Hello,
I'm trying to implement Nvidias Screen Space Fluid Rendering in Ogre using Direct3D9 as my rendering system. (http://developer.download.nvidia.com/presentations/2010/gdc/Direct3D_Effects.pdf for slides and https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDoQFjAA&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.157.909%26rep%3Drep1%26type%3Dpdf&ei=dlrsUJX6Jq364QSdxIHgAg&usg=AFQjCNEXlV2bFFL0uSrDofS65HAHbtpUHg&sig2=02fSfNNvdlQEO6Pjq2LNQA&bvm=bv.1357316858,d.Yms for paper).
I got my billboard quad particles and using a shader they look like spheres. I save the depth from those spheres in a texture.
At the next step I have to blur the depth.
Now I put this blurred texture on a screen filling quad and let the next shader run on it.
Now I have to create the normals at this point. To get the normals I have to calculate the view-space coordinates from the depth and texture coordinates (see slide 18).
My problem is the mysterious uvToEye-function.
I found some code to recalculate the coordinates here: http://mynameismjp.wordpress.com/2009/03/10/reconstructing-position-from-depth/ but it doesn't work (all I seem to get is (0,0,0) for every point).
This is my code: I skipped the blur-step since I figured there is no need to blur the depth before I cant calculate normals from it.
My vertex shader for depth and making the billboardquads spherical:
struct VertexIn
{
float4 pos : POSITION;
float2 texco : TEXCOORD0;
};
struct VertexOut
{
float4 pos : POSITION;
float2 texco : TEXCOORD0;
float3 eyeSpacePos : TEXCOORD1;
};
struct PixelInput
{
float2 texco : TEXCOORD0;
float3 eyeSpacePos : TEXCOORD1;
};
struct PixelOutput
{
float4 color : COLOR0;
};
VertexOut mainVS( VertexIn input,
uniform float4x4 worldViewProj_m,
uniform float4x4 worldView_m,
uniform float sphereRadius
)
{
VertexOut output = (VertexOut)0;
input.pos.y += sphereRadius; //partikel nicht im Boden versinken lassen
output.pos = mul( worldViewProj_m, input.pos );
output.texco = input.texco;
output.eyeSpacePos = mul(worldView_m, input.pos).xyz;
return output;
}
PixelOutput mainPS(PixelInput input,
uniform float4x4 projMatrix,
uniform float sphereRadius
)
{
PixelOutput output = (PixelOutput)0;
// calculate eye-space sphere normal from texture coordinates
float3 N;
N.xy = input.texco*2.0-1.0;
float r2 = dot(N.xy, N.xy);
if (r2 > 1.0) discard; // kill pixels outside circle
N.z = sqrt(1.0 - r2);
// calculate depth
float4 pixelPos = float4(input.eyeSpacePos + N*sphereRadius, 1.0); //approximation of a sphere
float4 clipSpacePos = mul(projMatrix,pixelPos);
float fragDepth = clipSpacePos.z / clipSpacePos.w;
output.color.r = fragDepth;
return output;
}
And this is my shader for calculating the normals:
struct VertexIn
{
float4 pos : POSITION;
float2 texco : TEXCOORD0;
};
struct VertexOut
{
float4 pos : POSITION;
float2 texco : TEXCOORD0;
};
struct PixelInput
{
float2 texco : TEXCOORD0;
};
struct PixelOutput
{
float4 color : COLOR0;
};
VertexOut mainVS(VertexIn input,
uniform float4x4 worldViewProj_m)
{
VertexOut output = (VertexOut)0;
output.pos = mul( worldViewProj_m, input.pos );
output.texco = input.texco;
return output;
}
float3 uvToEye(float2 texCoord, float depth, float4x4 iP_m){
// Get x/w and y/w from the viewport position
float x = texCoord.x * 2.0 - 1.0;
float y = (1 - texCoord.y) * 2.0 - 1.0;
//float y = texCoord.y * 2.0 - 1.0;
float4 clipPos = float4(x , y, depth, 1.0f);
// Transform by the inverse projection matrix
//float4 viewPos = mul(clipPos, iP_m);
float4 viewPos = mul(iP_m , clipPos);
// Divide by w to get the view-space position
return viewPos.xyz / viewPos.w;
}
PixelOutput mainPS(PixelInput input,
uniform sampler depthTex: register(s0),
uniform float4x4 invProj_m)
{
PixelOutput output = (PixelOutput)0;
// read eye-space depth from texture
float depth = tex2D(depthTex, input.texco).r;
// calculate eye-space position from depth
float texelSize = 0.0001; // correct value?
// calculate differences
float3 ddx1 = uvToEye(input.texco + float2(texelSize, 0), tex2D(depthTex, input.texco + float2(texelSize, 0)).r, invProj_m) - posEye;
float3 ddx2 = posEye - uvToEye(input.texco + float2(-texelSize, 0), tex2D(depthTex, input.texco + float2(-texelSize, 0)).r, invProj_m);
ddx1 = -ddx2 + ddx1;
if (abs(ddx1.z) > abs(ddx2.z)) {
ddx1 = ddx2;
}
float3 ddy1 = uvToEye(input.texco + float2(0, texelSize), tex2D(depthTex, input.texco + float2(0, texelSize)).r, invProj_m) - posEye;
float3 ddy2 = posEye - uvToEye(input.texco + float2(0, -texelSize), tex2D(depthTex, input.texco + float2(0, -texelSize)).r, invProj_m);
ddy1 = -ddy2 + ddy1;
if (abs(ddy2.z) < abs(ddy1.z)) {
ddy1 = ddy2;
}
// calculate normal
float3 n = cross(ddx1, ddy1);
n = normalize(n);
//output.color = float4(posEye, 1.0); // for testing, results in a black screen
output.color = float4(n,1);
return output;
}
I hope someone here can tell me what I'm doing wrong and what is the right way to do it.
Regards,
Kilian
