X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=lift_gamma_gain_effect.h;h=bd1ec16a6d8743e6dfa83cd9848e78b959636a7c;hp=26eb583f3489f0c1101db3dec461bc37a4cfe9a4;hb=ac040289928cdf3554ce884575afab17565e6c67;hpb=a592c55caca0fb654bad4ec43b84c46abcee21c2

diff --git a/lift_gamma_gain_effect.h b/lift_gamma_gain_effect.h
index 26eb583..bd1ec16 100644
--- a/lift_gamma_gain_effect.h
+++ b/lift_gamma_gain_effect.h
@@ -1,16 +1,41 @@
 #ifndef _LIFT_GAMMA_GAIN_EFFECT_H
 #define _LIFT_GAMMA_GAIN_EFFECT_H 1
 
+// A simple lift/gamma/gain effect, used for color grading.
+//
+// Very roughly speaking, lift=shadows, gamma=midtones and gain=highlights,
+// although all parameters affect the entire curve. Mathematically speaking,
+// it is a bit unusual to look at gamma as a color, but it works pretty well
+// in practice.
+//
+// The classic formula is: output = (gain * (x + lift * (1-x)))^(1/gamma).
+//
+// The lift is actually a case where we actually would _not_ want linear light;
+// since black by definition becomes equal to the lift color, we want lift to
+// be pretty close to black, but in linear light that means lift affects the
+// rest of the curve relatively little. Thus, we actually convert to gamma 2.2
+// before lift, and then back again afterwards. (Gain and gamma are,
+// up to constants, commutative with the de-gamma operation.)
+//
+// Also, gamma is a case where we would not want premultiplied alpha.
+// Thus, we have to divide away alpha first, and then re-multiply it back later.
+
+#include <GL/glew.h>
+#include <string>
+
 #include "effect.h"
 
 class LiftGammaGainEffect : public Effect {
 public:
 	LiftGammaGainEffect();
-	std::string output_glsl();
+	virtual std::string effect_type_id() const { return "LiftGammaGainEffect"; }
+	virtual AlphaHandling alpha_handling() const { return INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK; }
+	std::string output_fragment_shader();
+
+	void set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num);
 
 private:
 	RGBTriplet lift, gamma, gain;
-	float saturation;
 };
 
 #endif // !defined(_LIFT_GAMMA_GAIN_EFFECT_H)