GlGenTextures keeps returing 0's

c++ c opengl

12,484

Solution 1

Try calling glGetError. It should tell you in more detail what went wrong. In general, if an OpenGL function fails, the first thing you do should be to ask OpenGL why it failed. It knows, because it just tried to execute the function.

It's much harder for us to guess at what might have gone wrong.

Solution 2

You probably are calling glGenTextures before creating the OpenGL context, and that will generate a GL error. Don't try to create textures before you've initialized OpenGL.

Solution 3

I had this problem, and glGetError() was returning 0.

In my case it was caused by calling glGenTextures(...) on a different thread to the one the GL context was created on (because I was loading the textures asynchronously). Calling it from the main thread after the async load made glGenTextures(...) start working again.

12,484

Author by

jmasterx

Updated on June 09, 2022

Comments

jmasterx almost 2 years

I'm trying to generate textures like so:

#define checkImageWidth 64
#define checkImageHeight 64
static GLubyte checkImage[checkImageHeight][checkImageWidth][4];
static GLubyte otherImage[checkImageHeight][checkImageWidth][4];

static GLuint texName[2];

void makeCheckImages(void)
{
    int i, j, c;

    for (i = 0; i < checkImageHeight; i++) {
        for (j = 0; j < checkImageWidth; j++) {
            c = ((((i&0x8)==0)^((j&0x8))==0))*255;
            checkImage[i][j][0] = (GLubyte) c;
            checkImage[i][j][1] = (GLubyte) c;
            checkImage[i][j][2] = (GLubyte) c;
            checkImage[i][j][3] = (GLubyte) 255;
            c = ((((i&0x10)==0)^((j&0x10))==0))*255;
            otherImage[i][j][0] = (GLubyte) c;
            otherImage[i][j][1] = (GLubyte) 0;
            otherImage[i][j][2] = (GLubyte) 0;
            otherImage[i][j][3] = (GLubyte) 255;
        }
    }
}
void init(void)
{    
    glClearColor (1.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
    glEnable(GL_DEPTH_TEST);

    makeCheckImages();
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    glGenTextures(2, texName);
    glBindTexture(GL_TEXTURE_2D, texName[0]);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
        GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
        GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth,
        checkImageHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE,
        checkImage);

    glBindTexture(GL_TEXTURE_2D, texName[1]);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
        GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
        GL_NEAREST);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);   
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth, 
        checkImageHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, 
        otherImage);
    glEnable(GL_TEXTURE_2D);

    engineGL.current.tex = texName[1];
}

But when I check the values of texName[0] and [1] they are both 0, I do not understand why, what am I doing wrong. Thanks.

josesuero almost 14 years

Is that the only function that fails?
jmasterx almost 14 years

No, other things are failing too, I'm calling init() after setting up my context...
Jerry Coffin almost 14 years

have you verified that you're succeeding in setting up your context?
josesuero almost 14 years

If other functions are failing too, then write the shortest code snippet you can in which a function fails, so you can narrow down where the error is introduced.

josesuero almost 14 years

Use gluErrorString() to find out. :) opengl.org/wiki/…
josesuero almost 14 years

The (documentation)[opengl.org/sdk/docs/man/xhtml/glGenTextures.‌xml] mentiones that "GL_INVALID_OPERATION is generated if glGenTextures is executed between the execution of glBegin and the corresponding execution of glEnd.". Does that help you?
jmasterx almost 14 years

Yea I had seen this but I don't do any sort of rendering before calling init() so im confused.
jmasterx almost 14 years

Yes, that was 1 of my issues, I was also calling wglmakecurrent in my render loop which was causing trouble