Vertical Text Alignment in Core Text - ios

Question

EDIT: Here's a Github Gist of the below code if that is more readable.
I'm writing a method to draw text within a rectangle in a PDF using Core Text. What I've written accomplishes everything I need, except vertical alignment (top, center, bottom). The standard way that the text is currently drawn is the top, and I specifically need the bottom alignment.
- (void)drawText:(NSString *)textToDraw inFrame:(CGRect)frameRect withFont:(UIFont *)originalFont textColor:(UIColor *)textColor alignment:(PDFTextAlignment)alignment verticalAlignment:(PDFTextVerticalAlignment)verticalAlignment {
if (!textToDraw) {
// If nil, give it an empty value to draw
textToDraw = #"";
}
// Prepare font
CTFontRef font = [self ctFontRefFromUIFont:originalFont];
CGColorRef color = textColor.CGColor;
// Paragraph
CTTextAlignment ctAlignment;
switch (alignment) {
case PDFTextAlignmentLeft:
ctAlignment = kCTTextAlignmentLeft;
break;
case PDFTextAlignmentCenter:
ctAlignment = kCTTextAlignmentCenter;
break;
case PDFTextAlignmentRight:
ctAlignment = kCTTextAlignmentRight;
break;
case PDFTextAlignmentJustified:
ctAlignment = kCTTextAlignmentJustified;
break;
default:
ctAlignment = kCTTextAlignmentLeft;
break;
}
CTParagraphStyleSetting settings[] = {
{kCTParagraphStyleSpecifierAlignment, sizeof(ctAlignment), &ctAlignment},
};
CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(settings, sizeof(settings) / sizeof(settings[0]));
// Create an attributed string
CFStringRef keys[] = { kCTFontAttributeName, kCTForegroundColorAttributeName, kCTParagraphStyleAttributeName };
CFTypeRef values[] = { font, color, paragraphStyle };
CFDictionaryRef attr = CFDictionaryCreate(NULL, (const void **)&keys, (const void **)&values,
sizeof(keys) / sizeof(keys[0]), &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
CFStringRef stringRef = (__bridge CFStringRef)textToDraw;
// Prepare the text using a Core Text Framesetter.
CFAttributedStringRef currentText = CFAttributedStringCreate(NULL, stringRef, attr);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(currentText);
CGMutablePathRef framePath = CGPathCreateMutable();
CGPathAddRect(framePath, NULL, frameRect);
// Get the frame that will do the rendering.
CFRange currentRange = CFRangeMake(0, 0);
CTFrameRef frameRef = CTFramesetterCreateFrame(framesetter, currentRange, framePath, NULL);
CGPathRelease(framePath);
// Get the graphics context.
CGContextRef currentContext = UIGraphicsGetCurrentContext();
// Put the text matrix into a known state. This ensures
// that no old scaling factors are left in place.
CGContextSetTextMatrix(currentContext, CGAffineTransformIdentity);
// Core Text draws from the bottom-left corner up, so flip
// the current transform prior to drawing.
// Modify this to take into consideration the origin.
CGContextTranslateCTM(currentContext, 0, frameRect.origin.y*2);
CGContextScaleCTM(currentContext, 1.0, -1.0);
// Draw the frame.
CTFrameDraw(frameRef, currentContext);
// Add these two lines to reverse the earlier transformation.
CGContextScaleCTM(currentContext, 1.0, -1.0);
CGContextTranslateCTM(currentContext, 0, (-1)*frameRect.origin.y*2);
CFRelease(frameRef);
CFRelease(stringRef);
CFRelease(framesetter);
CFRelease(font);
CFRelease(paragraphStyle);
}
Here is an example of how this will currently draw text in a rectangle (note the rectangle drawn with the lines is the same frameRect I'm passing in)...
.
I want this text to appear as bottom aligned in this rectangle, like this...
.
I've gone through the solutions on this SO post, but have not had any luck getting the text to align correctly.
I'm passing in an enumerated value for the vertical alignment, so ideally I will determine the vertical alignment with the following conditional.
if (verticalAlignment == PDFTextVerticalAlignmentTop) {
// Top align
} else if (verticalAlignment == PDFTextVerticalAlignmentCenter) {
// Center (vertical) align
} else if (verticalAlignment == PDFTextVerticalAlignmentBottom) {
// Bottom align
} else {
// Default: Bottom alignment
}
Thanks!

Answer 1

As I am not quite sure how you approached the solutions from the linked post, I will suggest a solution based on one of those answers. This may be exactly what you tried, but it may also be the appropriate solution.
I assume a method exists for obtaining the size of CTFrameRef, leaving that implementation to you, as long as the appropriate CGSize is returned. Apart from the methods shown in the linked SO post, it might also be worth looking at CTFramesetterSuggestFrameSizeWithConstraints. Assuming this function is available, it should be enough to adjust this part of the drawing function
...
CGMutablePathRef framePath = CGPathCreateMutable();
// Get the graphics context.
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGRect textRect = frameRect; // Will also give you the default behavior for top align
CGSize textSize = [self measureFrame:frameref forContext:currentContext];
if (verticalAlignment == PDFTextVerticalAlignmentBottom) {
// Bottom align
textRect.size.height = textSize.height;
textRect.origin.y = frameRect.origin.y + frameRect.size.height - textSize.height;
} else if (verticalAlignment == PDFTextVerticalAlignmentCenter) {
// Center (vertical) align
textRect.size.height = textSize.height;
textRect.origin.y = frameRect.origin.y + (frameRect.size.height - textSize.height) / 2;
}
CGPathAddRect(framePath, NULL, textRect);
...