Using Multiple CGAffineTransforms On Text Matrix

Question

I am displaying text using Quartz. Here is my code:

    CGContextRef myContext = UIGraphicsGetCurrentContext();
    CGContextSelectFont(myContext, "Helvetica", 12, kCGEncodingMacRoman);
    CGContextSetCharacterSpacing(myContext, 8);
    CGContextSetTextDrawingMode(myContext, kCGTextFillStroke);
    CGContextSetRGBFillColor(myContext, 0, 0, 0, 1);
    CGContextSetRGBStrokeColor(myContext, 0, 0, 0, 1);
    CGContextSetTextMatrix(myContext,CGAffineTransformMake(1, 0, 0, -1, 0, 0));
    CGContextShowTextAtPoint(myContext, textOrigin.x, textOrigin.y,[way.name UTF8String],[way.name length]);

This displays my text the right way up and in the right direction, however I also need to add a rotation to the text using CGAffineTransformMakeRotation(angle);. I can't seem to work out how to aply two affine transforms to the text matrix, though, without one overwriting the other. Any help would be great.

Answer 1

You can combine matrices with CGAffineTransformConcat, e.g.

CGAffineTransform finalTransf = CGAffineTransformConcat(t1, t2);

If you just need to apply rotation to an existing matrix, use CGAffineTransformRotate, e.g.

CGAffineTransform t = CGAffineTransformMake(1, 0, 0, -1, 0, 0);
CGAffineTransform t = CGAffineTransformRotate(t, M_PI/2);
CGContextSetTextMatrix(myContext, t);

Answer 2

To supplement @kennytm's answer, to apply more than two transforms you can do the following:

var t = CGAffineTransformIdentity
t = CGAffineTransformTranslate(t, CGFloat(100), CGFloat(300))
t = CGAffineTransformRotate(t, CGFloat(M_PI_4))
t = CGAffineTransformScale(t, CGFloat(-1), CGFloat(2))
// ... add as many as you want, then apply it to to the view
imageView.transform = t

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