add bayer 4x4 matrix ordered grid dithering shader

Features:
- uses bayer 4x4 matrix
- color depth can be selected with a parameter
- dithering will be calculated according to selected color depth

dithering/bayer_4x4.slangp

@@ -0,0 +1,10 @@
+shaders = "1"
+shader0 = "shaders/bayer_4x4.slang"
+filter_linear0 = "false"
+scale_type0 = viewport
+
+parameters = "COLOR_DEPTH;DITHER_TUNE;EGA_PALETTE"
+COLOR_DEPTH = "2.0"
+DITHER_TUNE = "0.0"
+EGA_PALETTE = "0.0"
+

dithering/shaders/bayer_4x4.slang

@@ -0,0 +1,214 @@
+#version 450
+/* 
+ * gizmo98 bayer 4x4 dithering shader
+ * Copyright (C) 2023 gizmo98
+ *
+ *   This program is free software; you can redistribute it and/or modify it
+ *   under the terms of the GNU General Public License as published by the Free
+ *   Software Foundation; either version 2 of the License, or (at your option)
+ *   any later version.
+ *
+ * version 0.1, 16.05.2023
+ * ---------------------------------------------------------------------------------------
+ * - initial commit
+ * 
+ * https://github.com/gizmo98/gizmo-crt-shader
+ *
+ * uses parts of texture anti-aliasing shader from Ikaros https://www.shadertoy.com/view/ldsSRX
+ */
+
+layout(push_constant) uniform Push
+{
+	vec4 SourceSize;
+	vec4 OriginalSize;
+	vec4 OutputSize;
+	uint FrameCount;
+	float COLOR_DEPTH;
+	float DITHER_TUNE;
+	float EGA_PALETTE;
+} params;
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+	mat4 MVP;
+} global;
+
+#pragma parameter COLOR_DEPTH "Color depth in Bits"            1.0 1.0 8.0 1.0
+#pragma parameter DITHER_TUNE "Tune dithering"                 0.0 -64.0 64.0 1.0
+#pragma parameter EGA_PALETTE "EGA palette"                    0.0 0.0 1.0 1.0
+
+#pragma stage vertex
+layout(location = 0) in vec4 Position;
+layout(location = 1) in vec2 TexCoord;
+layout(location = 0) out vec2 vTexCoord;
+
+void main()
+{
+   gl_Position = global.MVP * Position;
+   vTexCoord = TexCoord;
+}
+
+#pragma stage fragment
+layout(location = 0) in vec2 vTexCoord;
+layout(location = 0) out vec4 FragColor;
+layout(set = 0, binding = 2) uniform sampler2D Source;
+
+vec4 DitherPattern(vec4 col, vec2 coord)
+{
+    mat4 bayerMatrix; 
+    bayerMatrix[0] = vec4(0.0, 8.0, 2.0, 10.0);
+    bayerMatrix[1] = vec4(12.0, 4.0, 14.0, 6.0);
+    bayerMatrix[2] = vec4(3.0, 11.0, 1.0, 9.0);
+    bayerMatrix[3] = vec4(15.0, 7.0, 13.0, 5.0);
+    
+    ivec2 st = ivec2(fract(coord.xy / 4.0) * 4.0);
+    float threshold = bayerMatrix[st.x][st.y];
+    float multiplier = pow(2.0,8.0 - params.COLOR_DEPTH) - 1.0;
+    
+    threshold = (threshold / 15.0) - 0.5;
+    threshold *= ((multiplier + params.DITHER_TUNE) / 255.0);
+        
+    col.rgb += threshold; 				           
+    return col;
+}
+
+vec2 saturateA(in vec2 x)
+{
+    return clamp(x, 0.0, 1.0);
+}
+
+vec2 magnify(in vec2 uv, in vec2 res)
+{
+    uv *= res; 
+    return (saturateA(fract(uv) / saturateA(fwidth(uv))) + floor(uv) - 0.5) / res.xy;
+}
+vec4 textureAA(in vec2 uv){
+    vec2 texSize = vec2(textureSize(Source, 0));
+    uv = magnify(uv,texSize.xy);
+    vec2 uv1 = uv*texSize.xy;
+
+    vec2 iuv = floor(uv1);
+    vec4 col = texture( Source, uv );
+    
+    col = DitherPattern( col , iuv - 0.5);
+    return col;
+}
+
+vec4 ColorDepthReduction(vec4 col)
+{
+    float divider = pow(2.0,params.COLOR_DEPTH) - 1.0; 
+    col.rgb *= divider;
+    col.rgb = floor(col.rgb) + step(0.5, fract(col.rgb));
+    col.rgb /= divider;
+    return col;
+}
+
+vec4 EGAPalette(vec4 col)
+{    
+    float divider = 3.0;
+    vec3 c = floor(col.rgb * divider) + step(0.5, fract(col.rgb * divider));
+    if (c.rgb == vec3(0.0,0.0,0.0) ||
+        c.rgb == vec3(1.0,1.0,1.0) || 
+        c.rgb == vec3(2.0,2.0,2.0) ||
+        c.rgb == vec3(3.0,3.0,3.0) ||
