HSV shift

shader/hue.frag

@@ -1,12 +1,36 @@
 
 uniform sampler2D texture;
-uniform lowp mat3 rotationMat;
+uniform mediump float hueAdjust;
 
 varying vec2 v_texCoord;
 
+/* Source: gamedev.stackexchange.com/a/59808/24839 */
+vec3 rgb2hsv(vec3 c)
+{
+	const vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
+	vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
+	vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));
+
+	float d = q.x - min(q.w, q.y);
+	/* Avoid divide-by-zero situations by adding a very tiny delta */
+	const float eps = 1.0e-10;
+	return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + eps)), d / (q.x + eps), q.x);
+}
+
+vec3 hsv2rgb(vec3 c)
+{
+	const vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
+	vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
+	return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
+}
+
 void main ()
 {
 	vec4 color = texture2D (texture, v_texCoord.xy);
+	vec3 hsv = rgb2hsv(color.rgb);
 
-	gl_FragColor = vec4(rotationMat * color.rgb, color.a);
+	hsv.x += hueAdjust;
+	color.rgb = hsv2rgb(hsv);
+
+	gl_FragColor = color;
 }

src/bitmap.cpp

@@ -29,8 +29,6 @@
 
 #include <pixman.h>
 
-#include <math.h>
-
 #include "gl-util.h"
 #include "gl-meta.h"
 #include "quad.h"
@@ -856,28 +854,10 @@ void Bitmap::hueChange(int hue)
 	quad.setTexPosRect(texRect, texRect);
 	quad.setColor(Vec4(1, 1, 1, 1));
 
-	/* Calculate hue rotation matrix */
-	hue = wrapRange(hue, 0, 359);
-	float hueRad = (M_PI / 180.0f) * hue;
-	float x = cos(hueRad);
-	float y = sin(hueRad);
-	float a = (1.0f - x) / 3.0f;
-	float b = sqrt(1.0f / 3.0f) * y;
-
-	float mat[9];
-	mat[0] = x + a;
-	mat[1] = a + b;
-	mat[2] = a - b;
-	mat[3] = mat[2];
-	mat[4] = mat[0];
-	mat[5] = mat[1];
-	mat[6] = mat[1];
-	mat[7] = mat[2];
-	mat[8] = mat[0];
-
 	HueShader &shader = shState->shaders().hue;
 	shader.bind();
-	shader.setRotationMat(mat);
+	/* Shader expects normalized value */
+	shader.setHueAdjust(wrapRange(hue, 0, 359) / 360.0f);
 
 	FBO::bind(newTex.fbo);
 	p->pushSetViewport(shader);

src/gl-fun.h

@@ -90,7 +90,6 @@ typedef void (APIENTRYP _PFNGLUNIFORM1FPROC) (GLint location, GLfloat v0);
 typedef void (APIENTRYP _PFNGLUNIFORM2FPROC) (GLint location, GLfloat v0, GLfloat v1);
 typedef void (APIENTRYP _PFNGLUNIFORM4FPROC) (GLint location, GLfloat v0, GLfloat v1, GLfloat v2, GLfloat v3);
 typedef void (APIENTRYP _PFNGLUNIFORM1IPROC) (GLint location, GLint v0);
-typedef void (APIENTRYP _PFNGLUNIFORMMATRIX3FVPROC) (GLint location, GLsizei count, GLboolean transpose, const GLfloat* value);
 typedef void (APIENTRYP _PFNGLUNIFORMMATRIX4FVPROC) (GLint location, GLsizei count, GLboolean transpose, const GLfloat* value);
 
 /* Vertex attribute */
@@ -175,7 +174,6 @@ typedef void (APIENTRYP _PFNGLRELEASESHADERCOMPILERPROC) (void);
 	GL_FUN(Uniform2f, _PFNGLUNIFORM2FPROC) \
 	GL_FUN(Uniform4f, _PFNGLUNIFORM4FPROC) \
 	GL_FUN(Uniform1i, _PFNGLUNIFORM1IPROC) \
-	GL_FUN(UniformMatrix3fv, _PFNGLUNIFORMMATRIX3FVPROC) \
 	GL_FUN(UniformMatrix4fv, _PFNGLUNIFORMMATRIX4FVPROC) \
 	/* Vertex attribute */ \
 	GL_FUN(BindAttribLocation, _PFNGLBINDATTRIBLOCATIONPROC) \

src/shader.cpp

@@ -550,12 +550,12 @@ HueShader::HueShader()
 
 	ShaderBase::init();
 
-	GET_U(rotationMat);
+	GET_U(hueAdjust);
 }
 
-void HueShader::setRotationMat(const float value[9])
+void HueShader::setHueAdjust(float value)
 {
-	gl.UniformMatrix3fv(u_rotationMat, 1, GL_FALSE, value);
+	gl.Uniform1f(u_hueAdjust, value);
 }
 
 

src/shader.h

@@ -240,10 +240,10 @@ class HueShader : public ShaderBase
 public:
 	HueShader();
 
-	void setRotationMat(const float value[9]);
+	void setHueAdjust(float value);
 
 private:
-	GLint u_rotationMat;
+	GLint u_hueAdjust;
 };
 
 class SimpleMatrixShader : public ShaderBase