1 files changed, 131 insertions, 0 deletions
diff --git a/examples/qt3d/wireframe/shaders/robustwireframe.geom b/examples/qt3d/wireframe/shaders/robustwireframe.geom
new file mode 100644
index 000000000..6eb0ecc76
--- /dev/null
+++ b/examples/qt3d/wireframe/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();
+    }
+}