Hi, everyone. I'd like to know more about the following. Let's say I glReadPixels in GL_DEPTH_COMPONENT format with GL_UNSIGNED_SHORT type. I then calculate a float beetween 0 and 1 using glReadPixels man component conversion table. Now, is the coordinate I get a good coordinate in D3D clip space (in shader) (more precisely float4(x, y, depth, 1) in (unnormalized)CS) ? Need I GL unproject and then D3D project (which seems overkill to me) ? (This may be a wrong topic for this forum but I didn't see elsewhere to post) Thanks for helping [Edited by - yazgoo on May 13, 2009 8:24:02 AM]

Quote:Personally, I would avoid using glReadPixels.

I think I didn't explain well enough :
I use glReadPixel to recover the ZBuffer but then i use my depth image in a
D3D program, more precisely in a shader.

A graphic is more appropriate :

Opengl side :   [ OPENGL scene ]----glReadPixels---->[ depth buffer Image]D3D side :   [depth buffer image]--pixelValue-->[ vertex shader ]-->float4(pixelValue,x,y,1)

Quote:Why are you interested in clip space? clip space is just projection * modelview * vertex.

Correct me if I'm wrong, but clip Zbuffer as given by glReadPixel is in OpenGL clip space.
Vertex shader projection is in (D3D) clip space. Then I was thinking I could avoid any projection/unprojection directly giving coordinates in clip space.

So my questions are, more precisely :
- Are OGL(as returned by glReadBuffer and scaled as I explained)/D3D clipping
space coordinates the same ?
- If it isn't is there a simple transformation which would avoid gluUnproject and then mul by WorldViewProj ?

[Edited by - yazgoo on May 13, 2009 10:57:23 AM]

Thank's V-man, but it does not seem to work.
Maybe I'm not declaring clip space coordinates right, this is the way I do
this in my shader :

out.position.z = depth; // between 0 and 1out.position.x = xCoordinate; // between -1 and 1out.position.y = yCoordinate; // between -1 and 1out.position.w = 1;

to calculate the depth I use something like the following
(with a depth texture filled with two bytes zbuffer data) :

depth = (255 * zbuffer.r * 256 + 255 * zbuffer.g) / (pow(2,16)-1);

[Edited by - yazgoo on May 18, 2009 10:51:14 AM]

Turns out I've done a little maths to find if D3D and OpenGl clip spaces
are homogeneous.
Here should be the transformation needed
(on the basis I have openGL clip space coordinates) :

multiply by w; OpenglProjectionInverse; DirectXProjection

Those matrices are :

Pogl: matrix( [n/r,0,0,0],  [0,n/t,0,0],  [0,0,-(n+f)/(f-n),-2*f*n/(f-n)],  [0,0,-1,0]);Pd3d : matrix([n/r,0,0,0],  [0,n/t,0,0],  [0,0,f/(f-n),1],  [0,0,-f*n/(f-n),0]);

and Pd3d * rightHandToLeftHand * Pogl^(-1) is :

matrix( [-1,0,0,0], [0,1,0,0], [0,0,-(f-n)/(2*f*n),-(-n-f)/(2*f*n)-f/(f-n)], [0,0,0,(f*n)/(f-n)])

[edit]I've corrected the matrix and added a left to right hand matrix which is Identity with (0,0) == -1[/edit]

[Edited by - yazgoo on May 19, 2009 10:45:02 AM]