使用真实分辨率将MKMapView渲染为UIImage [英] Rendering MKMapView to UIImage with real resolution

问题描述

我正在使用此函数将MKMapView实例渲染为图像：

I am using this function for rendering MKMapView instance into image:

@implementation UIView (Ext)
- (UIImage*) renderToImage
{
  UIGraphicsBeginImageContext(self.frame.size);
  [self.layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext(); 
  return image;
}

这很好用。但是对于iphone4，渲染图像的分辨率与设备上的分辨率不同。在设备上，我具有640x920地图视图质量，渲染图像的分辨率为320x460。
然后我将提供给UIGraphicsBeginImageContext（）函数的大小加倍，但填充了唯一的左上角图像部分。

This works fine. But with iphone4 the rendered image doesn't have same resolution as it has really on device. On device I have the 640x920 map view quality, and rendered image has the resolution 320x460. Then I doubled the size that is provided to UIGraphicsBeginImageContext() function but that filled the only top-left image part.

问题：有没有办法将地图渲染成具有全分辨率640x920的图像？

Question: Is there any way to get map rendered to image with full resolution 640x920?

推荐答案

尝试使用 UIGraphicsBeginImageContextWithOptions 而不是 UIGraphicsBeginImageContext ：

UIGraphicsBeginImageContextWithOptions(self.frame.size, NO, 0.0);

参见 QA1703 了解更多详情。它说：

See QA1703 for more details. It says:

注意：从iOS 4开始，
UIGraphicsBeginImageContextWithOptions
允许你提供一个比例
因子。比例因子为零将
设置为设备
主屏幕的比例因子。这使您可以获得
显示的最清晰，最高分辨率的
快照，包括
Retina Display。

Note: Starting from iOS 4, UIGraphicsBeginImageContextWithOptions allows you to provide with a scale factor. A scale factor of zero sets it to the scale factor of the device's main screen. This enables you to get the sharpest, highest-resolustion snapshot of the display, including a Retina Display.

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