我正在尝试为 PDF 文档中的每个 pdf 页面创建拇指图像并将其放置在 UISCrollVIew 中。我已经成功了,但是当滚动太快时,滚动并没有我想要的那么流畅。我想优化为 Pdf 页面创建的拇指图像。我想创建一个 CGContextRef 并在 CGContextDrawPDFPage 之后重置其内容,因此我不必每次都创建上下文并执行一些其他计算,这会占用大量资源。
是否可以在 CGContextDrawPDFPage 之后重置 CGContextRef 内容?CGContextRestoreGState 和 CGContextSaveGState 在这种情况下似乎没有帮助。
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 函数...
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);
}