Evas GL shaders: Add random noise in the fragment shaderdevs/jpeg/dithering

This small noise, added to the fragment shader's output color, makes
smooth up-scaling of gradient images look very good. Gradient images
that are zoomed in a lot show some banding or blocks, that are
the dithering pixels (good for the original size, terrible when
upscaled).

The simplest solution is to add noise, not even using a proper
dithering pattern. This patch adds noise everytime there is a
texture, without any smart logic. Still looks beautiful.

2 files changed, 38 insertions, 1 deletions

diff --git a/src/modules/evas/engines/gl_common/shader/evas_gl_shaders.x b/src/modules/evas/engines/gl_common/shader/evas_gl_shaders.x
index 558531a50b..dec8aa93bc 100644
--- a/src/modules/evas/engines/gl_common/shader/evas_gl_shaders.x
+++ b/src/modules/evas/engines/gl_common/shader/evas_gl_shaders.x
@@ -26,9 +26,11 @@ static const char fragment_glsl[] =
    "#ifdef SHD_EXTERNAL\n"
    "uniform SAMPLER_EXTERNAL_OES tex;\n"
    "varying vec2 tex_c;\n"
+   "#define ADD_NOISE 1\n"
    "#elif defined(SHD_TEX)\n"
    "uniform sampler2D tex;\n"
    "varying vec2 tex_c;\n"
+   "#define ADD_NOISE 1\n"
    "#endif\n"
    "#if defined(SHD_NV12) || defined(SHD_YUY2)\n"
    "uniform sampler2D texuv;\n"
@@ -80,6 +82,14 @@ static const char fragment_glsl[] =
    "#  endif\n"
    "# endif\n"
    "#endif\n"
+   "#ifdef ADD_NOISE\n"
+   "float rand(vec2 co)\n"
+   "{\n"
+   "   /* Magic 'random' number in range [0..1]. 'co' should be random coordinate.\n"
+   "    * Distribution is not great. Falls apart with lowp float. */\n"
+   "   return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453) - 0.5;\n"
+   "}\n"
+   "#endif\n"
    "void main()\n"
    "{\n"
    "   vec4 c;\n"
@@ -130,6 +140,11 @@ static const char fragment_glsl[] =
    "#else\n"
    "   c = vec4(1, 1, 1, 1);\n"
    "#endif\n"
+   "#ifdef ADD_NOISE\n"
+   "   vec4 noise = vec4(rand(tex_c) / 256.0, rand(tex_c + vec2(1, 1)) / 256.0, rand(tex_c + vec2(2, 2)) / 256.0, 0);\n"
+   "   noise.a = max(noise.r, noise.g);\n"
+   "   noise.a = max(noise.a, noise.b);\n"
+   "#endif\n"
    "#ifdef SHD_MASK\n"
    "   float ma;\n"
    "# if defined(SHD_MASKSAM12) || defined(SHD_MASKSAM21)\n"
@@ -160,6 +175,9 @@ static const char fragment_glsl[] =
    "#ifdef SHD_TEXA\n"
    "     * texture2D(texa, tex_a).r\n"
    "#endif\n"
+   "#ifdef ADD_NOISE\n"
+   "     + noise\n"
+   "#endif\n"
    "   ;\n"
    "}\n";
 
diff --git a/src/modules/evas/engines/gl_common/shader/fragment.glsl b/src/modules/evas/engines/gl_common/shader/fragment.glsl
index b534961300..8436298bfe 100644
--- a/src/modules/evas/engines/gl_common/shader/fragment.glsl
+++ b/src/modules/evas/engines/gl_common/shader/fragment.glsl
@@ -13,9 +13,11 @@ varying vec4 col;
 #ifdef SHD_EXTERNAL
 uniform SAMPLER_EXTERNAL_OES tex;
 varying vec2 tex_c;
+#define ADD_NOISE 1
 #elif defined(SHD_TEX)
 uniform sampler2D tex;
 varying vec2 tex_c;
+#define ADD_NOISE 1
 #endif
 
 #if defined(SHD_NV12) || defined(SHD_YUY2)
@@ -74,6 +76,15 @@ varying vec2 masktex_s[4];
 # endif
 #endif
 
+#ifdef ADD_NOISE
+float rand(vec2 co)
+{
+   /* Magic 'random' number in range [0..1]. 'co' should be random coordinate.
+    * Distribution is not great. Falls apart with lowp float. */
+   return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453) - 0.5;
+}
+#endif
+
 void main()
 {
    vec4 c;
@@ -126,11 +137,16 @@ void main()
 
 #elif defined(SHD_TEX) || defined(SHD_EXTERNAL)
    c = texture2D(tex, tex_c).SWZ;
-
 #else
    c = vec4(1, 1, 1, 1);
 #endif
 
+#ifdef ADD_NOISE
+   vec4 noise = vec4(rand(tex_c) / 256.0, rand(tex_c + vec2(1, 1)) / 256.0, rand(tex_c + vec2(2, 2)) / 256.0, 0);
+   noise.a = max(noise.r, noise.g);
+   noise.a = max(noise.a, noise.b);
+#endif
+
 #ifdef SHD_MASK
    float ma;
 # if defined(SHD_MASKSAM12) || defined(SHD_MASKSAM21)
@@ -163,6 +179,9 @@ void main()
 #ifdef SHD_TEXA
      * texture2D(texa, tex_a).r
 #endif
+#ifdef ADD_NOISE
+     + noise
+#endif
    ;
 }