evas gl - experiment with dithered gl rendering

this adds a dither func (4x4 dither matrix) to experiment with higher
quality rendering in gl - this assumes you have a normal 8bit per
channel buffer for now (99% of people) and will approximate values in
between the 256 steps 8 bits provides by using the dither matrix based
on gl_FragCoord position. it's just a flag in the shader flags for now
so can be turned on/off in code. this definitely makes blurs look much
better... everything else seems basicall the same. let's see how this
goes.

@feat

4 files changed, 113 insertions, 9 deletions

diff --git a/src/modules/evas/engines/gl_common/evas_gl_shader.c b/src/modules/evas/engines/gl_common/evas_gl_shader.c
index 99b104f651..2f1388056d 100644
--- a/src/modules/evas/engines/gl_common/evas_gl_shader.c
+++ b/src/modules/evas/engines/gl_common/evas_gl_shader.c
@@ -13,9 +13,9 @@
 #define I(p) ((int)(intptr_t)p)
 
 #ifdef WORDS_BIGENDIAN
-# define BASEFLAG SHADER_FLAG_BIGENDIAN
+# define BASEFLAG SHADER_FLAG_DITHER | SHADER_FLAG_BIGENDIAN
 #else
-# define BASEFLAG 0
+# define BASEFLAG SHADER_FLAG_DITHER
 #endif
 
 typedef enum {
@@ -47,8 +47,9 @@ typedef enum {
    SHADER_FLAG_FILTER_ALPHA_ONLY = (1 << 25),
    SHADER_FLAG_FILTER_GRAYSCALE  = (1 << 26),
    SHADER_FLAG_FILTER_INVERSE_COLOR  = (1 << 27),
+   SHADER_FLAG_DITHER            = (1 << 28),
 } Shader_Flag;
-#define SHADER_FLAG_COUNT 28
+#define SHADER_FLAG_COUNT 29
 
 static const char *_shader_flags[SHADER_FLAG_COUNT] = {
    "TEX",
@@ -79,6 +80,7 @@ static const char *_shader_flags[SHADER_FLAG_COUNT] = {
    "ALPHA_ONLY",
    "FILTER_GRAYSCALE",
    "FILTER_INVERSE_COLOR",
+   "DITHER",
 };
 
 static Eina_Bool compiler_released = EINA_FALSE;
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 d244b37f08..b534f66c41 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
@@ -98,6 +98,33 @@ static const char fragment_glsl[] =
    "uniform float blur_div;\n"
    "#endif\n"
    "// ----------------------------------------------------------------------------\n"
+   "#ifdef SHD_DITHER\n"
+   "const mat4 dm = mat4(vec4( 0,  8,  2, 10),\n"
+   "                     vec4(12,  4, 14,  6),\n"
+   "                     vec4( 3, 11,  1,  9),\n"
+   "                     vec4(15,  7, 13,  5));\n"
+   "float dither_closest(vec2 pos, float val)\n"
+   "{\n"
+   "   float limit = dm[int(pos.x)][int(pos.y)] / 16.0;\n"
+   "   if (val <= limit) return 0.0;\n"
+   "   return 1.0;\n"
+   "}\n"
+   "float dither_8bit(vec2 modpos, float val)\n"
+   "{\n"
+   "   float val_quant = float(floor(val * 255.0)) / 255.0;\n"
+   "   float val_delta = (val - val_quant) / (1.0 / 256.0);\n"
+   "   float val_roundup = dither_closest(modpos, val_delta);\n"
+   "   return val_quant + (val_roundup * (1.0 / 256.0));\n"
+   "}\n"
+   "vec4 dither(vec4 col, vec2 pos)\n"
+   "{\n"
+   "   vec2 modpos = vec2(mod(float(pos.x), 4.0), mod(float(pos.y), 4.0));\n"
+   "   return vec4(dither_8bit(modpos, col.r),\n"
+   "               dither_8bit(modpos, col.g),\n"
+   "               dither_8bit(modpos, col.b),\n"
+   "               dither_8bit(modpos, col.a));\n"
+   "}\n"
+   "#endif\n"
    "#ifndef SHD_FILTER_BLUR\n"
    "void main()\n"
    "{\n"
@@ -220,10 +247,13 @@ static const char fragment_glsl[] =
    "   c.b = c.r;\n"
    "#endif\n"
    "#ifdef SHD_FILTER_INVERSE_COLOR\n"
-   "   c.rgb = c.a - c.rgb;\n"
+   "   c.rgb = c.a - c.rgba;\n"
    "#endif\n"
    "#ifndef SHD_FILTER_BLUR\n"
    "   gl_FragColor =\n"
+   "#ifdef SHD_DITHER\n"
+   "   dither(\n"
+   "#endif\n"
    "       c\n"
    "#ifndef SHD_NOMUL\n"
    "     * col\n"
@@ -234,6 +264,9 @@ static const char fragment_glsl[] =
    "#ifdef SHD_FILTER_DISPLACE\n"
    "     * fa\n"
    "#endif\n"
+   "#ifdef SHD_DITHER\n"
+   "   , gl_FragCoord.xy)\n"
+   "#endif\n"
    "   ;\n"
    "}\n"
    "#else // SHD_FILTER_BLUR\n"
@@ -278,9 +311,25 @@ static const char fragment_glsl[] =
    "      acc += (px1 + px2) * weight;\n"
    "   }\n"
    "#ifndef SHD_NOMUL\n"
-   "   gl_FragColor = (acc / blur_div) * col;\n"
+   "   gl_FragColor =\n"
+   "#ifdef SHD_DITHER\n"
+   "     dither(\n"
+   "#endif\n"
+   "            (acc / blur_div) * col, gl_FragCoord.xy\n"
+   "#ifdef SHD_DITHER\n"
+   "           )\n"
+   "#endif\n"
+   "   ;\n"
    "#else\n"
-   "   gl_FragColor = (acc / blur_div);\n"
+   "   gl_FragColor =\n"
+   "#ifdef SHD_DITHER\n"
+   "     dither(\n"
+   "#endif\n"
+   "            (acc / blur_div), gl_FragCoord.xy\n"
+   "#ifdef SHD_DITHER\n"
+   "           )\n"
+   "#endif\n"
+   "   ;\n"
    "#endif\n"
    "}\n"
    "#endif // SHD_FILTER_BLUR\n";
diff --git a/src/modules/evas/engines/gl_common/shader/fragment.glsl b/src/modules/evas/engines/gl_common/shader/fragment.glsl
index 09947968e9..b715c8de99 100644
--- a/src/modules/evas/engines/gl_common/shader/fragment.glsl
+++ b/src/modules/evas/engines/gl_common/shader/fragment.glsl
@@ -97,6 +97,37 @@ uniform float blur_div;
 
