In the process of updating my iPad app I've been attempting to draw a page from an existing PDF document into a Core Graphics context then save it as a new PDF, but am having difficulty getting the text to display properly. Images in the newly-created PDF look great, but text rarely appears correctly: more often that not it appears white/invisible or garbled. When the text is invisible, I am still able to to select where it -should- be and copy/paste correctly into a text editor. Is this an issue related to the limited number of fonts available on the iPad?
My code is as follows:
CGPDFDocumentRef document = CGPDFDocumentCreateWithProvider(dataProvider);
CGPDFPageRef page = CGPDFDocumentGetPage(document, pageNumberToRetrieve);
CGRect pageRect = CGPDFPageGetBoxRect(page, kCGPDFMediaBox);
UIGraphicsBeginPDFContextToFile(pathToFile, pageRect, nil);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextBeginPage(context, NULL);
// I don't think this line is necessary, but I have tried both with and without it.
CGContextSetTextDrawingMode (context, kCGTextFill);
CGContextDrawPDFPage(context, page);
CGContextEndPage(context);
UIGraphicsEndPDFContext();
CGDataProviderRelease(dataProvider);
CGPDFDocumentRelease(document);
If anyone has any suggestions I would greatly appreciate hearing them.
Thanks for your time.
Rob
Drawing into an image context does not pose a problem (text displays correctly).
What I am trying to do is create a -new- PDF file containing just a few pages from the original PDF. It seems that text does not draw correctly into the new file for some reason.
The information is there (I can select text by 'guessing' where it should be in Preview) but it doesn't render. I assume CGContextDrawPDFPage writes the string to the PDF file, but doesn't draw it because it doesn't know what the characters of that font 'look like'?
I thought the point of embedded fonts in PDFs was that programs would be able to perform these sorts of manipulations even if that font wasn't installed on the system (in this case, the iPad). Is this a limitation of the format, or the Quartz framework?
Do you want to render on the screen? I don't see the need for UIGraphicsBeginPDFContextToFile?
However, to render on the screen, you can use something like this:
pageReference = CGPDFDocumentGetPage(pdfReference, page);
CGContextRef context = UIGraphicsGetCurrentContext();
#try {
CGContextTranslateCTM(context, 0.0, self.bounds.size.height);
CGContextScaleCTM(context, scale, -scale);
CGContextSaveGState(context);
#try {
CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(pageReference, kCGPDFCropBox, self.bounds, 0, true);
CGContextConcatCTM(context, pdfTransform);
CGContextDrawPDFPage(context, pageReference);
}
#finally {
CGContextRestoreGState(context);
}
}
#finally {
UIGraphicsEndImageContext();
}
Related
i've been hammering my brain trying to figure this one out and can't find anything in the doc's or on SO that is helpful so far. i have a project that allows the user the input data and save it to a plist. is there a way to display the data that has been stored in the plist in a new view in pdf format? what i am trying to do is to display the recorded data in a new view controller with pdf format so the user can print that list. i know there is a way but i just can't figure it out and i finally threw the towel in and here i am. i will be eternally grateful for any help guys. and girls too.
i can create a new pdf with the following code. i just can't seem to understand how to get the eta from the plist to display.
- (IBAction)didClickMakePDF {
[self setupPDFDocumentNamed:#"NewPDF" Width:850 Height:1100];
[self beginPDFPage];
CGRect textRect = [self addText:#"This is some nice text here, don't you agree?"
withFrame:CGRectMake(kPadding, kPadding, 400, 200) fontSize:48.0f];
CGRect blueLineRect = [self addLineWithFrame:CGRectMake(kPadding, textRect.origin.y + textRect.size.height + kPadding, _pageSize.width - kPadding*2, 4)
withColor:[UIColor blueColor]];
UIImage *anImage = [UIImage imageNamed:#"tree.jpg"];
CGRect imageRect = [self addImage:anImage
atPoint:CGPointMake((_pageSize.width/2)-(anImage.size.width/2), blueLineRect.origin.y + blueLineRect.size.height + kPadding)];
[self addLineWithFrame:CGRectMake(kPadding, imageRect.origin.y + imageRect.size.height + kPadding, _pageSize.width - kPadding*2, 4)
withColor:[UIColor redColor]];
[self finishPDF];
}
So, you've got your PDF context and some text loaded from your plist. You need to decide how it will be laid out to be rendered into the PDF. Core Text can make a really nice job of it. The quick and easy route to get you started is:
start by flipping the context
CGContextScaleCTM(pdfContext, 1.0, -1.0);
CGContextTranslateCTM(pdfContext, 0.0, -bounds.size.height);
draw your text
[text drawAtPoint:CGPointMake(x, y) withFont:[UIFont boldSystemFontOfSize:48.0f]];
where you will obviously want to change:
the text content in a loop
the y position so each line is drawn further down the page
the font
Images can be drawn into the context in the same way.
Then, move on to Core Text to do a better job with paragraphs of text.
"When you draw to the PDF context using CGContext functions the drawing operations are recorded in PDF format. The PDF commands that represent the drawing are written to the destination specified when you create the PDF graphics context."
This comes from the same page referenced above: https://developer.apple.com/library/ios/documentation/GraphicsImaging/Reference/CGPDFContext/Reference/reference.html
A CGPDFContext is "just" a CGContext. You could set a color in it using "CGContextSetCMYKFillColor" for example or draw text in it using the NSString "drawInRect" method.
