IOS螢幕截圖—Opengl截屏

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上篇blog介紹了如何進行普通：IOS螢幕---普通

前面已經說過，使用普通方式截屏，不能能夠截取Opengl渲染的View。就像我們遠程登入了另一台windows電腦時候，能看到對方的案頭等，但對方的視頻我們並不能看到。

對於此類view，我們需要將opengl渲染的view，通過glReadPixels將其所有的像素讀取到數組中，然後通過這些像素資料建立UIImage，詳細代碼如下。

在我們opengl view，實現下面方法

//In Your GL View
//convert opengl data to UIImage-(UIImage *) glToUIImage {    CGSize viewSize=self.frame.size;    NSInteger myDataLength = viewSize.width * viewSize.height * 4;        // allocate array and read pixels into it.    GLubyte *buffer = (GLubyte *) malloc(myDataLength);    glReadPixels(0, 0, viewSize.width, viewSize.height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);        // gl renders "upside down" so swap top to bottom into new array.    // there's gotta be a better way, but this works.    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);    for(int y = 0; y < viewSize.height; y++)    {        for(int x = 0; x < viewSize.width* 4; x++)        {            buffer2[(int)((viewSize.height-1 - y) * viewSize.width * 4 + x)] = buffer[(int)(y * 4 * viewSize.width + x)];        }    }        // make data provider with data.    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);        // prep the ingredients    int bitsPerComponent = 8;    int bitsPerPixel = 32;    int bytesPerRow = 4 * viewSize.width;    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;        // make the cgimage    CGImageRef imageRef = CGImageCreate(viewSize.width , viewSize.height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);        // then make the uiimage from that    UIImage *myImage = [UIImage imageWithCGImage:imageRef];    return myImage;}

另外，我在實現這段代碼時候，一下代碼得到的buffer依然為空白。

glReadPixels(0, 0, viewSize.width, viewSize.height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

google上解釋說，這是ios6的問題。需要在CAEAGLLayer初始化時候設定一下屬性kEAGLDrawablePropertyRetainedBacking 為YES。

如下

CAEAGLLayer *eaglLayer = (CAEAGLLayer *) self.layer;eaglLayer.drawableProperties = @{    kEAGLDrawablePropertyRetainedBacking: [NSNumber numberWithBool:YES],    kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8};

ref:

Download an Image and Save it as PNG or JPEG in iPhone SDK ‹ ObjectGraph Blog

iphone - Why do I get 'No -renderInContext: method found' warning? - Stack Overflow

iphone - Programmatically take a screenshot combining OpenGL and UIKit elements - Stack Overflow

iPhone – saving OpenGL ES content to the Photo Album | BIT-101

opengl es - Why is glReadPixels() failing in this code in iOS 6.0? - Stack Overflow