robustwireframe.geom Example File | Qt 3D 5.12.12

- Qt 5.12
- Qt 3D
- Qt 3D: Wireframe QML Example
- robustwireframe.geom Example File
- Qt 5.12.12 Reference Documentation

# robustwireframe.geom Example File

wireframe/shaders/robustwireframe.geom

     #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();
         }
     }