I'd like to draw an full page image to a PDF but I've always had a hard time wrapping my head around CGContextRefs so I don't know what to make of the error.
Note, this is NOT iOS. I'm making a desktop application.
So far, I have this:
-(void) addImage:(NSURL*) url toPage:(size_t) page toPDF:(CGPDFDocumentRef) pdf
{
NSImage *image = [[NSImage alloc] initWithContentsOfURL:url];
image = [image imageScaledToFitSize:pageSize.size]; //From Matt Gemmell's Crop extensions category
[image lockFocus];
CGContextRef context = [[NSGraphicsContext currentContext] graphicsPort];
[image drawInRect:pageSize];
[image unlockFocus];
CGPDFPageRef pageRef = CGPDFDocumentGetPage(pdf, page);
CGPDFContextBeginPage(context, pageInformation);
CGContextDrawPDFPage(context, pageRef);
CGPDFContextEndPage(context);
}
However, I'm greeted with the error:
CGPDFContextEndPage: invalid context 0x61000017b540. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.
What is wrong with my contexts please?
You need to create and use a CGPDFContext. Different contexts are specific to different rendering processes / destinations so you need to choose the correct one. So look at using CGPDFContextCreateWithURL to create a PDF context to write the data to a file.
I'm creating an app which uses UIImagePickerController to present a camera to the user with a custom overlay which includes one of two grids/patterns over the camera "view" itself.
The grids themselves are .png files in a UIImageView which is added to the overlay, they're quite complex so I would really like to steer away from drawing the grid in code, even though that would present I nice clean and simple answer to my question.
I would like to be able to offer the grids in a variety of colours. The obvious solution is create more .png images in different colours, but for each colour there would have to be four separate images (regular and retina for each of the grids) so that would quickly add up to a lot of assets.
The solution which, I think, would be ideal, would be for me to just create the grids in white/gray and then apply a tint to it to colour it appropriately.
Is that possible? Or do I need to seek an alternative solution?
With thanks to Ananth for pointing me to iPhone - How do you color an image?
I've added this method to my code as suggested in the question, with the modification in willc2's answer:
-(UIImage *)colorizeImage:(UIImage *)baseImage color:(UIColor *)theColor {
UIGraphicsBeginImageContext(baseImage.size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGRect area = CGRectMake(0, 0, baseImage.size.width, baseImage.size.height);
CGContextScaleCTM(ctx, 1, -1);
CGContextTranslateCTM(ctx, 0, -area.size.height);
CGContextSaveGState(ctx);
CGContextClipToMask(ctx, area, baseImage.CGImage);
[theColor set];
CGContextFillRect(ctx, area);
CGContextRestoreGState(ctx);
CGContextSetBlendMode(ctx, kCGBlendModeMultiply);
CGContextDrawImage(ctx, area, baseImage.CGImage);
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
...and I'm getting exactly what I'm after.
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.
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;
}
I have an NSImage that came from a PDF, so it has one representation, of type NSPDFImageRep. I do an image setDataRetained:YES; to make sure that it remains a NSPDFImageRep. Later, I want to change the page, so I get the rep, and set the current page. This is fine.
The problem is that when I draw the image, only the 1st page comes out.
My impression is that when I draw an NSImage, it picks a representation, and draws that representation. Now, the image only has one rep, so that's the one that is being drawn, and that's the PDFrep. So, why when I draw the image, is it not drawing the correct page?
HOWEVER, when I draw the representation itself, I get the correct page.
What am I missing?
NSImage does a caching of the NSImageRep, when first displayed. In the case of NSPDFImageRep, the "setCacheMode:" message has no effect. Thus, the page that will be displayed will always be the first page. See this guide for more information.
You have then two solutions:
Drawing the representation directly.
Call the "recache" message on the NSImage to force the rasterization of the selected page.
An alternative mechanism to draw a PDF is to use the CGPDF* functions. To do this, use CGPDFDocumentCreateWithURL to create a CGPDFDocumentRef object. Then, use CGPDFDocumentGetPage to get a CGPDFPageRef object. You can then use CGContextDrawPDFPage to draw the page into your graphics context.
You may have to apply a transform to ensure that the document ends up sized like you want. Use a CGAffineTransform and CGContextConcatCTM to do this.
Here is some sample code pulled out of one of my projects:
// use your own constants here
NSString *path = #"/path/to/my.pdf";
NSUInteger pageNumber = 14;
CGSize size = [self frame].size;
// if we're drawing into an NSView, then we need to get the current graphics context
CGContextRef context = (CGContextRef)([[NSGraphicsContext currentContext] graphicsPort]);
CFURLRef url = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, (CFStringRef)path, kCFURLPOSIXPathStyle, NO);
CGPDFDocumentRef document = CGPDFDocumentCreateWithURL(url);
CGPDFPageRef page = CGPDFDocumentGetPage(document, pageNumber);
// in my case, I wanted the PDF page to fill in the view
// so we apply a scaling transform to fir the page into the view
double ratio = size.width / CGPDFPageGetBoxRect(page, kCGPDFTrimBox).size.width;
CGAffineTransform transform = CGAffineTransformMakeScale(ratio, ratio);
CGContextConcatCTM(context, transform);
// now we draw the PDF into the context
CGContextDrawPDFPage(context, page);
// don't forget memory management!
CGPDFDocumentRelease(document);