initial commit, 4.5 stable

modules/betsy/alpha_stitch.glsl

@@ -0,0 +1,21 @@
+// RGB and Alpha components of ETC2 RGBA/DXT5 are computed separately.
+// This compute shader merely stitches them together to form the final result
+// It's also used by RG11/BC4 driver to stitch two R11/BC4 into one RG11/BC5
+
+#[compute]
+#version 450
+
+layout(local_size_x = 8, //
+		local_size_y = 8, //
+		local_size_z = 1) in;
+
+layout(binding = 0) uniform usampler2D srcRGB;
+layout(binding = 1) uniform usampler2D srcAlpha;
+layout(binding = 2, rgba32ui) uniform restrict writeonly uimage2D dstTexture;
+
+void main() {
+	uvec2 rgbBlock = texelFetch(srcRGB, ivec2(gl_GlobalInvocationID.xy), 0).xy;
+	uvec2 alphaBlock = texelFetch(srcAlpha, ivec2(gl_GlobalInvocationID.xy), 0).xy;
+
+	imageStore(dstTexture, ivec2(gl_GlobalInvocationID.xy), uvec4(rgbBlock.xy, alphaBlock.xy));
+}