CODEWITHSUNDEEP
opengl
jalal sadeghi
jalal sadeghi

Reputation: 382

OpenGl Texture unit

’m observing a strange behavior from my application which I hope you can explain to me. You see, I have these two 3D textures that are being sent to the fragment shader and are rendered perfectly OK. But there is a problem, As soon as I even create another texture (it’s a 1D texture), a black screen is being rendered instead of the correct former result.

About this 1D texture, I’m not even sending it to the fragment shader. The minute I call glTexImage1D(…) the black screen shows up. I comment this line and it goes away!!And the two textures are rendered.

I figured there has to be some kind of problem with texture units. Because when I run the application with gDebugger, the texture unit of one of 3D textures is THE SAME as the one assigned to the 1D texture.

I did not assign any texture unit to the 1D texture, I just created it. Apparently texture unit GL_TEXTURE0 is being automatically assigned to the 1D texture. The weird part is that although I use GL_TEXTURE2 and GL_TEXTURE3 for the 3D texture, one of them is being bound to GL_TEXTURE0 as a result of calling glTexImage1D!

Here is a snapshot from the textures list window of gDebugger:

Texture 1 (unit 2 ,bound3d)-enabled Texture 2 (unit 0 ,bound1d) Texture 3 (unit 0 ,bound3d)-Enabled (unit 3,bound3D)-enabled

Why is this happening?

the problem is not why texture 1D is being bound to GL_TEXTURE0, it is why it can affect the state of another already bound texture. the code is like this : .

...
// generating  the first texture_3d
glTexImage(GL_TEXTURE_3D,....);
glBindTexture(GL_TEXTURE_3D,id1);

    //render loop for the first texture_3d
    GLuint glEnum = GL_TEXTURE2;
    vtkgl::ActiveTexture(glEnum);
    glBindTexture(vtkgl::TEXTURE_3D,id1);
    program->setUniform("TEX1",2);

    // generating  the second texture_3d
    glTexImage(GL_TEXTURE_3D,....);
    glBindTexture(GL_TEXTURE_3D,id2);

    //render loop for the first texture_3d
    GLuint glEnum = GL_TEXTURE3;
    vtkgl::ActiveTexture(glEnum);
    glBindTexture(vtkgl::TEXTURE_3D,id2);
    program->setUniform("TEX2",3);

    // generating  texture 1D
    glTexImage(GL_TEXTURE_1D,....);
    glBindTexture(GL_TEXTURE_1D,id3);

    we expect GL_TEXTURE2 and GL_TEXTURE3 to be active but gDebugger indicates that GL_TEXTURE0 and GL_TEXTURE2 are active.

Upvotes: 1

Views: 3715

Answers (2)

fintelia
fintelia

Reputation: 1211

You should not have both 1D and 3D textures bound to the same texture unit at the same time. To avoid this, either unbind the 3D texture: glBindTexture() or switch to a new texture unit: vtkgl::ActiveTexture() before binding the 1D texture.

As the above poster has stated, the call to vtkgl::ActiveTexture() must come before the corresponding call to glBindTexture().

Upvotes: 1

SigTerm
SigTerm

Reputation: 26409

Call glActiveTexture BEFORE glBindTexture

glBindsTexture binds to CURRENT active texture, so in your current code you first you bind id1 to texture 0, then bind it again to texture2, then bind id2 to texture2 (replacing id1), etc.

Upvotes: 4

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