robustwireframe.geom Example File | Qt 3D 5.9

Qt 5.9 | Qt 3D | Qt 3D: Wireframe QML Example | robustwireframe.geom Example File

Qt 5.9.9 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();
          }
      }