HSV shift

shader/hue.frag

@@ -1,48 +1,36 @@
 
-uniform sampler2D inputTexture;
-uniform float hueAdjust;
+uniform sampler2D texture;
+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 ()
 {
-	const vec4  kRGBToYPrime = vec4 (0.299, 0.587, 0.114, 0.0);
-	const vec4  kRGBToI      = vec4 (0.596, -0.275, -0.321, 0.0);
-	const vec4  kRGBToQ      = vec4 (0.212, -0.523, 0.311, 0.0);
+	vec4 color = texture2D (texture, v_texCoord.xy);
+	vec3 hsv = rgb2hsv(color.rgb);
 
-	const vec4  kYIQToR      = vec4 (1.0, 0.956, 0.621, 0.0);
-	const vec4  kYIQToG      = vec4 (1.0, -0.272, -0.647, 0.0);
-	const vec4  kYIQToB      = vec4 (1.0, -1.107, 1.704, 0.0);
+	hsv.x += hueAdjust;
+	color.rgb = hsv2rgb(hsv);
 
-	/* Sample the input pixel */
-	vec4    color   = texture2D (inputTexture, v_texCoord.xy);
-
-	/* Convert to YIQ */
-	float   YPrime  = dot (color, kRGBToYPrime);
-	float   I       = dot (color, kRGBToI);
-	float   Q       = dot (color, kRGBToQ);
-
-	/* Calculate the hue and chroma */
-	float   hue     = atan (Q, I);
-	float   chroma  = sqrt (I * I + Q * Q);
-
-	/* Make the user's adjustments */
-	hue += hueAdjust;
-
-	/* Remember old I and color */
-	float IOriginal = I;
-	vec4 coOriginal = color;
-
-	/* Convert back to YIQ */
-	Q = chroma * sin (hue);
-	I = chroma * cos (hue);
-
-	/* Convert back to RGB */
-	vec4 yIQ = vec4 (YPrime, I, Q, 0.0);
-	color.r  = dot  (yIQ, kYIQToR);
-	color.g  = dot  (yIQ, kYIQToG);
-	color.b  = dot  (yIQ, kYIQToB);
-
-	/* Save the result */
-	gl_FragColor = (IOriginal == 0.0) ? coOriginal : color;
+	gl_FragColor = color;
 }

src/bitmap.cpp

@@ -854,13 +854,10 @@ void Bitmap::hueChange(int hue)
 	quad.setTexPosRect(texRect, texRect);
 	quad.setColor(Vec4(1, 1, 1, 1));
 
-	/* Calculate hue parameter */
-	hue = wrapRange(hue, 0, 359);
-	float hueAdj = -((M_PI * 2) / 360) * hue;
-
 	HueShader &shader = shState->shaders().hue;
 	shader.bind();
-	shader.setHueAdjust(hueAdj);
+	/* Shader expects normalized value */
+	shader.setHueAdjust(wrapRange(hue, 0, 359) / 360.0f);
 
 	FBO::bind(newTex.fbo);
 	p->pushSetViewport(shader);

src/shader.cpp

@@ -551,7 +551,6 @@ HueShader::HueShader()
 	ShaderBase::init();
 
 	GET_U(hueAdjust);
-	GET_U(inputTexture);
 }
 
 void HueShader::setHueAdjust(float value)
@@ -559,11 +558,6 @@ void HueShader::setHueAdjust(float value)
 	gl.Uniform1f(u_hueAdjust, value);
 }
 
-void HueShader::setInputTexture(TEX::ID tex)
-{
-	setTexUniform(u_inputTexture, 0, tex);
-}
-
 
 SimpleMatrixShader::SimpleMatrixShader()
 {

src/shader.h

@@ -241,10 +241,9 @@ public:
 	HueShader();
 
 	void setHueAdjust(float value);
-	void setInputTexture(TEX::ID tex);
 
 private:
-	GLint u_hueAdjust, u_inputTexture;
+	GLint u_hueAdjust;
 };
 
 class SimpleMatrixShader : public ShaderBase