Add a temporary variable to reduce the amount of tedious typing.

[movit] / effect.h

#ifndef _MOVIT_EFFECT_H
#define _MOVIT_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 <GL/glew.h>
#include <assert.h>
#include <stddef.h>
#include <map>
#include <string>

#include "defs.h"

namespace movit {

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;
};

// Can alias on a float[4].
struct RGBATuple {
        RGBATuple(float r, float g, float b, float a)
                : r(r), g(g), b(b), a(a) {}

        float r, g, b, a;
};

class Effect {
public:
        virtual ~Effect() {}

        // 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; }

        // How this effect handles alpha, ie. what it outputs in its
        // alpha channel. The choices are basically blank (alpha is always 1.0),
        // premultiplied and postmultiplied.
        //
        // Premultiplied alpha is when the alpha value has been be multiplied
        // into the three color components, so e.g. 100% red at 50% alpha
        // would be (0.5, 0.0, 0.0, 0.5) instead of (1.0, 0.0, 0.0, 0.5)
        // as it is stored in most image formats (postmultiplied alpha).
        // The multiplication is taken to have happened in linear light.
        // This is the most natural format for processing, and the default in
        // most of Movit (just like linear light is).
        //
        // If you set INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA or
        // INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK, all of your inputs
        // (if any) are guaranteed to also be in premultiplied alpha.
        // Otherwise, you can get postmultiplied or premultiplied alpha;
        // you won't know. If you have multiple inputs, you will get the same
        // (pre- or postmultiplied) for all inputs, although most likely,
        // you will want to combine them in a premultiplied fashion anyway
        // in that case.
        enum AlphaHandling {
                // Always outputs blank alpha (ie. alpha=1.0). Only appropriate
                // for inputs that do not output an alpha channel.
                // Blank alpha is special in that it can be treated as both
                // pre- and postmultiplied.
                OUTPUT_BLANK_ALPHA,

                // Always outputs postmultiplied alpha. Only appropriate for inputs.
                OUTPUT_POSTMULTIPLIED_ALPHA,

                // Always outputs premultiplied alpha. As noted above,
                // you will then also get all inputs in premultiplied alpha.
                // If you set this, you should also set needs_linear_light().
                INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA,

                // Like INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA, but also guarantees
                // that if you get blank alpha in, you also keep blank alpha out.
                // This is a somewhat weaker guarantee than DONT_CARE_ALPHA_TYPE,
                // but is still useful in many situations, and appropriate when
                // e.g. you don't touch alpha at all.
                //
                // Does not make sense for inputs.
                INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK,

                // Keeps the type of alpha (premultiplied, postmultiplied, blank)
                // unchanged from input to output. Usually appropriate if you
                // process all color channels in a linear fashion, do not change
                // alpha, and do not produce any new pixels thare have alpha != 1.0.
                //
                // Does not make sense for inputs.
                DONT_CARE_ALPHA_TYPE,
        };
        virtual AlphaHandling alpha_handling() const { return INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA; }

        // 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 1:1 between pixels and texels, 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) (see inform_input_size(), below). 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; }

        // Whether this effect is effectively sampling from a a single texture.
        // If so, it will override needs_texture_bounce(); however, there are also
        // two demands it needs to fulfill:
        //
        //  1. It needs to be an Input, ie. num_inputs() == 0.
        //  2. It needs to allocate exactly one sampler in set_gl_state(),
        //     and allow dependent effects to change that sampler state.
        virtual bool is_single_texture() const { return false; }

        // If changes_output_size() is true, you must implement this to tell
        // the framework what output size you want. Also, you can set a
        // virtual width/height, which is the size the next effect (if any)
        // will _think_ your data is in. This is primarily useful if you are
        // relying on getting OpenGL's bilinear resizing for free; otherwise,
        // your virtual_width/virtual_height should be the same as width/height.
        //
        // 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,
                                     unsigned *virtual_width, unsigned *virtual_height) const {
                assert(false);
        }

        // Tells the effect the resolution of each of its input.
        // This will be called every frame, and always before get_output_size(),
        // so you can change your output size based on the input if so desired.
        //
        // Note that in some cases, an input might not have a single well-defined
        // resolution (for instance if you fade between two inputs with
        // different resolutions). In this case, you will get width=0 and height=0
        // for that input. If you cannot handle that, you will need to set
        // needs_texture_bounce() to true, which will force a render to a single
        // given resolution before you get the input.
        virtual void inform_input_size(unsigned input_num, unsigned width, unsigned height) {}

        // 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; }

        // Inform the effect that it has been just added to the EffectChain.
        // The primary use for this is to store the ResourcePool uesd by
        // the chain; for modifications to it, rewrite_graph() below
        // is probably a better fit.
        virtual void inform_added(EffectChain *chain) {}

        // 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) MUST_CHECK_RESULT;
        virtual bool set_float(const std::string &key, float value) MUST_CHECK_RESULT;
        virtual bool set_vec2(const std::string &key, const float *values) MUST_CHECK_RESULT;
        virtual bool set_vec3(const std::string &key, const float *values) MUST_CHECK_RESULT;
        virtual bool set_vec4(const std::string &key, const float *values) MUST_CHECK_RESULT;

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/vec4 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);
        void register_vec4(const std::string &key, float *values);

private:
        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, float *> params_vec4;
};

}  // namespace movit

#endif // !defined(_MOVIT_EFFECT_H)