I'm writing a shader which takes particles as points and expands it into 4 vertices. I'm doing this by adding to xy in the geometry shader for the 4 points. However the values I'm adding don't make sense to me. My understanding is that the output of VS/GS is in the [-1, 1] space range. However I'm adding 5 to the values and getting a reasonable result as in the attached image. Also the z depth does seem to affect the final size of the particle which is weird to me because the worldviewproj has already been applied.
Does the pipeline do some kind of additional transformation after the GS? Does z affect that? What positional space is the output of the GS in? Clip space (normalized)? Screen space (pixel)?
cbuffer data :register(b0)
{
float4x4 worldViewProj;
float4x4 world;
float4x4 viewProj;
}
struct VS_INPUT
{
float4 position : POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD;
};
struct GS_INPUT
{
float4 position : POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD;
};
struct PS_INPUT
{
float4 position : SV_POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD;
};
Texture2D diffuseMap;
SamplerState textureSampler
{
Filter = MIN_MAG_MIP_LINEAR;
AddressU = Wrap;
AddressV = Wrap;
};
GS_INPUT VS(VS_INPUT input)
{
GS_INPUT output = (GS_INPUT)0;
output.position = mul(worldViewProj, input.position);
output.color = input.color;
output.texcoord = input.texcoord;
return output;
}
[maxvertexcount(4)]
void GS(point GS_INPUT input[1], inout TriangleStream<PS_INPUT> outputStream)
{
PS_INPUT vertices[4];
float s = 5.0;
float2 a = float2(-1, -1) * s;
float2 b = float2(+1, -1) * s;
float2 c = float2(-1, +1) * s;
float2 d = float2(+1, +1) * s;
vertices[0].color = input[0].color;
vertices[1].color = input[0].color;
vertices[2].color = input[0].color;
vertices[3].color = input[0].color;
vertices[0].texcoord = float2(0, 0);
vertices[1].texcoord = float2(0, 1);
vertices[2].texcoord = float2(1, 0);
vertices[3].texcoord = float2(1, 1);
vertices[0].position.zw = input[0].position.zw;
vertices[1].position.zw = input[0].position.zw;
vertices[2].position.zw = input[0].position.zw;
vertices[3].position.zw = input[0].position.zw;
vertices[0].position.xy = input[0].position.xy + a;
vertices[1].position.xy = input[0].position.xy + b;
vertices[2].position.xy = input[0].position.xy + c;
vertices[3].position.xy = input[0].position.xy + d;
outputStream.Append(vertices[0]);
outputStream.Append(vertices[1]);
outputStream.Append(vertices[2]);
outputStream.Append(vertices[3]);
outputStream.RestartStrip();
}
float4 PS(PS_INPUT input) : SV_TARGET
{
return diffuseMap.Sample(textureSampler, input.texcoord) * input.color;
//return input.color;
}
