X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=lift_gamma_gain_effect.h;h=6e2ea19a4d54231620d6eb6039e67571a98e5c16;hp=0c42319166046bb05c1bcb6d468e29bd5c7cbf64;hb=eff011224abc5dc81f801f3ea44572287a55bcac;hpb=96a1cff51a8b7dc45ebe725e0d0685eecce31331

diff --git a/lift_gamma_gain_effect.h b/lift_gamma_gain_effect.h
index 0c42319..6e2ea19 100644
--- a/lift_gamma_gain_effect.h
+++ b/lift_gamma_gain_effect.h
@@ -1,17 +1,47 @@
-#ifndef _LIFT_GAMMA_GAIN_EFFECT_H
-#define _LIFT_GAMMA_GAIN_EFFECT_H 1
+#ifndef _MOVIT_LIFT_GAMMA_GAIN_EFFECT_H
+#define _MOVIT_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 <epoxy/gl.h>
+#include <string>
 
 #include "effect.h"
 
+namespace movit {
+
 class LiftGammaGainEffect : public Effect {
 public:
 	LiftGammaGainEffect();
-	std::string output_glsl();
+	std::string effect_type_id() const override { return "LiftGammaGainEffect"; }
+	AlphaHandling alpha_handling() const override { return INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK; }
+	bool strong_one_to_one_sampling() const override { return true; }
+	std::string output_fragment_shader() override;
 
-	void set_uniforms(GLuint glsl_program_num, const std::string &prefix);
+	void set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num) override;
 
 private:
 	RGBTriplet lift, gamma, gain;
+	RGBTriplet uniform_gain_pow_inv_gamma, uniform_inv_gamma22;
 };
 
-#endif // !defined(_LIFT_GAMMA_GAIN_EFFECT_H)
+}  // namespace movit
+
+#endif // !defined(_MOVIT_LIFT_GAMMA_GAIN_EFFECT_H)