gsdx-ogl: use normalized index coordinate for palette texture

In palette mode, 90% of texture accesses are done in 8 bits.
So let's keep this path as light as possible. It reduces GPU load.

plugins/GSdx/res/glsl/tfx_fs.glsl

@@ -80,9 +80,9 @@ vec4 sample_c(vec2 uv)
 	return texture(TextureSampler, uv);
 }
 
-vec4 sample_p(uint idx)
+vec4 sample_p(float idx)
 {
-	return texelFetch(PaletteSampler, ivec2(idx, 0u), 0);
+	return texture(PaletteSampler, vec2(idx, 0.0f));
 }
 
 vec4 wrapuv(vec4 uv)
@@ -149,7 +149,7 @@ mat4 sample_4c(vec4 uv)
 	return c;
 }
 
-uvec4 sample_4_index(vec4 uv)
+vec4 sample_4_index(vec4 uv)
 {
 	vec4 c;
 
@@ -169,18 +169,22 @@ uvec4 sample_4_index(vec4 uv)
 
 #if PS_IFMT == 1
 	// 4HH
-	return i >> 4u;
+	return vec4(i >> 4u) / 255.0f;
+
 #elif PS_IFMT == 2
 	// 4HL
-	return i & 0xFu;
+	return vec4(i & 0xFu) / 255.0f;
+
 #else
+	// Most of texture will hit this code so keep normalized float value
+
 	// 8 bits
-	return i;
+	return c;
 #endif
 
 }
 
-mat4 sample_4p(uvec4 u)
+mat4 sample_4p(vec4 u)
 {
 	mat4 c;
 

plugins/GSdx/res/glsl_source.h

@@ -939,9 +939,9 @@ static const char* tfx_fs_all_glsl =
 	"	return texture(TextureSampler, uv);\n"
 	"}\n"
 	"\n"
-	"vec4 sample_p(uint idx)\n"
+	"vec4 sample_p(float idx)\n"
 	"{\n"
-	"	return texelFetch(PaletteSampler, ivec2(idx, 0u), 0);\n"
+	"	return texture(PaletteSampler, vec2(idx, 0.0f));\n"
 	"}\n"
 	"\n"
 	"vec4 wrapuv(vec4 uv)\n"
@@ -1008,7 +1008,7 @@ static const char* tfx_fs_all_glsl =
 	"	return c;\n"
 	"}\n"
 	"\n"
-	"uvec4 sample_4_index(vec4 uv)\n"
+	"vec4 sample_4_index(vec4 uv)\n"
 	"{\n"
 	"	vec4 c;\n"
 	"\n"
@@ -1028,18 +1028,22 @@ static const char* tfx_fs_all_glsl =
 	"\n"
 	"#if PS_IFMT == 1\n"
 	"	// 4HH\n"
-	"	return i >> 4u;\n"
+	"	return vec4(i >> 4u) / 255.0f;\n"
+	"\n"
 	"#elif PS_IFMT == 2\n"
 	"	// 4HL\n"
-	"	return i & 0xFu;\n"
+	"	return vec4(i & 0xFu) / 255.0f;\n"
+	"\n"
 	"#else\n"
+	"	// Most of texture will hit this code so keep normalized float value\n"
+	"\n"
 	"	// 8 bits\n"
-	"	return i;\n"
+	"	return c;\n"
 	"#endif\n"
 	"\n"
 	"}\n"
 	"\n"
-	"mat4 sample_4p(uvec4 u)\n"
+	"mat4 sample_4p(vec4 u)\n"
 	"{\n"
 	"	mat4 c;\n"
 	"\n"