t num_values);
void set_uniform_vec2(GLuint glsl_program_num, const std::string &prefix, const std::string &key, const float *values);
void set_uniform_vec3(GLuint glsl_program_num, const std::string &prefix, const std::string &key, const float *values);
void set_uniform_vec4_array(GLuint glsl_program_num, const std::string &prefix, const std::string &key, const float *values, size_t num_values);

class Effect {
public:
        // An identifier for this type of effect, mostly used for debug output
        // (but some special names, like "ColorSpaceConversionEffect", holds special
        // meaning). Same as the class name is fine.
        virtual std::string effect_type_id() const = 0;

        // Whether this effects expects its input (and output) to be in
        // linear gamma, ie. without an applied gamma curve. Most effects
        // will want this, although the ones that never actually look at
        // the pixels, e.g. mirror, won't need to care, and can set this
        // to false. If so, the input gamma will be undefined.
        //
        // Also see the note on needs_texture_bounce(), below.
        virtual bool needs_linear_light() const { return true; }

        // Whether this effect expects its input to be in the sRGB
        // color space, ie. use the sRGB/Rec. 709 RGB primaries.
        // (If not, it would typically come in as some slightly different
        // set of RGB primaries; you would currently not get YCbCr
        // or something similar).
        //
        // Again, most effects will want this, but you can set it to false
        // if you process each channel independently, equally _and_
        // in a linear fashion.
        virtual bool needs_srgb_primaries() const { return true; }

        // Whether this effect expects its input to come directly from
        // a texture. If this is true, the framework will not chain the
        // input from other effects, but will store the results of the
        // chain to a temporary (RGBA fp16) texture and let this effect
        // sample directly from that.
        //
        // There are two good reasons why you might want to set this:
        //
        //  1. You are sampling more than once from the input,
        //     in which case computing all the previous steps might
        //     be more expensive than going to a memory intermediate.
        //  2. You rely on previous effects, possibly including gamma
        //     expansion, to happen pre-filtering instead of post-filtering.
        //     (This is only relevant if you actually need the filtering; if
        //     you sample on whole input pixels only, it makes no difference.)
        //
        // Note that in some cases, you might get post-filtered gamma expansion
        // even when setting this option. More specifically, if you are the
        // first effect in the chain, and the GPU is doing sRGB gamma
        // expansion, it is undefined (from OpenGL's side) whether expansion
        // happens pre- or post-filtering. For most uses, however,
        // either will be fine.
        virtual bool needs_texture_bounce() const { return false; }

        // Whether this effect expects mipmaps or not. If you set this to
        // true, you will be sampling with bilinear filtering; if not,
        // you could be sampling with simple linear filtering and no mipmaps
        // (although there is no guarantee; if a different effect in the chain
        // needs mipmaps, you will also get them).
        virtual bool needs_mipmaps() const { return false; }

        // Whether this effect wants to output to a different size than
        // its input(s). If you set this to true, the output will be
        // bounced to a texture (similarly to if the next effect set
        // needs_texture_bounce()).
        virtual bool changes_output_size() const { return false; }

        // If changes_output_size() is true, you must implement this to tell
        // the framework what output size you want.
        //
        // Note that it is explicitly allowed to change width and height
        // from frame to frame; EffectChain will reallocate textures as needed.
        virtual void get_output_size(unsigned *width, unsigned *height) const {
                assert(false);
        }

        // How many inputs this effect will take (a fixed number).
        // If you have only one input, it will be called INPUT() in GLSL;
        // if you have several, they will be INPUT1(), INPUT2(), and so on.
        virtual unsigned num_inputs() const { return 1; }

        // Let the effect rewrite the effect chain as it sees fit.
        // Most effects won't need to do this, but this is very useful
        // if you have an effect that consists of multiple sub-effects
        // (for instance, two passes). The effect is given to its own
        // pointer, and it can add new ones (by using add_node()
        // and connect_node()) as it sees fit. This is called at
        // EffectChain::finalize() time, when the entire graph is known,
        // in the order that the effects were originally added.
        //
        // Note that if the effect wants to take itself entirely out
        // of the chain, it must set “disabled” to true and then disconnect
        // itself from all other effects.
        virtual void rewrite_graph(EffectChain *graph, Node *self) {}

        // Outputs one GLSL uniform declaration for each registered parameter
        // (see below), with the right prefix prepended to each uniform name.
        // If you do not want this behavior, you can override this function.
        virtual std::string output_convenience_uniforms() const;

        // Returns the GLSL fragment shader string for this effect.
        virtual std::string output_fragment_shader() = 0;

        // Set all OpenGL state that this effect needs before rendering.
        // The default implementation sets one uniform per registered parameter,
        // but no other state.
        //
        // <sampler_num> is the first free texture sampler. If you want to use
        // textures, you can bind a texture to GL_TEXTURE0 + <sampler_num>,
        // and then increment the number (so that the next effect in the chain
        // will use a different sampler).
        virtual void set_gl_state(GLuint glsl_program_num, const std::string& prefix, unsigned *sampler_num);

        // If you set any special OpenGL state in set_gl_state(), you can clear it
        // after rendering here. The default implementation does nothing.
        virtual void clear_gl_state();

        // Set a parameter; intended to be called from user code.
        // Neither of these take ownership of the pointer.
        virtual bool set_int(const std::string&, int value);
        virtual bool set_float(const std::string &key, float value);
        virtual bool set_vec2(const std::string &key, const float *values);
        virtual bool set_vec3(const std::string &key, const float *values);

protected:
        // Register a parameter. Whenever set_*() is called with the same key,
        // it will update the value in the given pointer (typically a pointer
        // to some private member variable in your effect).
        //
        // Neither of these take ownership of the pointer.

        // int is special since GLSL pre-1.30 doesn't have integer uniforms.
        // Thus, ints that you register will _not_ be converted to GLSL uniforms.
        void register_int(const std::string &key, int *value);

        // These correspond directly to float/vec2/vec3 in GLSL.
        void register_float(const std::string &key, float *value);
        void register_vec2(const std::string &key, float *values);
        void register_vec3(const std::string &key, float *values);

        // This will register a 1D texture, which will be bound to a sampler
        // when your GLSL code runs (so it corresponds 1:1 to a sampler2D uniform
        // in GLSL).
        //
        // Note that if you change the contents of <values>, you will need to
        // call invalidate_1d_texture() to have the picture re-uploaded on the
        // next frame. This is in contrast to all the other parameters, which are
        // set anew every frame.
        void register_1d_texture(const std::string &key, float *values, size_t size);
        void invalidate_1d_texture(const std::string &key);
        
private:
        struct Texture1D {
                float *values;
                size_t size;
                bool needs_update;
                GLuint texture_num;
        };

        std::map<std::string, int *> params_int;
        std::map<std::string, float *> params_float;
        std::map<std::string, float *> params_vec2;
        std::map<std::string, float *> params_vec3;
        std::map<std::string, Texture1D> params_tex_1d;
};

#endif // !defined(_EFFECT_H)