Question

我几乎逐字地使用了来自http://developer.apple.com/library/ios/#qa/qa1714/_index.html的示例代码，我可以保存我的背景图片或叠加层，但我无法将两者结合起来。当我尝试使用以下代码组合它们时，叠加层渲染背景为白色，我假设它覆盖了背景。知道为什么会这样吗？

这是我尝试将视图叠加层与图像组合的方法：

-(void) annotateStillImage
{
    UIImage *image = stillImage;

    // Create a graphics context with the target size
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);

    CGContextRef context = UIGraphicsGetCurrentContext();


    // Draw the image returned by the camera sample buffer into the context. 
    // Draw it into the same sized rectangle as the view that is displayed on the screen.
    UIGraphicsPushContext(context);

    [image drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    UIGraphicsPopContext();

    // -renderInContext: renders in the coordinate space of the layer,
    // so we must first apply the layer's geometry to the graphics context
    CGContextSaveGState(context);
    // Center the context around the window's anchor point
    CGContextTranslateCTM(context, [[self view] center].x, [[self view] center].y);
    // Apply the window's transform about the anchor point
    CGContextConcatCTM(context, [[self view] transform]);
    // Offset by the portion of the bounds left of and above the anchor point
    CGContextTranslateCTM(context,
                          -[[self view] bounds].size.width * [[[self view] layer] anchorPoint].x,
                          -[[self view] bounds].size.height * [[[self view] layer] anchorPoint].y);

    // Render the layer hierarchy to the current context
    [[[self view] layer] renderInContext:context];

    // Restore the context
    CGContextRestoreGState(context);

    // Retrieve the screenshot image containing both the camera content and the overlay view
    stillImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
}

以下是我的方法的一个片段，它会在相关的情况下创建视图：

CGRect layerRect = [[[self view] layer] bounds];
[[self previewLayer] setBounds:layerRect];
[[self previewLayer] setPosition:CGPointMake(CGRectGetMidX(layerRect),  CGRectGetMidY(layerRect))];
[[[self view] layer] addSublayer:[self previewLayer]];

UIButton *overlayButton = [UIButton buttonWithType:UIButtonTypeCustom];
[overlayButton setImage:[UIImage imageNamed:@"acceptButton.png"] forState:UIControlStateNormal];
[overlayButton setFrame:[self rectForAcceptButton] ];
[overlayButton setAutoresizesSubviews:TRUE];
[overlayButton setAutoresizingMask:UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleLeftMargin];
[overlayButton addTarget:self action:@selector(acceptButtonPressed) forControlEvents:UIControlEventTouchUpInside];
[[self view] addSubview:overlayButton];

我希望annotate方法中的图像是背景，并且视图中的accept按钮将添加到顶部。我得到的只是接受按钮和白色背景，但如果我不运行renderInContext方法，我得到的只是图像背景而没有叠加。

谢谢！

Answer 1

原来我将叠加层添加到与预览图层相同的视图中，而不是将其放在自己的视图中。我通过回顾这个涵盖所有类型屏幕截图的伟大项目来实现这一点：https://github.com/cocoacoderorg/Screenshots

修复是在具有透明背景的IB中创建单独的叠加视图，并将我的叠加元素添加到此。

通过使用renderInContext在UIImage上绘制UIView来截取屏幕截图时，我的UIImage不会显示

1 个答案: