- Qt 5.5
- Qt3D Module
- Qt3D: Wireframe QML Example
- robustwireframe.geom Example File
- Qt 5.5.1 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();
        }
    }