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PODrawing into OpenGL ES framebuffer and getting UIImage from it on iPhone
 

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    <p>I'm trying to do offscreen rendering of some primitives in OpenGL ES on iOS. The code is as follows:</p> <pre><code>// context and neccesary buffers @interface RendererGL { EAGLContext* myContext; GLuint framebuffer; GLuint colorRenderbuffer; GLuint depthRenderbuffer; } </code></pre> <p>.m file:</p> <pre><code>- (id) init { self = [super init]; if (self) { // initializing context myContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]; [EAGLContext setCurrentContext:myContext]; [self setupOpenGL]; // creating buffers } return self; } -(void) setupOpenGL { int width = 256; int height = 256; // generating buffers and binding them as Apple,s tutorial says glGenFramebuffersOES(1, &amp;framebuffer); glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer); glGenRenderbuffersOES(1, &amp;colorRenderbuffer); glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer); glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, width, height); glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorRenderbuffer); glGenRenderbuffersOES(1, &amp;depthRenderbuffer); glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer); glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, width, height); glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer); GLenum status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) ; if(status != GL_FRAMEBUFFER_COMPLETE_OES) { NSLog(@"failed to make complete framebuffer object %x", status); } } - (UIImage *) renderImage { int width = 256; int height = 256; [EAGLContext setCurrentContext:myContext]; glEnable(GL_DEPTH_TEST); // clear color - cyan glClearColor(0.0f, 1.0f, 1.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // trying to draw some primitive - red line float line[] = {-0.5f, -0.5f, 0.5f, 0.5f}; glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer); //should I do this? glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(2, GL_FLOAT, 0, line); glColor4f(1.0, 0.0, 0.0, 1.0); glLineWidth(10); glDrawArrays(GL_LINES, 0, 2); // draw line with two points [myContext presentRenderbuffer:GL_RENDERBUFFER_OES]; // and this? // then I grab image from _frameBuffer and return it as UIImage - this part is working NSInteger x = 0, y = 0; NSInteger dataLength = width * height * 4; GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte)); glPixelStorei(GL_PACK_ALIGNMENT, 4); glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data); CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL); CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB(); CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast, ref, NULL, true, kCGRenderingIntentDefault); UIGraphicsBeginImageContext(CGSizeMake(width, height)); CGContextRef cgcontext = UIGraphicsGetCurrentContext(); CGContextSetBlendMode(cgcontext, kCGBlendModeCopy); CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, width, height), iref); UIImage *image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); free(data); CFRelease(ref); CFRelease(colorspace); CGImageRelease(iref); return image; } </code></pre> <p>the problem is that -renderImage returning completely cyan image, without red line. What can it be? Did I missed some actions before drawing line?</p>
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    1. CODoes changing the flags on `CGImageCreate()` to `kCGBitmapByteOrderDefault | kCGImageAlphaLast` help? I forget all of the colorspace byte orderings, but that's what I have in my `glReadPixels()` -> UIImage routine here.
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    2. COnope(( this is not the problem
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