CODEWITHSUNDEEP
cudatextures
TonyLic
TonyLic

Reputation: 667

When using 3D Texture In CUDA, why we don't need to set Texture coordinate?

In OpenGL, after creating a 3D Texture, we always need to draw a proxy geometry such as GL_QUADS to contain the 3D Texture and set the texture coordinate in this function: glTexCoord3f.

However, when I use 3D texture in CUDA, I've never found a function like glTexCoord3f to point out the texture coordinate. Actually, we just use the CUDA array and then bind the array to the texture. After this, we can use texture fetch function tex3D to get the value.

Therefore, I'm very confused about that how can the tex3D function run correctly even though we've never set the texture coordinate before????

Thanks for answering.

Upvotes: 1

Views: 780

Answers (1)

harrism
harrism

Reputation: 27829

The texture coordinates are the input arguments to the tex3D() fetch function.

In more detail, in OpenGL, when you call glTexCoord3f() it specifies the texture coordinates at the next issued vertex. The texture coordinates at each pixel of the rendered polygon are interpolated from the texture coordinates specified at the vertices of the polygon (typically triangles).

In CUDA, there is no concept of polygons, or interpolation of coordinates. Instead, each thread is responsible for computing (or loading) its texture coordinates and specifying them explicitly for each fetch. This is where tex3D() comes in.

Note that if you use GLSL pixel shaders to shade your polygons in OpenGL, you actually do something very similar to CUDA -- you explicitly call a texture fetch function, passing it coordinates. These coordinates can be computed arbitrarily. The difference is that you have the option of using input coordinates that are interpolated at each pixel. (And you can think of each pixel as a thread!)

Upvotes: 2

Related Questions