GPUShader: Add GPU_SHADER_2D_IMAGE_MULTISAMPLE_2/4/8/16

This shader is used instead of blitting back and forth to a single sample
buffer.

This means it resolves the color and depth samples and outputs a fragment
which can be depth tested and blended on top of an existing framebuffer.

We do static shader variation with manual loop unrolling for performance
reason. In my test I get 25% more perf with intel integrated gpu and 75%
performance gain with dedicated nvidia card compared to a single shader
with a uniform for sample count.

1 files changed, 67 insertions, 0 deletions

diff --git a/source/blender/gpu/shaders/gpu_shader_image_multisample_resolve_frag.glsl b/source/blender/gpu/shaders/gpu_shader_image_multisample_resolve_frag.glsl
new file mode 100644
index 00000000000..de1fd8b6b58
--- /dev/null
+++ b/source/blender/gpu/shaders/gpu_shader_image_multisample_resolve_frag.glsl
@@ -0,0 +1,67 @@
+
+uniform sampler2DMS depthMulti;
+uniform sampler2DMS colorMulti;
+
+out vec4 fragColor;
+
+#if SAMPLES > 16
+#error "Too many samples"
+#endif
+
+void main()
+{
+	ivec2 texel = ivec2(gl_FragCoord.xy);
+
+	float depth = 1.0;
+	depth = min(depth, texelFetch(depthMulti, texel, 0).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 1).r);
+#if SAMPLES > 2
+	depth = min(depth, texelFetch(depthMulti, texel, 2).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 3).r);
+#endif
+#if SAMPLES > 4
+	depth = min(depth, texelFetch(depthMulti, texel, 4).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 5).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 6).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 7).r);
+#endif
+#if SAMPLES > 8
+	depth = min(depth, texelFetch(depthMulti, texel, 8).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 9).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 10).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 11).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 12).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 13).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 14).r);
+	depth = min(depth, texelFetch(depthMulti, texel, 15).r);
+#endif
+
+	vec4 color = vec4(0.0);
+	color += texelFetch(colorMulti, texel, 0);
+	color += texelFetch(colorMulti, texel, 1);
+#if SAMPLES > 2
+	color += texelFetch(colorMulti, texel, 2);
+	color += texelFetch(colorMulti, texel, 3);
+#endif
+#if SAMPLES > 4
+	color += texelFetch(colorMulti, texel, 4);
+	color += texelFetch(colorMulti, texel, 5);
+	color += texelFetch(colorMulti, texel, 6);
+	color += texelFetch(colorMulti, texel, 7);
+#endif
+#if SAMPLES > 8
+	color += texelFetch(colorMulti, texel, 8);
+	color += texelFetch(colorMulti, texel, 9);
+	color += texelFetch(colorMulti, texel, 10);
+	color += texelFetch(colorMulti, texel, 11);
+	color += texelFetch(colorMulti, texel, 12);
+	color += texelFetch(colorMulti, texel, 13);
+	color += texelFetch(colorMulti, texel, 14);
+	color += texelFetch(colorMulti, texel, 15);
+#endif
+
+	const float inv_samples = 1.0 / float(SAMPLES);
+
+	fragColor = color * inv_samples;
+	gl_FragDepth = depth;
+}