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POiOS OpenGL ES 2.0: Offscreen render and save the result to an UIImage
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  1. POiOS OpenGL ES 2.0: Offscreen render and save the result to an UIImage
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    copied!<p>I'm using OpenGL ES to render some special effects, I don't want to show this to user, I just want to save the result as an UIImage, can anybody please help me?</p> <p>this is the code I'm using, I can get an image which contains the red clear color I use, but no geometry drawing shown.</p> <pre><code>#import "RendererGL.h" #import &lt;GLKit/GLKit.h&gt; #import &lt;UIKit/UIKit.h&gt; #import &lt;OpenGLES/EAGL.h&gt; #import &lt;OpenGLES/EAGLDrawable.h&gt; #import &lt;OpenGLES/ES2/glext.h&gt; #import &lt;QuartzCore/QuartzCore.h&gt; static NSInteger WIDTH_IN_PIXEL = 400; static NSInteger HEIGHT_IN_PIXEL = 300; typedef struct { GLKVector3 positionCoords; } SceneVertex; static const SceneVertex vertices[] = { {{-0.5f, -0.5f, 0.0}}, // lower left corner {{ 0.5f, -0.5f, 0.0}}, // lower right corner {{-0.5f, 0.5f, 0.0}} // upper left corner }; @implementation RendererGL { EAGLContext* _myContext; GLuint _framebuffer; GLuint _colorRenderbuffer; GLuint _depthRenderbuffer; GLuint _vertexBufferID; GLKBaseEffect *_baseEffect; } - (id) init { self = [super init]; if (self) { _myContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]; [EAGLContext setCurrentContext:_myContext]; [self setupOffscreenBuffer]; [self setUpEffect]; [self renderImage]; [self saveImage]; //this do works, since I get an image, but the image only contains the red color I used to clear } return self; } -(void)setUpEffect { _baseEffect = [[GLKBaseEffect alloc] init]; _baseEffect.useConstantColor = GL_TRUE; _baseEffect.constantColor = GLKVector4Make(0.0f, 0.0f, 1.0f, 1.0f); } //this code is from apples document -(void)setupOffscreenBuffer { glGenFramebuffers(1, &amp;_framebuffer); glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer); glGenRenderbuffers(1, &amp;_colorRenderbuffer); glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderbuffer); glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA4, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL); glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _colorRenderbuffer); glGenRenderbuffers(1, &amp;_depthRenderbuffer); glBindRenderbuffer(GL_RENDERBUFFER, _depthRenderbuffer); glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL); glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, _depthRenderbuffer); GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ; if(status != GL_FRAMEBUFFER_COMPLETE) { NSLog(@"failed to make complete framebuffer object %x", status); } } - (void) renderImage { GLenum error = GL_NO_ERROR; glClearColor(1, 0, 0, 1); //red clear color, this can be seen glClear(GL_COLOR_BUFFER_BIT); glEnable(GL_DEPTH_TEST); [_baseEffect prepareToDraw]; glGenBuffers(1, &amp;_vertexBufferID); glBindBuffer(GL_ARRAY_BUFFER, _vertexBufferID); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); error = glGetError(); if (error != GL_NO_ERROR) { NSLog(@"error happend, error is %d, line %d",error,__LINE__); } glEnableVertexAttribArray(GLKVertexAttribPosition); glVertexAttribPointer(GLKVertexAttribPosition,3,GL_FLOAT, GL_FALSE, sizeof(SceneVertex), NULL); glDrawArrays(GL_TRIANGLES,0,3); error = glGetError(); if (error != GL_NO_ERROR) { NSLog(@"error happend, error is %d, line %d",error,__LINE__); } glFinish(); error = glGetError(); if (error != GL_NO_ERROR) { NSLog(@"error happend, error is %d, line %d",error,__LINE__); } } -(void)saveImage { GLenum error = GL_NO_ERROR; NSInteger x = 0, y = 0; NSInteger dataLength = WIDTH_IN_PIXEL * HEIGHT_IN_PIXEL * 4; GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte)); glPixelStorei(GL_PACK_ALIGNMENT, 4); glReadPixels(x, y, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL, GL_RGBA, GL_UNSIGNED_BYTE, data); NSData *pixelsRead = [NSData dataWithBytes:data length:dataLength]; error = glGetError(); if (error != GL_NO_ERROR) { NSLog(@"error happend, error is %d, line %d",error,__LINE__); } CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL); CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB(); CGImageRef iref = CGImageCreate(WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL, 8, 32, WIDTH_IN_PIXEL * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast, ref, NULL, true, kCGRenderingIntentDefault); UIGraphicsBeginImageContext(CGSizeMake(WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL)); CGContextRef cgcontext = UIGraphicsGetCurrentContext(); CGContextSetBlendMode(cgcontext, kCGBlendModeCopy); CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL), iref); UIImage *image = UIGraphicsGetImageFromCurrentImageContext(); NSData *d = UIImageJPEGRepresentation(image, 1); NSString *documentDirPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0]; static NSInteger imageNO = 1; imageNO++; NSString *savingPath = [documentDirPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%d.jpg",imageNO]]; BOOL succ = [d writeToFile:savingPath atomically:NO]; //is succeeded UIGraphicsEndImageContext(); free(data); CFRelease(ref); CFRelease(colorspace); CGImageRelease(iref); } @end </code></pre>
 

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