60 lines
2.1 KiB
GLSL
60 lines
2.1 KiB
GLSL
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/* Adaptation of Conservative Rasterization
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* from GPU Gems 2
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* Using method 2.
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*
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* Actual final implementation does not do conservative rasterization and only
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* avoids triangles producing no fragments.
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*/
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layout(triangles) in;
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layout(triangle_strip, max_vertices = 3) out;
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RESOURCE_ID_VARYING
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uniform vec2 sizeViewport;
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uniform vec2 sizeViewportInv;
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void main()
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{
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/* Compute plane normal in ndc space. */
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vec3 pos0 = gl_in[0].gl_Position.xyz / gl_in[0].gl_Position.w;
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vec3 pos1 = gl_in[1].gl_Position.xyz / gl_in[1].gl_Position.w;
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vec3 pos2 = gl_in[2].gl_Position.xyz / gl_in[2].gl_Position.w;
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vec3 plane = normalize(cross(pos1 - pos0, pos2 - pos0));
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/* Compute NDC bound box. */
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vec4 bbox = vec4(min(min(pos0.xy, pos1.xy), pos2.xy), max(max(pos0.xy, pos1.xy), pos2.xy));
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/* Convert to pixel space. */
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bbox = (bbox * 0.5 + 0.5) * sizeViewport.xyxy;
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/* Detect failure cases where triangles would produce no fragments. */
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bvec2 is_subpixel = lessThan(bbox.zw - bbox.xy, vec2(1.0));
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/* View aligned triangle. */
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const float threshold = 0.00001;
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bool is_coplanar = abs(plane.z) < threshold;
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for (int i = 0; i < 3; i++) {
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gl_Position = gl_in[i].gl_Position;
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if (all(is_subpixel)) {
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vec2 ofs = (i == 0) ? vec2(-1.0) : ((i == 1) ? vec2(2.0, -1.0) : vec2(-1.0, 2.0));
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/* HACK: Fix cases where the triangle is too small make it cover at least one pixel. */
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gl_Position.xy += sizeViewportInv.xy * gl_Position.w * ofs;
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}
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/* Test if the triangle is almost parralele with the view to avoid precision issues. */
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else if (any(is_subpixel) || is_coplanar) {
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/* HACK: Fix cases where the triangle is Parallel to the view by deforming it slightly. */
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vec2 ofs = (i == 0) ? vec2(-1.0) : ((i == 1) ? vec2(1.0, -1.0) : vec2(1.0));
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gl_Position.xy += sizeViewportInv.xy * gl_Position.w * ofs;
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}
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else {
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/* Triangle expansion should happen here, but we decide to not implement it for
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* depth precision & performance reasons. */
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}
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#ifdef USE_WORLD_CLIP_PLANES
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world_clip_planes_set_clip_distance(gl_in[i].gl_ClipDistance);
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#endif
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EmitVertex();
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}
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EndPrimitive();
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}
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