Question

I have been at this for quite some time now, reading tutorials and so on, and I can’t work out what the heck is wrong with this, is anyone else able to help me understand what is going wrong?

// Sets up an array of values to use as the sprite vertices.
const GLfloat spriteVertices[] = {
    20.0f, 50.5f,
    305.0f, 50.0f,
    10.5f,  200.5f,
    300.5f,  300.5f,
};

// Sets up an array of values for the texture coordinates.
const GLshort spriteTexcoords[] = {
    0, 0,
    100, 0,
    0, 100,
    100, 100,
};

-(void)setupView:(GLView*)view {
    glMatrixMode(GL_PROJECTION); 
    CGRect rect = view.bounds; 

    glOrthof(0, rect.size.width, rect.size.height, 0, -1, 1);
    glViewport(0, 0, rect.size.width, rect.size.height);  
    glMatrixMode(GL_MODELVIEW);
    glDepthMask(GL_FALSE);
    glLoadIdentity();

    CGImageRef spriteImage = [UIImage imageNamed:@"rss_icon.png"].CGImage;
    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
    );

    CGContextDrawImage(
      spriteContext, 
      CGRectMake( 0.0, 0.0, (CGFloat)width, (CGFloat)height), 
      spriteImage
    );

    CGContextRelease(spriteContext);

    glGenTextures(1, &texture[0]);
    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); 
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); 
    glTexImage2D(
      GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, 
      GL_RGBA, GL_UNSIGNED_BYTE, spriteData
    );
    free(spriteData);

    glEnable(GL_TEXTURE_2D);
    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_BLEND);
}

Draw code:

- (void)drawView:(UIView *)theView {
    glLoadIdentity();
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glEnable(GL_TEXTURE_2D);
    glEnable(GL_BLEND);

    glVertexPointer(2, GL_FLOAT, 0, spriteVertices);
    glEnableClientState(GL_VERTEX_ARRAY);
    glTexCoordPointer(2, GL_SHORT, 0, spriteTexcoords);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

Answer 1

The obvious problem might be that your texture has dimensions that are not a power of two. There’s a hardware restriction on iphone that requires them to be that way

From Apple’s iPhone OpenGL ESProgramming Guide:

The following are known limitations as
of iPhone OS 3.0: The PowerVR SGX does
not support non–power of two cube
mapped or mipmapped textures