How can I dump OpenGL RenderBuffer to PNG or JPG image? - iphone

Question

I'm working on a project which uses OpenGL framebuffer/renderbuffer to draw freehand lines. This App uses OpenGL ES 1.x and I can't figure out how to dump current screen to PNG or JPG image.
Thanks for reading this question.
From OpenGL Newbie.
Codes used to create frame buffer and render buffer.
// Generate IDs for a framebuffer object and a color renderbuffer
glGenFramebuffersOES(1, &viewFramebuffer);
glGenRenderbuffersOES(1, &viewRenderbuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
// This call associates the storage for the current render buffer with the EAGLDrawable (our CAEAGLLayer)
// allowing us to draw into a buffer that will later be rendered to screen wherever the layer is (which corresponds with our view).
[context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(id<EAGLDrawable>)self.layer];
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, viewRenderbuffer);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
// For this sample, we also need a depth buffer, so we'll create and attach one via another renderbuffer.
glGenRenderbuffersOES(1, &depthRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, backingWidth, backingHeight);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);

Answer 1

-(UIImage *)dumpImage
{
GLubyte *buffer = (GLubyte *) malloc(backingWidth * backingHeight * 4);
GLubyte *buffer2 = (GLubyte *) malloc(backingWidth * backingHeight * 4);
GLvoid *pixel_data = nil;
glReadPixels(0, 0, backingWidth, backingHeight, GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid *)buffer);
/* make upside down */
for (int y=0; y<backingHeight; y++) {
for (int x=0; x<backingWidth*4; x++) {
buffer2[y * 4 * backingWidth + x] = buffer[(backingHeight - y - 1) * backingWidth * 4 + x];
}
}
// make data provider from buffer
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, backingWidth * backingHeight * 4, freeImageData);
// set up for CGImage creation
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * backingWidth;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
// Use this to retain alpha
//CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGImageRef imageRef = CGImageCreate(backingWidth, backingHeight, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// make UIImage from CGImage
UIImage *newUIImage = [UIImage imageWithCGImage:imageRef];
return newUIImage;
}
freeImageData() frees data later.
void freeImageData(void *info, const void *data, size_t size)
{
//printf("freeImageData called");
free((void*)data);
}