 // ----------------------------------------------------------------------------
 
+#ifdef SHD_DITHER
+const mat4 dm = mat4(vec4( 0,  8,  2, 10),
+                     vec4(12,  4, 14,  6),
+                     vec4( 3, 11,  1,  9),
+                     vec4(15,  7, 13,  5));
+
+float dither_closest(vec2 pos, float val)
+{
+   float limit = dm[int(pos.x)][int(pos.y)] / 16.0;
+   if (val <= limit) return 0.0;
+   return 1.0;
+}
+
+float dither_8bit(vec2 modpos, float val)
+{
+   float val_quant = float(floor(val * 255.0)) / 255.0;
+   float val_delta = (val - val_quant) / (1.0 / 256.0);
+   float val_roundup = dither_closest(modpos, val_delta);
+   return val_quant + (val_roundup * (1.0 / 256.0));
+}
+
+vec4 dither(vec4 col, vec2 pos)
+{
+   vec2 modpos = vec2(mod(float(pos.x), 4.0), mod(float(pos.y), 4.0));
+   return vec4(dither_8bit(modpos, col.r),
+               dither_8bit(modpos, col.g),
+               dither_8bit(modpos, col.b),
+               dither_8bit(modpos, col.a));
+}
+#endif
+
 #ifndef SHD_FILTER_BLUR
 void main()
 {
@@ -243,6 +274,9 @@ vec4 fetch_pixel(float ox, float oy)
 #ifndef SHD_FILTER_BLUR
 
    gl_FragColor =
+#ifdef SHD_DITHER
+   dither(
+#endif
        c
 #ifndef SHD_NOMUL
      * col
@@ -253,6 +287,9 @@ vec4 fetch_pixel(float ox, float oy)
 #ifdef SHD_FILTER_DISPLACE
      * fa
 #endif
+#ifdef SHD_DITHER
+   , gl_FragCoord.xy)
+#endif
    ;
 }
 
@@ -312,9 +349,25 @@ void main()
    }
 
 #ifndef SHD_NOMUL
-   gl_FragColor = (acc / blur_div) * col;
+   gl_FragColor =
+#ifdef SHD_DITHER
+     dither(
+#endif
+            (acc / blur_div) * col, gl_FragCoord.xy
+#ifdef SHD_DITHER
+           )
+#endif
+   ;
 #else
-   gl_FragColor = (acc / blur_div);
+   gl_FragColor =
+#ifdef SHD_DITHER
+     dither(
+#endif
+            (acc / blur_div), gl_FragCoord.xy
+#ifdef SHD_DITHER
+           )
+#endif
+   ;
 #endif
 }
 
diff --git a/src/modules/evas/engines/gl_common/shader/gen_shaders.sh b/src/modules/evas/engines/gl_common/shader/gen_shaders.sh
index 7c2fec1e47..c477ee4dbe 100755
--- a/src/modules/evas/engines/gl_common/shader/gen_shaders.sh
+++ b/src/modules/evas/engines/gl_common/shader/gen_shaders.sh
@@ -3,7 +3,7 @@
 # This script will generate a C file containing all the shaders used by Evas
 
 DIR=`dirname $0`
-cd $DIR/../../../../../
+#cd $DIR/../../../../../
 
 OUTPUT="$DIR/evas_gl_shaders.x"