iOS 屏幕截图失败，使用 OpenGL

Question

这是我的代码:

@implementation UIView (LCExtension)

- (UIImage *)screenshotWithRect:(CGRect)rect {

    UIGraphicsBeginImageContext(self.bounds.size);
    [self.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    image = [UIImage imageWithCGImage:CGImageCreateWithImageInRect(image.CGImage, rect)];
    UIGraphicsEndImageContext();
    return image;
}

@end

我在这里设置了一个断点:

运行:

• 这是view-self:(来自 OpenGL 渲染的图片)

  

• 这是生成的图片:

  

为什么是黑图？

Answer 1

当使用 OpenGL (ES) 时，是的，我假设您正在使用 OpenGL ES，因为您有一个 UIView 类别，请记住在呈现渲染缓冲区之前捕获屏幕。一旦您或 GLKViewController 的子类呈现渲染缓冲区，它就变成了前帧缓冲区，然后屏幕帧缓冲区变成了后帧缓冲区，除了您使用 glClearColor 设置的颜色之外，它什么也没有给您。

[EAGLContext presentRenderbuffer:]

这里是截屏的示例代码。

- (UIImage *)createImageFromFramebuffer {
    GLint params[10];
    glGetIntegerv(GL_VIEWPORT, params);
    int width = params[2];
    int height = params[3];
    const int renderTargetWidth = width;
    const int renderTargetHeight = height;
    const int renderTargetSize = renderTargetWidth*renderTargetHeight * 4;

    uint8_t* imageBuffer = (uint8_t*)malloc(renderTargetSize);
    glReadPixels(params[0], params[1],
             renderTargetWidth, renderTargetHeight,
             GL_RGBA, GL_UNSIGNED_BYTE, imageBuffer);

    const int rowSize = renderTargetWidth*4;

    CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, imageBuffer, renderTargetSize, NULL);
    CGImageRef iref = CGImageCreate(renderTargetWidth, renderTargetHeight, 8, 32, rowSize,
                                CGColorSpaceCreateDeviceRGB(),
                                kCGImageAlphaLast | kCGBitmapByteOrderDefault, ref,
                                NULL, true, kCGRenderingIntentDefault);

    uint8_t* contextBuffer = (uint8_t*)malloc(renderTargetSize);
    memset(contextBuffer, 0, renderTargetSize);
    CGContextRef context = CGBitmapContextCreate(contextBuffer, renderTargetWidth, renderTargetHeight, 8, rowSize,
                                             CGImageGetColorSpace(iref),
                                             kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Big);
    CGContextTranslateCTM(context, 0.0, renderTargetHeight);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextDrawImage(context, CGRectMake(0.0, 0.0, renderTargetWidth, renderTargetHeight), iref);
    CGImageRef outputRef = CGBitmapContextCreateImage(context);

    UIImage* image = [[UIImage alloc] initWithCGImage:outputRef];

    CGImageRelease(outputRef);
    CGContextRelease(context);
    CGImageRelease(iref);
    CGDataProviderRelease(ref);

free(contextBuffer);
    free(imageBuffer);
    return image;
}