From aa987216b92584aafc0ecbc3d578606018078f91 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 28 Dec 2013 17:14:07 +0200
Subject: [PATCH] Add gamma correction and sRGB conversion support to
 ColorCurve

---
 source/colorcurve.cpp | 47 ++++++++++++++++++++++++++++++++++++++-----
 source/colorcurve.h   |  6 ++++++
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/source/colorcurve.cpp b/source/colorcurve.cpp
index ae09b7e6..6351ea20 100644
--- a/source/colorcurve.cpp
+++ b/source/colorcurve.cpp
@@ -1,3 +1,4 @@
+#include <cmath>
 #include "colorcurve.h"
 #include "mesh.h"
 #include "shader.h"
@@ -9,6 +10,7 @@ namespace {
 
 static const char fragment_src[] =
 	"uniform sampler2D texture;\n"
+	"uniform sampler1D curve;\n"
 	"uniform float peak;\n"
 	"uniform float brightness;\n"
 	"varying vec2 texcoord;\n"
@@ -21,17 +23,15 @@ static const char fragment_src[] =
 	"		vec3 saturated = sample.rgb/maxc;\n"
 	"		if(maxc>1.0+peak)\n"
 	"		{\n"
-	"			gl_FragColor.rgb = mix(vec3(1.0), saturated, 1.0/pow(brightness, maxc-1.0-peak));\n"
+	"			sample.rgb = mix(vec3(1.0), saturated, 1.0/pow(brightness, maxc-1.0-peak));\n"
 	"		}\n"
 	"		else\n"
 	"		{\n"
 	"			float x = (1.0+peak-maxc)/(2.0*peak);\n"
-	"			gl_FragColor.rgb = saturated.rgb*(1.0-peak+(1.0-x*x)*peak);\n"
+	"			sample.rgb = saturated.rgb*(1.0-peak+(1.0-x*x)*peak);\n"
 	"		}\n"
-	"		gl_FragColor.a = sample.a;\n"
 	"	}\n"
-	"	else\n"
-	"		gl_FragColor = sample;\n"
+	"	gl_FragColor = vec4(texture1D(curve, sample.r).r, texture1D(curve, sample.g).r, texture1D(curve, sample.b).r, sample.a);\n"
 	"}";
 
 }
@@ -46,8 +46,16 @@ ColorCurve::ColorCurve():
 	shprog.attach_shader_owned(new FragmentShader(fragment_src));
 	shprog.link();
 
+	shdata.uniform("texture", 0);
+	shdata.uniform("curve", 1);
+
+	curve.storage(LUMINANCE, 256);
+	curve.set_min_filter(LINEAR);
+	curve.set_wrap(CLAMP_TO_EDGE);
+
 	set_peak(0.2);
 	set_brightness(1.5);
+	set_linear();
 }
 
 void ColorCurve::set_peak(float p)
@@ -64,11 +72,40 @@ void ColorCurve::set_brightness(float b)
 	shdata.uniform("brightness", b);
 }
 
+void ColorCurve::set_gamma(float g)
+{
+	if(g<0.1 || g>10)
+		throw invalid_argument("ColorCurve::set_gamma");
+
+	unsigned char curve_data[256];
+	for(unsigned i=0; i<256; ++i)
+		curve_data[i] = pow(i/255.0f, 1/g)*255+0.5f;
+	curve.image(0, LUMINANCE, UNSIGNED_BYTE, curve_data);
+}
+
+void ColorCurve::set_srgb()
+{
+	unsigned char curve_data[256];
+	curve_data[0] = 0;
+	for(unsigned i=1; i<256; ++i)
+		curve_data[i] = (1.055*pow(i/255.0f, 1/2.4f)-0.055)*255+0.5;
+	curve.image(0, LUMINANCE, UNSIGNED_BYTE, curve_data);
+}
+
+void ColorCurve::set_linear()
+{
+	unsigned char curve_data[256];
+	for(unsigned i=0; i<256; ++i)
+		curve_data[i] = i;
+	curve.image(0, LUMINANCE, UNSIGNED_BYTE, curve_data);
+}
+
 void ColorCurve::render(const Texture2D &color_buf, const Texture2D &)
 {
 	Bind _bind_shader(shprog);
 	shdata.apply();
 	Bind _bind_tex(color_buf);
+	Bind _bind_curve(curve, 1);
 	quad.draw();
 }
 
diff --git a/source/colorcurve.h b/source/colorcurve.h
index 74a19d04..75e7fd30 100644
--- a/source/colorcurve.h
+++ b/source/colorcurve.h
@@ -4,6 +4,7 @@
 #include "postprocessor.h"
 #include "program.h"
 #include "programdata.h"
+#include "texture1d.h"
 
 namespace Msp {
 namespace GL {
@@ -20,6 +21,7 @@ class ColorCurve: public PostProcessor
 private:
 	Program shprog;
 	ProgramData shdata;
+	Texture1D curve;
 	const Mesh &quad;
 
 public:
@@ -33,6 +35,10 @@ public:
 	saturated value. */
 	void set_brightness(float);
 
+	void set_gamma(float);
+	void set_srgb();
+	void set_linear();
+
 	virtual void render(const Texture2D &, const Texture2D &);
 };
 
-- 
2.45.2