+        c.rgb == vec3(2.0,1.0,0.0))
+        col.rgb = col.rgb;
+    // bright green
+    else if (c.rgb == vec3(0.0,3.0,0.0)||
+             c.rgb == vec3(0.0,3.0,2.0)||
+             c.rgb == vec3(2.0,3.0,0.0)||
+             c.rgb == vec3(0.0,3.0,1.0)||
+             c.rgb == vec3(1.0,3.0,1.0)||
+             c.rgb == vec3(1.0,3.0,0.0)||
+             c.rgb == vec3(2.0,3.0,1.0)||
+             c.rgb == vec3(2.0,3.0,2.0))
+        col.rgb = vec3(1.0,3.0,1.0) / divider;
+    // green  
+    else if (c.rgb == vec3(0.0,2.0,0.0)||
+             c.rgb == vec3(0.0,2.0,1.0)||
+             c.rgb == vec3(0.0,1.0,0.0)||
+             c.rgb == vec3(0.0,1.0,1.0)||
+             c.rgb == vec3(1.0,2.0,1.0)||
+             c.rgb == vec3(1.0,2.0,0.0)||
+             c.rgb == vec3(0.0,1.0,1.0))
+        col.rgb = vec3(0.0,2.0,0.0) / divider; 
+    // bright red
+    else if (c.rgb == vec3(3.0,0.0,0.0)||
+             c.rgb == vec3(3.0,0.0,1.0)||
+             c.rgb == vec3(3.0,1.0,0.0)||
+             c.rgb == vec3(3.0,1.0,1.0))
+        col.rgb = vec3(3.0,1.0,1.0) / divider;
+    // red  
+    else if (c.rgb == vec3(2.0,0.0,0.0)||
+             c.rgb == vec3(2.0,0.0,1.0)||
+             c.rgb == vec3(1.0,0.0,0.0))
+        col.rgb = vec3(2.0,0.0,0.0) / divider; 
+    // bright cyan
+    else if (c.rgb == vec3(0.0,3.0,3.0)||
+             c.rgb == vec3(1.0,3.0,3.0)||
+             c.rgb == vec3(2.0,3.0,3.0))
+        col.rgb = vec3(1.0,3.0,3.0) / divider;
+    // cyan
+    else if (c.rgb == vec3(0.0,2.0,2.0)||
+             c.rgb == vec3(1.0,2.0,2.0))
+        col.rgb = vec3(0.0,2.0,2.0) / divider;
+    // bright blue
+    else if (c.rgb == vec3(0.0,2.0,3.0)||
+             c.rgb == vec3(1.0,2.0,3.0)||
+             c.rgb == vec3(0.0,0.0,3.0))
+        col.rgb = vec3(1.0,1.0,3.0) / divider;
+    // blue  
+    else if (c.rgb == vec3(0.0,0.0,2.0)||
+             c.rgb == vec3(0.0,0.0,1.0)||
+             c.rgb == vec3(0.0,1.0,2.0)||
+             c.rgb == vec3(1.0,1.0,3.0)||
+             c.rgb == vec3(0.0,1.0,3.0))
+        col.rgb = vec3(0.0,0.0,2.0) / divider; 
+    // brown  
+    else if (c.rgb == vec3(2.0,1.0,0.0)||
+             c.rgb == vec3(2.0,1.0,1.0)||
+             c.rgb == vec3(1.0,1.0,0.0))
+        col.rgb = vec3(2.0,1.0,0.0) / divider; 
+    // bright yellow  
+    else if (c.rgb == vec3(3.0,3.0,0.0)||
+             c.rgb == vec3(3.0,3.0,1.0)||
+             c.rgb == vec3(3.0,3.0,2.0)||
+             c.rgb == vec3(2.0,2.0,0.0)||
+             c.rgb == vec3(2.0,2.0,1.0))
+        col.rgb = vec3(3.0,3.0,1.0) / divider; 
+    // magenta  
+    else if (c.rgb == vec3(2.0,0.0,2.0)||
+             c.rgb == vec3(2.0,0.0,3.0)||
+             c.rgb == vec3(2.0,1.0,2.0)||
+             c.rgb == vec3(2.0,1.0,3.0))
+        col.rgb = vec3(2.0,0.0,2.0) / divider;     
+    // bright magenta  
+    else if (c.rgb == vec3(3.0,0.0,2.0)||
+             c.rgb == vec3(3.0,0.0,3.0)||
+             c.rgb == vec3(3.0,2.0,3.0)||
+             c.rgb == vec3(3.0,1.0,3.0)||
+             c.rgb == vec3(3.0,1.0,2.0))
+        col.rgb = vec3(3.0,1.0,3.0) / divider; 
+    else if (c.r == 0.0)
+        col.gb = step(2.0,c.gb) * 2.0 / divider;
+    else if (c.g == 0.0)
+        col.rb = step(2.0,c.rb) * 2.0 / divider;
+    else if (c.b == 0.0)
+        col.rg = step(2.0,c.rg) * 2.0 / divider;
+    else if (c.r == 3.0)
+        col.gb = step(1.0,c.gb) / divider;
+    else if (c.g == 3.0)
+        col.rb = step(1.0,c.rb) / divider;
+    else if (c.b == 3.0)
+        col.rg = step(1.0,c.rg) / divider;
+    return col;
+}
+
+void main()
+{
+    vec2 texcoord = vTexCoord.xy;
+    FragColor = textureAA(texcoord);
+    FragColor = ColorDepthReduction(FragColor);
+    if (params.EGA_PALETTE == 1.0)
+        FragColor = EGAPalette(FragColor);
+}