From 9a54442d865974ac8785988e7e740480e72ab24c Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 20 Aug 2012 23:30:51 +0300
Subject: [PATCH] Add a color curve post-processor

---
 source/colorcurve.cpp | 77 +++++++++++++++++++++++++++++++++++++++++++
 source/colorcurve.h   | 42 +++++++++++++++++++++++
 2 files changed, 119 insertions(+)
 create mode 100644 source/colorcurve.cpp
 create mode 100644 source/colorcurve.h

diff --git a/source/colorcurve.cpp b/source/colorcurve.cpp
new file mode 100644
index 00000000..95c82491
--- /dev/null
+++ b/source/colorcurve.cpp
@@ -0,0 +1,77 @@
+#include "colorcurve.h"
+#include "mesh.h"
+#include "shader.h"
+#include "texture2d.h"
+
+using namespace std;
+
+namespace {
+
+static const char fragment_src[] =
+	"uniform sampler2D texture;\n"
+	"uniform float peak;\n"
+	"uniform float brightness;\n"
+	"varying vec2 texcoord;\n"
+	"void main()\n"
+	"{\n"
+	"	vec4 sample = texture2D(texture, texcoord);\n"
+	"	float maxc = max(sample.r, max(sample.g, sample.b));\n"
+	"	if(maxc>1.0-peak)\n"
+	"	{\n"
+	"		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-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-x*x)*peak);\n"
+	"		}\n"
+	"		gl_FragColor.a = sample.a;\n"
+	"	}\n"
+	"	else\n"
+	"		gl_FragColor = sample;\n"
+	"}";
+
+}
+
+namespace Msp {
+namespace GL {
+
+ColorCurve::ColorCurve():
+	quad(get_fullscreen_quad())
+{
+	shprog.attach_shader(get_fullscreen_vertex_shader());
+	Shader *fs = new Shader(FRAGMENT_SHADER, fragment_src);
+	shprog.attach_shader_owned(fs);
+	shprog.link();
+
+	set_peak(0.2);
+	set_brightness(1.5);
+}
+
+void ColorCurve::set_peak(float p)
+{
+	if(p<0 || p>1)
+		throw invalid_argument("ColorCurve::set_peak");
+	shdata.uniform("peak", p);
+}
+
+void ColorCurve::set_brightness(float b)
+{
+	if(b<1)
+		throw invalid_argument("ColorCurve::set_brightness");
+	shdata.uniform("brightness", b);
+}
+
+void ColorCurve::render(const Texture2D &color_buf, const Texture2D &)
+{
+	Bind _bind_shader(shprog);
+	shdata.apply();
+	Bind _bind_tex(color_buf);
+	quad.draw();
+}
+
+} // namespace GL
+} // namespace Msp
diff --git a/source/colorcurve.h b/source/colorcurve.h
new file mode 100644
index 00000000..82a8526f
--- /dev/null
+++ b/source/colorcurve.h
@@ -0,0 +1,42 @@
+#ifndef COLORCURVE_H_
+#define COLORCURVE_H_
+
+#include "postprocessor.h"
+#include "program.h"
+#include "programdata.h"
+
+namespace Msp {
+namespace GL {
+
+/**
+Processes oversaturated colors to preserve hues.  When one color component 
+exceeds 1.0, the others are scaled towards white.  A transition curve is also
+applied near 1.0 to prevent the abrupt change in the gradient.
+
+Only makes sense when used in an HDR framebuffer.
+*/
+class ColorCurve: public PostProcessor
+{
+private:
+	Program shprog;
+	ProgramData shdata;
+	const Mesh &quad;
+
+public:
+	ColorCurve();
+
+	/// Sets the size of the peak zone.  Must be between 0 and 1, inclusive.
+	void set_peak(float);
+
+	/** Sets brightness for oversaturated colors.  Must be >= 1.  Suggested
+	values are between 1.5 and 2.0; a value of 1.0 will clamp colors to the
+	saturated value. */
+	void set_brightness(float);
+
+	virtual void render(const Texture2D &, const Texture2D &);
+};
+
+} // namespace GL
+} // namespace Msp
+
+#endif
-- 
2.45.2