[vtkusers] why volume rendering with 2d texture mapping much slower than 3d texture mapping?

[Moreland, Kenneth]

I have not looked at the code for these two mappers for some time, but I can
propose a couple of hypotheses.  The 2D texture mapping has to swap out all
the texture data every time you move the camera past the 45 degree viewing
angle to the normal of the planes being rendered.  If you are moving the
camera a lot, then the 2D approach is bound to be slower.  Another
possibility is that (I think) the 2D approach creates multiple texture
objects: one texture for each plane being rendered.  Your graphics hardware
may not be handling these multiple textures well.  It could even be that
only a few are actually loaded on the card at any given time, and that there
is a significant amount of data swapping per frame.

At any rate, all things being equal, the 3D texture mapper gives better
results.  The 2D texture mapper probably would not exist if 3D textures were
supported by OpenGL 1.1 (and thus not supported by all graphics hardware).
So relax, use the 3D texture mapper, and enjoy.

-Ken


On 7/25/08 4:07 AM, "liu" <liuwenqing306 at gmail.com> wrote:

> Hi everyone,
> why volume rendering with 2d texture mapping much slower than 3d texture
> mapping in my computer?My GPU is 8800GT, I got 60fps using 3d-texture
> mapping,and only 7fps using 2d-texture mapping.It's so weird,any one knows?