Question

’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.

Answer 1

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().