#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 <epoxy/gl.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)