-#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();
+ 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_uniforms(GLhandleARB glsl_program_num, const std::string &prefix);
+ 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)
+} // namespace movit
+
+#endif // !defined(_MOVIT_LIFT_GAMMA_GAIN_EFFECT_H)