the main problem iam facing is that i have a 3D blended volume using 3D texture & i want to cut in to it with a irregular shape (it is acutally a kind of 3d eraser)
thx for help
You could just computationally clip your volume slices to the boundary of the irregular shape.
An approach that used multipass and stencil operations would also work but it would be expensive requiring some per slice multipass approach.
Another way would be to directly write to the 3D textures alpha channel to erase information you do not wish to draw, but still retain the fragment color should you want to undo that operation.
It really depends on the tradeoffs you need to make for your application.
[This message has been edited by dorbie (edited 09-10-2002).]