使用CGContextDrawPDFPage繪製PDF頁面後重新設置CGContextRef

我想爲PDF文檔中的每個PDF頁面創建縮略圖並將其放置在UISCrollVIew中。我在這方面取得了成功，但當速度太快時，滾動並不像我想要的那麼順利。我想優化創建PDF頁面的拇指圖像。我想在CGContextDrawPDFPage之後創建一個CGContextRef並重置它的內容，因此我不必每次創建一個上下文並執行一些其他計算，這需要大量資源。使用CGContextDrawPDFPage繪製PDF頁面後重新設置CGContextRef

重置CGContextDrawPDFPage後的CGContextRef內容是否可能？ CGContextRestoreGState和CGContextSaveGState在這種情況下似乎沒有幫助。

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; 
GCPdfSource *pdfSource = [GCPdfSource sharedInstance]; 
for (int i = pageRange.location; i <= pageRange.length; i++) { 

    UIView *thumbPdfView = [scrollView viewWithTag:i+1]; 
    if (thumbPdfView == nil) { 

     CGPDFPageRef pdfPage = [pdfSource pageAt:i + 1]; 
     float xPosition = THUMB_H_PADDING + THUMB_H_PADDING * i + THUMB_WIDTH * i; 

     CGRect frame = CGRectMake(xPosition, THUMB_H_PADDING, THUMB_WIDTH, THUMB_HEIGHT); 
     thumbPdfView = [[UIView alloc] initWithFrame:frame]; 
     thumbPdfView.opaque = YES; 
     thumbPdfView.backgroundColor = [UIColor whiteColor]; 
     [thumbPdfView setTag:i+1]; 

     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
     CGContextRef context = CGBitmapContextCreate(NULL, 
             frame.size.width, 
             frame.size.height, 
             8,      /* bits per component*/ 
             frame.size.width * 4, /* bytes per row */ 
             colorSpace, 
             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); 
     CGColorSpaceRelease(colorSpace); 
     CGContextClipToRect(context, CGRectMake(0, 0, frame.size.width,frame.size.height)); 


     CGRect pdfPageRect = CGPDFPageGetBoxRect(pdfPage, kCGPDFMediaBox); 
     CGRect contextRect = CGContextGetClipBoundingBox(context); 
     CGAffineTransform transform = aspectFit(pdfPageRect, contextRect); 

     CGContextConcatCTM(context, transform); 
     CGContextDrawPDFPage(context, pdfPage); 


     CGImageRef image = CGBitmapContextCreateImage(context); 
     CGContextRelease(context); 
     UIImage *uiImage = [[UIImage alloc]initWithCGImage:image]; 
     CGImageRelease(image); 

     UIImageView *imageVIew = [[UIImageView alloc]initWithImage:uiImage]; 
     [uiImage release]; 

     [thumbPdfView addSubview:imageVIew]; 
     [imageVIew release]; 

     [scrollView addSubview:thumbPdfView]; 
     [thumbPdfView release]; 

    } 
} 

[pool release];//release

和aspectFit功能...

CGAffineTransform aspectFit(CGRect innerRect, CGRect outerRect) { 
CGFloat scaleFactor = MIN(outerRect.size.width/innerRect.size.width, outerRect.size.height/innerRect.size.height); 
CGAffineTransform scale = CGAffineTransformMakeScale(scaleFactor, scaleFactor); 
CGRect scaledInnerRect = CGRectApplyAffineTransform(innerRect, scale); 
CGAffineTransform translation = 
CGAffineTransformMakeTranslation((outerRect.size.width - scaledInnerRect.size.width)/2 - scaledInnerRect.origin.x, 
           (outerRect.size.height - scaledInnerRect.size.height)/2 - scaledInnerRect.origin.y); 
return CGAffineTransformConcat(scale, translation);

}

來源

2010-07-09 Koteg

嘗試CGContextClearRect(context, contextBounds)。

CGContextSaveGState和CGContextRestoreGState對上下文的內容沒有任何影響。他們推動並彈出對上下文狀態方面所做的更改，例如當前的填充顏色。

來源

2010-07-09 10:16:38 Ken

謝謝！它的工作原理，現在我不需要每次繪製pdf頁面時創建一個上下文:) CGContextClearRect（context，CGContextGetClipBoundingBox（context））; 它並沒有像我期望的那樣有幫助（它在滾動速度太快時不太順利），但無論如何它比以前更好。 – Koteg 2010-07-09 12:27:02

使用CGContextDrawPDFPage繪製PDF頁面後重新設置CGContextRef

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