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POreseting CGContextRef after drawing pdf page using CGContextDrawPDFPage
 

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  1. POreseting CGContextRef after drawing pdf page using CGContextDrawPDFPage
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    <p>I am trying to create thumb images for every pdf page in PDF document and place it in a UISCrollVIew. I have succeeded in this, but scrolling is not so smooth as I want when it's too fast. And I want to optimize thumb images creating for Pdf page. I want to create one CGContextRef and reset its content after CGContextDrawPDFPage, as a consequence I wouldn't have to create a context each time and perform some other calculation, which takes a lot of resources.</p> <p>Is it possible to reset CGContextRef content after CGContextDrawPDFPage? CGContextRestoreGState and CGContextSaveGState seems to doesn't help in this situation.</p> <pre><code>NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; GCPdfSource *pdfSource = [GCPdfSource sharedInstance]; for (int i = pageRange.location; i &lt;= 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 </code></pre> <p>and aspectFit function...</p> <pre><code>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); </code></pre> <p>}</p>
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