Portion from CGPDFPage + Scale (zoom)
- by malcom
I wanna take a rect from CGPDFPage (the portion of image around the user's touch point(x,y)) and scale it by a scaleFactor (ie 2x).
Below the code I've used to get CGPDFPage's rect.
The problem with it is the scaleFactor support. The idea is:
1) pageRect size is pageRect.size *2
2) myThumbRect (the region to zoom) become resultImageSize/scaleFactor (because the final output will be scaleFactor times bigger)
3) pointOfClick (x,y) become pointOfClick(2x,2y)
4) scale up the context by factor CGContextScaleCTM(ctx, scaleFactor, -scaleFactor);
5) grab the rect
However the result is an empty image. Any idea?
-(UIImage *) zoomedPDFImageAtPoint:(CGPoint) pointOfClick size:(CGSize) resultImageSize scale:(CGFloat) scaleFactor {
// get the rect of our page
CGRect pageRect = CGPDFPageGetBoxRect(myPageRef, kCGPDFCropBox);
// my thumb rect is a portion of our CGPDFPage with size as /scaleFactor of resultImageSize
// then we need to scale the image portiong by *scaleFactor and draw it in our resultImageSize sized graphic context
CGSize myThumbRect = resultImageSize;
// page rect has size as original size * scaleFactor
//resultImageSize = pageRect.size; // to remove, i've used it to see where the rect is printed in final image
pointOfClick = CGPointMake(-pointOfClick.x, -pointOfClick.y);
NSLog(@"Click (%0.f,%0.f) Page (%0.f,%0.f ; %0.f,%0.f)",pointOfClick.x,pointOfClick.y,pageRect.origin.x,pageRect.origin.y,pageRect.size.width,pageRect.size.height);
// create a new context for resulting image of my desidered size
UIGraphicsBeginImageContext(resultImageSize);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSaveGState(ctx);
// because rect is that for drawing in a flipped coordinate system, this translate the lower-left corner of the rect
// in an upright coordinate system
CGContextTranslateCTM(ctx, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect));
// scale to flip the coordinate system so that the y axis goes up the drawing canvas
CGContextScaleCTM(ctx, 1, -1);
// translate so the origin is offset by exactly the rect origin
CGContextTranslateCTM(ctx, -(pageRect.origin.x), -(pageRect.origin.y));
// zoomRect is interested region.the clickPoint is the center of this region
CGRect zoomedRect = CGRectMake(-pointOfClick.x, (pageRect.size.height-(-pointOfClick.y)),myThumbRect.width,myThumbRect.height);
zoomedRect.origin.y-=(myThumbRect.height/2.0);
zoomedRect.origin.x-=(myThumbRect.width/2.0);
NSLog(@"Zoom region at (%0.f,%0.f) (%0.f,%0.f)",zoomedRect.origin.x,zoomedRect.origin.y,zoomedRect.size.width,zoomedRect.size.height);
// now we need to move clipped rect to the origin
// x: x was moved subtracting current click x coordinate and adding the half of zoomed rect (because zoomedRect contains pointsOfClick at it's center)
// same with y but inverse (because ctm is flipped)
CGPoint translateToOrigin = CGPointMake(pointOfClick.x+(zoomedRect.size.width/2.0), -pointOfClick.y-(zoomedRect.size.height/2.0));//(pageRect.size.height-zoomedRect.size.height)+pointOfClick.y);
NSLog(@"Translate zoomed region to origin using translate by (%0.f,%0.f)",translateToOrigin.x,translateToOrigin.y);
CGContextTranslateCTM(ctx, translateToOrigin.x,translateToOrigin.y);
CGContextClipToRect (ctx, zoomedRect);
// now draw the document
CGContextDrawPDFPage(ctx, myPageRef);
CGContextRestoreGState(ctx);
// generate image
UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return finalImage;
}
