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Diffstat (limited to 'examples/qt3d/wave/shaders/robustwireframe.geom')
-rw-r--r-- | examples/qt3d/wave/shaders/robustwireframe.geom | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/examples/qt3d/wave/shaders/robustwireframe.geom b/examples/qt3d/wave/shaders/robustwireframe.geom new file mode 100644 index 000000000..6eb0ecc76 --- /dev/null +++ b/examples/qt3d/wave/shaders/robustwireframe.geom @@ -0,0 +1,131 @@ +#version 330 core + +layout( triangles ) in; +layout( triangle_strip, max_vertices = 3 ) out; + +in EyeSpaceVertex { + vec3 position; + vec3 normal; +} gs_in[]; + +out WireframeVertex { + vec3 position; + vec3 normal; + noperspective vec4 edgeA; + noperspective vec4 edgeB; + flat int configuration; +} gs_out; + +uniform mat4 viewportMatrix; + +const int infoA[] = int[]( 0, 0, 0, 0, 1, 1, 2 ); +const int infoB[] = int[]( 1, 1, 2, 0, 2, 1, 2 ); +const int infoAd[] = int[]( 2, 2, 1, 1, 0, 0, 0 ); +const int infoBd[] = int[]( 2, 2, 1, 2, 0, 2, 1 ); + +vec2 transformToViewport( const in vec4 p ) +{ + return vec2( viewportMatrix * ( p / p.w ) ); +} + +void main() +{ + gs_out.configuration = int(gl_in[0].gl_Position.z < 0) * int(4) + + int(gl_in[1].gl_Position.z < 0) * int(2) + + int(gl_in[2].gl_Position.z < 0); + + // If all vertices are behind us, cull the primitive + if (gs_out.configuration == 7) + return; + + // Transform each vertex into viewport space + vec2 p[3]; + p[0] = transformToViewport( gl_in[0].gl_Position ); + p[1] = transformToViewport( gl_in[1].gl_Position ); + p[2] = transformToViewport( gl_in[2].gl_Position ); + + if (gs_out.configuration == 0) + { + // Common configuration where all vertices are within the viewport + gs_out.edgeA = vec4(0.0); + gs_out.edgeB = vec4(0.0); + + // Calculate lengths of 3 edges of triangle + float a = length( p[1] - p[2] ); + float b = length( p[2] - p[0] ); + float c = length( p[1] - p[0] ); + + // Calculate internal angles using the cosine rule + float alpha = acos( ( b * b + c * c - a * a ) / ( 2.0 * b * c ) ); + float beta = acos( ( a * a + c * c - b * b ) / ( 2.0 * a * c ) ); + + // Calculate the perpendicular distance of each vertex from the opposing edge + float ha = abs( c * sin( beta ) ); + float hb = abs( c * sin( alpha ) ); + float hc = abs( b * sin( alpha ) ); + + // Now add this perpendicular distance as a per-vertex property in addition to + // the position and normal calculated in the vertex shader. + + // Vertex 0 (a) + gs_out.edgeA = vec4( ha, 0.0, 0.0, 0.0 ); + gs_out.normal = gs_in[0].normal; + gs_out.position = gs_in[0].position; + gl_Position = gl_in[0].gl_Position; + EmitVertex(); + + // Vertex 1 (b) + gs_out.edgeA = vec4( 0.0, hb, 0.0, 0.0 ); + gs_out.normal = gs_in[1].normal; + gs_out.position = gs_in[1].position; + gl_Position = gl_in[1].gl_Position; + EmitVertex(); + + // Vertex 2 (c) + gs_out.edgeA = vec4( 0.0, 0.0, hc, 0.0 ); + gs_out.normal = gs_in[2].normal; + gs_out.position = gs_in[2].position; + gl_Position = gl_in[2].gl_Position; + EmitVertex(); + + // Finish the primitive off + EndPrimitive(); + } + else + { + // Viewport projection breaks down for one or two vertices. + // Caclulate what we can here and defer rest to fragment shader. + // Since this is coherent for the entire primitive the conditional + // in the fragment shader is still cheap as all concurrent + // fragment shader invocations will take the same code path. + + // Copy across the viewport-space points for the (up to) two vertices + // in the viewport + gs_out.edgeA.xy = p[infoA[gs_out.configuration]]; + gs_out.edgeB.xy = p[infoB[gs_out.configuration]]; + + // Copy across the viewport-space edge vectors for the (up to) two vertices + // in the viewport + gs_out.edgeA.zw = normalize( gs_out.edgeA.xy - p[ infoAd[gs_out.configuration] ] ); + gs_out.edgeB.zw = normalize( gs_out.edgeB.xy - p[ infoBd[gs_out.configuration] ] ); + + // Pass through the other vertex attributes + gs_out.normal = gs_in[0].normal; + gs_out.position = gs_in[0].position; + gl_Position = gl_in[0].gl_Position; + EmitVertex(); + + gs_out.normal = gs_in[1].normal; + gs_out.position = gs_in[1].position; + gl_Position = gl_in[1].gl_Position; + EmitVertex(); + + gs_out.normal = gs_in[2].normal; + gs_out.position = gs_in[2].position; + gl_Position = gl_in[2].gl_Position; + EmitVertex(); + + // Finish the primitive off + EndPrimitive(); + } +} |