What are the usual troubleshooting steps for OpenG

Question

After making a few changes in my application, my textures are no longer showing. So far I've checked the following:

• The camera direction hasn't changed.
• I can see the vectors (when colored instead of textured).

Any usual suspects?

Answer 1

One common problem I run into from time to time is

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);

but I forgot to supply mipmaps. Quickfix:

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

Answer 2

Took me some while to figure this out...

glMatrixMode(GL_TEXTURE);
glLoadIdentity();
glDisable(GL_TEXTURE_GEN_S);
glDisable(GL_TEXTURE_GEN_T);
glDisable(GL_TEXTURE_GEN_R);
glDisable(GL_TEXTURE_GEN_Q);

Also make sure to unbind your stuff:

glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glBindVertexArray(0);

If you use a third party engine, which is optimized, it probably has a "direct state access" layer for OpenGL (to not use the slow OpenGL query functions). If so, don't call OpenGL directly, but use the engine wrappers. Otherwise your code doesn't play nice with the rest of the engine code.

Answer 3

Does a glColor3ub(255,255,255) before rendering your textured object help? I think the default OpenGL state multiplies the current glColor by the incoming texel; a stray glColor3ub(0,0,0) will make all your textures look black.

Answer 4

A few more things to check:

• glColorMaterial(...); To make sure colors aren't overwriting the texture
• glEnable/glDisable(GL_LIGHTING); Sometimes lighting can wash out the texture
• glDisable(GL_BLEND); Make sure that you're not blending the texture out
• Make sure the texture coordinates are set properly.

Answer 5

You may want to check the following:

• glEnable(GL_TEXTURE_2D); presence

• glBindTexture(GL_TEXTURE_2D, texture[i]); and glBindTexture(GL_TEXTURE_2D, 0); when you don't need texture anymore

Answer 6

I assume you had the must have operations implemented like glEnable(GL_TEXTURE_2D) and the texture binding since your textures worked fine before and then suddenly they just won't show.

If you are doing Object Oriented code you might want to have the texture generation happen when the thread that is actually doing the draw is instanced, in other words: avoid doing it in constructors or a call coming from a constructor, this might instance your texture object before the window or the app that is going to use it is on.

What I usually do is that I create a manual Init function of the texture creation that is called in the Init function of the App. Therefore I guarantee that the App exist when the binding occurs.

More info here: http://www.opengl.org/wiki/Common_Mistakes#The_Object_Oriented_Language_Problem