Can't load image into OpenGLES 2.0 Texture

Question

I'm trying to load a screenshot into an OpenGLES Texture, but when i display it, it is just black.

Here is how I get the screenshot:

UIGraphicsBeginImageContext(self.bounds.size);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

and here is how I'm trying to load the image into the Texture:

GLuint setupTextureFromImage(UIImage* image) {
    CGImageRef spriteImage = image.CGImage;
    if (!spriteImage) {
        NSLog(@"Failed to load image");
        exit(1);
    }

    size_t width = CGImageGetWidth(spriteImage);
    size_t height = CGImageGetHeight(spriteImage);

    GLubyte * spriteData = (GLubyte *) calloc(width*height*4, sizeof(GLubyte));

    CGContextRef spriteContext = CGBitmapContextCreate(spriteData, width, height, 8, width*4, CGImageGetColorSpace(spriteImage), kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Host);

    CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), spriteImage);

    CGContextRelease(spriteContext);

    GLuint texName;
    glGenTextures(1, &texName);
    glBindTexture(GL_TEXTURE_2D, texName);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (int) width, (int) height, 0, GL_RGBA, GL_UNSIGNED_BYTE, spriteData);

    free(spriteData);
    return texName;
}

if I load an image from the resources with [UIImage imageNamed: @"FileName.png"] it works and if I'm setting the screenshot as the background color it also works, so both parts work separately

How big is it? I've had textures quietly not load in the past because they were over a certain size. That was on Android, but from what I remember it's more about the GPU than the platform... Someone seems to have [a handy table for iOS max texture sizes here](http://www.uchidacoonga.com/2012/04/quick-tip-max-texture-size/). — Matt Gibson, Aug 13 '14 at 22:31
... though at runtime, on a specific device, you should use `glGet` with `GL_MAX_TEXTURE_SIZE` to figure out if your images are too large and either split it up or shrink it if necessary. — Tommy, Aug 13 '14 at 22:43
Okay, so you should be fine [up to 4096x4096](http://stackoverflow.com/questions/25226653/glerror-0x0501-when-loading-a-large-texture-with-opengl-es-on-the-iphone4), so it's probably not that if you're just doing it with a screenshot. Might be worth just checking width and height to see if they're what you expect, though. — Matt Gibson, Aug 13 '14 at 23:03
Is there data in `spriteData` after the `CGContextDrawImage` call? Since you allocated it zero filled, it should be easy to see in a debugger if the image data was successfully written to it. — Reto Koradi, Aug 14 '14 at 02:27

Can't load image into OpenGLES 2.0 Texture

0 Answers0