Multithreaded Paraboloid Mapping - Practical Rendering and Computation with Direct3D 11 - page 581

winding order is flipped. This effectively reverses the prior situation, and clips or culls the
positive half-space geometry. In this way, we only apply the appropriate sets of geometry
to each of the paraboloid maps.
[maxvertexcount(3) ]
[instance(2)]
void GSMAIN( triangle GS_INPUT input[3],
uint id : SV_GSInstanceID,
inout TriangleStream<PS_INPUT> OutputStream )
{
PS_INPUT output;
// Initialize the vertex order and the direction of the paraboloid.
uint3 order = uint3( 0, 1, 2 );
float direction = 1.0f;
// Check to see which copy of the primitive this is. If it is 0, then it
// is considered the front facing paraboloid. If it is 1, then it is
// considered the back facing paraboloid. For back facing, we reverse
// the output vertex winding order,
if ( id == 1 )
{
order. xyz = order.xzy;
direction = -1.0f;
}
// Emit three vertices for one complete triangle,
for ( int i = 6; i < 3; i++ )
{
// Create a projection factor, which determines which half space
// will be considered positive and also adds the viewing vector
// which is (0,0,1) and hence can only be added to the z-component.
float projFactor = input[order[i]] .z_value * direction + 1.0f;
output. position.x = input[order[i]].position.x / projFactor;
output. position.y = input[order[i]] .position. y / projFactor;
output.position. z = input[order[i]] .position. z;
output.position. w = 1.0f;
// Simply use the geometry shader instance as the render target
// index for this primitive,
output.rtindex = id;
// Pass through the texture coordinates to the pixel shader
output.tex = input[order[i] ] .tex;
output. z_value = input[order[i] ] .z_value * direction;
// Write the vertex to the output stream.
OutputStream. Append(output);
}
OutputStream. RestartStrip( );
}
Listing 13.2. The geometry shader for rendering a textured object into dual paraboloid maps.