Hi there! I'm trying to reconstruct 3d pixel position from depth. I read many threads and many papers since many weeks and I want to make a little demo. I believe you can help me, I really appreciate your help. I have implemented 2 situation: - Comparation in world space: deferred pass, I store world pixel position and in light pass I compare with light position in world space. 1 texture of my G-Buffer for that, xyz. - Comparation in view-space: the same as below but in view-space, I need to do mModelView * lightPosition for to compare. And now I try to implement Crytek or policarpo approach that you comment in many threads and in MJP's blog. At first I save depth in W or A in my color buffer: float pixelDepth = (viewPosition.z - zNear) / (zFar - zNear); Later in my application I put in multiTexCoord1 far plane like your code, extracting it from projection matrix like MJP say in a comment: top-left: -500, 500, 1000 top-right: 500, 500, 1000 bottom-left: -500, -500, 1000 bottom-right: 500, -500, 1000 In my light pass I try to restore 3D pixel position: // Restore depth float pixelDepthView = ((zFar - zNear) * viewPosition.w) + zNear; // This is definitely wrong vec3 pixelPosition = eyePosition + (farPlaneCoord.xyz * viewPosition.w); I tried other things like trace a ray from pixel, apply modelView matrix (only rotation)... I need help at this point. Thanks for your time. [Edited by - Prompt on July 24, 2009 11:13:31 AM]

Hi
Crytek describes a technique in this paper : http://developer.amd.com/assets/D3DTutorial_Crytek.pdf

In Vertex Shader you create a ray by using coordinate and inverse viewproj
matrice. Something like:
float3 start = float3(input.uv, 0.f) * InvViewProj;
ouput.ray = start - ViewPos;
ouput.ray.Normalize();

or

float3 start = float3(input.uv, 0.f) * InvViewProj;
float3 end = float3(input.uv, 1.f) * InvViewProj;
ouput.ray = end - start;
ouput.ray.Normalize();

In pixel shader you just have to do :
float depth = tex2D(...); //the depth need to be the distance between the camera and the objet in linear (not like in the Depth buffer)
float3 pos = input.ray * depth;

I never did it but I think it's something like that

good luck

Yes it's so simple, but I have something wrong in my code.

How can I test my farPlane?

I test world position rendering a red line like this:
if ( pixelPosition.x > 0.0 && pixelPosition.x < 10.0 )
gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
else
discard;

I need to be sure that my farPlane coords are ok, but how?

I use this method:
glMultiTexCoord2i(GL_TEXTURE0, 0, 1); glMultiTexCoord3f(GL_TEXTURE1, _texCoord[0].x, _texCoord[0].y, _texCoord[0].z); glVertex2i(0, 0);
glMultiTexCoord2i(GL_TEXTURE0, 1, 1); glMultiTexCoord3f(GL_TEXTURE1, _texCoord[1].x, _texCoord[1].y, _texCoord[1].z); glVertex2i(1, 0);
glMultiTexCoord2i(GL_TEXTURE0, 1, 0); glMultiTexCoord3f(GL_TEXTURE1, _texCoord[2].x, _texCoord[2].y, _texCoord[2].z); glVertex2i(1, 1);
glMultiTexCoord2i(GL_TEXTURE0, 0, 0); glMultiTexCoord3f(GL_TEXTURE1, _texCoord[3].x, _texCoord[3].y, _texCoord[3].z); glVertex2i(0, 1);


vertex are in correct OpenGL order:
0, 0
1, 0
1, 1
0, 1

texCoords are in other order for to be Z looking camera:
0, 1
1, 1
1, 0
0, 0

And far clip plane:
+[0] { x=-557.75 y= 557.75 z=1000.0 }
+[1] { x= 557.75 y= 557.75 z=1000.0 }
+[2] { x= 557.75 y=-557.75 z=1000.0 }
+[3] { x=-557.75 y=-557.75 z=1000.0 }

I think this it's ok too, I'm wrong?

Quote:Original post by kociolek
This is my code for FarPlane point calculation

float hFovTan = (float)Math.Tan(Camera.FOV*0.5f);
float H = hFovTan*Camera.Clip.Y;//Far (eg. 10000)
float W = H*Camera.Aspect;//>1

FarPoint[0] = Vector3.Transform(new Vector3(-W, H, -Camera.Clip.Y), Camera.RotationMatrix);
FarPoint[1] =Vector3.Transform( new Vector3(W, H,-Camera.Clip.Y), Camera.RotationMatrix);
FarPoint[2] =Vector3.Transform( new Vector3(W, -H,-Camera.Clip.Y), Camera.RotationMatrix);
FarPoint[3] = Vector3.Transform(new Vector3(-W, -H, -Camera.Clip.Y), Camera.RotationMatrix);

in shader:
Decoding:
CameraPos.xyz + tex2D(DepthTexture, UV.xy).r*InterpolatedCorners.xyz;

Encoding:
(vertex shader)
OUT.Depth = mul(float4(IN.Position.xyz),1), WorldViewProj).w*Clip.w;//w = 1/far
W value is more "stable" than Z (in my case)

Yes this is correct :)

Some documentation about my implementation based on your code:
- In application:
float eyeFOV = m_pActiveCamera->getFov( );
float aspectRatio = m_pActiveCamera->getAspectRatio( );

float radFOV = eyeFOV * Math::PI / 180.0f;
float hFovTan = tan(radFOV * 0.5f); // Note: need radians here!
float H = hFovTan * zFar; // Far (eg. 10000)
float W = H * aspectRatio; // >1

Matrix4 modelViewInvRotation = viewMatrix.inverse( ); // ModelView Inverse is needed
modelViewInvRotation.translate( 0.0f, 0.0f, 0.0f ); // Only rotation
texCoord[0] = Vector3(-W, H, -zFar) * modelViewInvRotation;
texCoord[1] = Vector3( W, H, -zFar) * modelViewInvRotation;
texCoord[2] = Vector3( W, -H, -zFar) * modelViewInvRotation;
texCoord[3] = Vector3(-W, -H, -zFar) * modelViewInvRotation;



I have this camera config:
fovX = 45
zFar = 1e+006
zNear = 15

And testing some thing i use in my color buffer W, depth / zFar, before I used:
float pixelDepth = (viewPosition.z - zNear) / (zFar - zNear);

But for me this is the correct way:
float pixelDepth = viewPosition.z / zFar

So in deferred pass:
- vertex shader:
positionView = gl_ModelViewMatrix * positionWorld;

- fragment shader:
gl_FragData[1] = vec4(normal.xyz, viewPosition.z / zFar);

In light pass:
- vertex shader:
farPlaneCoord = gl_MultiTexCoord1;

- fragment shader:
vec3 lightPosition = lightPos.xyz;
vec3 pixelPosition = eyePosition.xyz - viewPosition.w * farPlaneCoord.xyz;

This is so rare thing... I need to deduct eyePosition, I need to debug:
Matrix4 modelViewInvRotation = viewMatrix.inverse( );
modelViewInvRotation.translate( 0.0f, 0.0f, 0.0f );

Because is so strange, maybe is for to use Inverse of the modelview matrix.

Thanks for all kociolek and Squallc