rendering a UIImage using openGL - ios

Question

I use the following code to render a UIImage using openGL. the Texture2D class is from Apple, so I assume it's correct. The image does not get displayed. I just get the background color produced by glClearColor. My app is based on GLpaint sample code from Apple, so the setup is correct and I am able to draw lines using openGL just fine.
Is this render code below missing something?
- (void) render:(UIImage *)image
{
[EAGLContext setCurrentContext:context];
glViewport(0, 0, backingWidth, backingHeight);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// texturing will need these
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glEnableClientState(GL_VERTEX_ARRAY);
glEnable(GL_TEXTURE_2D);
glOrthof(0, backingWidth, 0, backingHeight, -1, 1);
glMatrixMode(GL_MODELVIEW);
glClearColor(0.2f, 0.2f, 0.2f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
Texture2D *texture = [[Texture2D alloc] initWithImage:image];
[texture drawInRect: self.frame];
// This application only creates a single color renderbuffer which is already bound at this point.
// This call is redundant, but needed if dealing with multiple renderbuffers.
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER];
}

Answer 1

update: replaced the broken link in the original answer with actual code.
Here is the code that worked for me:
-(void) mergeWithImage:(UIImage*) image
{
if(image==nil)
{
return;
}
glPushMatrix();
glColor4f(256,
256,
256,
1.0);
GLuint stampTexture; // = texture.id;
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glGenTextures(1, &stampTexture);
glBindTexture(GL_TEXTURE_2D, stampTexture);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
GLuint imgwidth = CGImageGetWidth(image.CGImage);
GLuint imgheight = CGImageGetHeight(image.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc( imgheight * imgwidth * 4 );
CGContextRef context2 = CGBitmapContextCreate( imageData, imgwidth, imgheight, 8, 4 * imgwidth, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );
CGContextTranslateCTM (context2, 0, imgheight);
CGContextScaleCTM (context2, 1.0, -1.0);
CGColorSpaceRelease( colorSpace );
CGContextClearRect( context2, CGRectMake( 0, 0, imgwidth, imgheight ) );
CGContextTranslateCTM( context2, 0, imgheight - imgheight );
CGContextDrawImage( context2, CGRectMake( 0, 0, imgwidth, imgheight ), image.CGImage );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imgwidth, imgheight, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
CGContextRelease(context2);
free(imageData);
static const GLfloat texCoords[] = {
0.0, 1.0,
1.0, 1.0,
0.0, 0.0,
1.0, 0.0
};
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
/*
These arrays would need to be changed if the size of the paintview changes. You must make sure that all image imput is 64x64, 256x256, 512x512 or 1024x1024. Here we are using 512, but you can use 1024 as follows:
use the numbers:
{
0.0, height, 0.0,
1024, height, 0.0,
0.0, height-1024, 0.0,
1024, height-1024, 0.0
}
*/
NSLog(#"height of me: %f", self.bounds.size.height);
static const GLfloat vertices[] = {
0.0, 643, 0.0,
1024, 643, 0.0,
0.0, -381, 0.0,
1024, -381, 0.0
};
static const GLfloat normals[] = {
0.0, 0.0, 1024,
0.0, 0.0, 1024,
0.0, 0.0, 1024,
0.0, 0.0, 1024
};
glBindTexture(GL_TEXTURE_2D, stampTexture);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glNormalPointer(GL_FLOAT, 0, normals);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glPopMatrix();
glDeleteTextures( 1, &stampTexture );
// Display the buffer
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
}
-(void) addImageToView{
UIImage* imageToAdd= [UIImage imageNamed:#"IMAGE_TO_ADD_TO_GL_VIEW.png"];
// all images added to the paining view MUST be 512x512.
// You can also add smaller images (even transformed ones) using this method - just add it to a UIView and then get it's graphics context
UIView* imageView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 512, 512)];
UIImageView* subView = [[UIImageView alloc] initWithImage:imageToAdd];
[imageView addSubview:subView];
UIImage* blendedImage =nil;
UIGraphicsBeginImageContext(imageView.frame.size);
[imageView.layer renderInContext:UIGraphicsGetCurrentContext()];
blendedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self mergeWithImage: blendedImage ];