CALayer 和离屏渲染

发布于 2024-09-26 05:10:15 字数 703 浏览 7 评论 0原文

我有一个 Paging UIScrollView ，其 contentSize 足够大，可以容纳许多用于缩放的小型 UIScrollView，viewForZoomingInScrollView 是一个 viewController，它容纳一个用于在其上绘制 PDF 页面的 CALayer。这使我能够像 ibooks PDF 阅读器一样浏览 PDF。

绘制 PDF（平铺图层）的代码位于：

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx;

并且只需将“页面”添加到可见屏幕即可自动调用此方法。当我更改页面时，即使已经创建了对象（页面），在绘制所有图块之前也会有一些延迟。

我想要做的是在用户滚动到下一页之前渲染下一页，从而防止可见的平铺效果。但是，我发现如果图层位于屏幕外，将其添加到滚动视图不会调用drawLayer。

这里有什么想法/常见问题吗？

我已经尝试过：

[viewController.view.layer setNeedsLayout]; 
[viewController.view.layer setNeedsDisplay];

注意：在功能上复制 ibook 的事实与完整应用程序的上下文无关。

原文

I have a Paging UIScrollView with a contentSize large enough to hold a number of small UIScrollViews for zooming, The viewForZoomingInScrollView is a viewController that holds a CALayer for drawing a PDF page onto. This allows me to navigate through a PDF much like the ibooks PDF reader.

The code that draws the PDF (Tiled Layers) is located in:

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx;

And simply adding a 'page' to the visible screen calls this method automatically. When I change page there is some delay before all the tiles are drawn, even though the object (page) has already been created.

What i want to be able to do is render the next page before the user scrolls to it, thus preventing the visible tiling effect. However, i have found that if the layer is located offscreen adding it to the scrollview doesn't call the drawLayer.

Any Ideas/common gotchas here?

I have tried:

[viewController.view.layer setNeedsLayout]; 
[viewController.view.layer setNeedsDisplay];

NB: The fact that this is replicating the ibooks functionally is irrelevant within the context of the full app.

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为你鎻心 2024-10-03 05:10:15

正如我上面提到的，如果 CALayers 位于屏幕外，则它们不会渲染。

我最终没有将 PDF 直接绘制到图层上，而是在需要时将 PDF 页面渲染为图像（渲染 1 页加上和减去焦点页面之一）

以下是渲染代码：

-(UIImage *)renderPDFPageToImage:(int)pageNumber//NSOPERATION?
{
 //you may not want to permanently (app life) retain doc ref

 CGSize size = CGSizeMake(x,y);     
 UIGraphicsBeginImageContext(size);
 CGContextRef context = UIGraphicsGetCurrentContext();

 CGContextTranslateCTM(context, 0, 750);
 CGContextScaleCTM(context, 1.0, -1.0);

 CGPDFPageRef page;  //Move to class member 

    page = CGPDFDocumentGetPage (myDocumentRef, pageNumber);
    CGContextDrawPDFPage (context, page);

 UIImage * pdfImage = UIGraphicsGetImageFromCurrentImageContext();//autoreleased
 UIGraphicsEndImageContext();
 return pdfImage;

}

As i mentioned above, CALayers don't render if they are offscreen.

I ended up not drawing the PDF directly to the layer but instead, rendered the PDF page to an image when i needed (renders 1 page plus and minus one of the focused page)

Here is the render code:

-(UIImage *)renderPDFPageToImage:(int)pageNumber//NSOPERATION?
{
 //you may not want to permanently (app life) retain doc ref

 CGSize size = CGSizeMake(x,y);     
 UIGraphicsBeginImageContext(size);
 CGContextRef context = UIGraphicsGetCurrentContext();

 CGContextTranslateCTM(context, 0, 750);
 CGContextScaleCTM(context, 1.0, -1.0);

 CGPDFPageRef page;  //Move to class member 

    page = CGPDFDocumentGetPage (myDocumentRef, pageNumber);
    CGContextDrawPDFPage (context, page);

 UIImage * pdfImage = UIGraphicsGetImageFromCurrentImageContext();//autoreleased
 UIGraphicsEndImageContext();
 return pdfImage;

}

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