在显示图层之前应用CGAffineTransform [英] Apply CGAffineTransform prior to layer being displayed

问题描述

我正在尝试缩放 AVCaptureVideoPreviewLayer ，以便它从相机显示放大预览;我可以使用 setAffineTransform：CGAffineTransformMakeScale（2.0f，2.0f）来完成这项工作，但只有在屏幕上显示该图层时才能使用。也就是说，除非我在回调期间（在$ code> viewDidAppear CATransaction 中），否则比例变换似乎不会生效c $ c>。

I'm trying to scale an AVCaptureVideoPreviewLayer so it displays a "zoomed in" preview from the camera; I can make this work using setAffineTransform:CGAffineTransformMakeScale(2.0f, 2.0f), but only once the layer is visible on screen. That is, the scale transform doesn't seem to take effect unless I call it (from within a CATransaction) during a callback like viewDidAppear.

我真正想做的是将比例变换应用于之前，使图层变得可见 - 例如在我初始化它并将其添加到 UIView 时 - 但我所有这样做的尝试都证明是徒劳的。如果我在此时设置了变换，然后在可见时尝试将值读回，它似乎确实具有所需的缩放变换集 - 但它对视图没有任何影响。我是iOS编程新手，所以我确信这里有一些基本的东西。任何帮助表示赞赏！

What I'd really like to do is have the scale transform be applied prior to the layer becoming visible--e.g. at the time that I initialize it and add it to the UIView--but all my attempts to do so have proven futile. If I set the transform at this point, and then attempt to read the value back once it is visible, it does appear to have the desired scale transform set -- yet it does not have any effect on the view. I'm new to iOS programming, so I'm sure there's something basic I'm missing here; any help is appreciated!

推荐答案

两种简单的替代方法，一种（更好）适用于iOS 7.x，另一种适用于早期版本iOS：

Two simple alternative approaches, one (better) for iOS 7.x and one for earlier versions of iOS:

float zoomLevel = 2.0f;
if ([device respondsToSelector:@selector(setVideoZoomFactor:)]
    && device.activeFormat.videoMaxZoomFactor >= zoomLevel) {
  // iOS 7.x with compatible hardware
  if ([device lockForConfiguration:nil]) {
    [device setVideoZoomFactor:zoomLevel];
    [device unlockForConfiguration];
  }
} else {
  // Lesser cases
  CGRect frame = captureVideoPreviewLayer.frame;
  float width = frame.size.width * zoomLevel;
  float height = frame.size.height * zoomLevel;
  float x = (frame.size.width - width)/2;
  float y = (frame.size.height - height)/2;
  captureVideoPreviewLayer.bounds = CGRectMake(x, y, width, height);
}

这篇关于在显示图层之前应用CGAffineTransform的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！