Simulations - Practical Rendering and Computation with Direct3D 11 - page 567

With the particle data introduced into the pipeline, we can now render the individual
point primitives in the locations of each particle. However, this would be a fairly unsuitable
technique for rendering the particle system, since each particle could only occupy a single
pixel of the output render target. Instead, we will use the geometry shader to expand our
individual point primitives into two triangles that form a quad. The shader program for this
operation is shown in Listing 12.12.

cbuffer ParticleRenderParameters
{

float4 EmitterLocationj
float4 ConsumerLocation;

};

static const float4 g_positions[4] =
{

float4( -1, 1, 0, 0 ),
float4( 1, 1, 0, 0 ),
float4( -1, -1, 0, 0 ),
float4( 1, -1, 0, 0 ),

};

static const float2 g_texcoords[4] =
{

float2( 0, 1 ),
float2( 1, 1 ),
float2( 0, 0 ),
float2( 1, 0 ),

};

[maxvertexcount(4) ]
void 6SMAIN( point GS_INPUT input[1], inout TriangleStream<PS_INPUT>
SpriteStream )
{

PS_INPUT output;

float dist = saturate( length( input[0] .position - ConsumerLocation.xyz )
/ 100.0f );

float4 color = float4( 0.2f, 0.2f, 1 .0f, 0.0f ) * ( dist )

+ float4( 1.0f, 0.2f, 0.2f, 0.0f ) * ( 1.0f - dist );

// Transform to view space
float4 viewposition = mul( float4( input[0].position, 1.0 f ),
WorldViewMatrix );

// Emit two new triangles
for ( int i =0; i < 4; i++ )
{

// Transform to clip space
output.position = mul( viewposition + g_positions[i] , ProjMatrix );
output.texcoords = g_texcoords[i];
output.color = color;