Objective-c: How to rotate CGRect

Question

I\'ve tried to rotate my rectangle, but it does not work properly.

Here is part of my code, I found it in another post:

#define DEGREES_TO_RADIANS(x)         


        

Answer 1

As others have said, an NSRect or CGRect is always an axis-aligned rectangle. CGRectApplyAffineTransform returns the axis-aligned bounding box of the translated rectangle:

Note that the new rectangle (the bounding box) is likely to have different dimensions than the original rectangle, if you applied a rotation. This means it's useless to apply a transform to a rectangle if you want to draw the transformed rectangle.

Instead, you need to transform the coordinate system of the graphics context. Think of it like this: you're drawing on a sheet of paper on a desk. You always draw a rectangle that is aligned to the edges of the desk. To draw a rotated rectangle, you rotate the paper, then draw a rectangle as usual. Changing the CTM is like rotating (or moving or shrinking or expanding) the sheet of paper.

-(void)drawRect:(NSRect)rect {
    CGContextRef gc = [[NSGraphicsContext currentContext] graphicsPort];

    // points[] - this is a CGPoints array, length_one is a double value
    CGRect rect = CGRectMake(points[0].x, points[0].y, (CGFloat)length_one, 40);

    CGFloat xMid = CGRectGetMidX(rect);
    CGFloat yMid = CGRectGetMidY(rect);

    CGContextSaveGState(gc); {
        // Translate the origin to the midpoint of the rectangle, because rotations
        // always happen around the origin.
        CGContextTranslateCTM(gc, xMid, yMid);

        // Rotate the coordinate system by 10 degrees.
        CGContextRotateCTM(gc, 10 * M_PI / 180);

        // Prepare a new rectangle, with the same size as the original rectangle
        // but centered on the origin.
        CGRect newRect = rect;
        newRect.origin.x = -newRect.size.width / 2;
        newRect.origin.y = -newRect.size.height / 2;

        // Add the rectangle to the context's path.
        CGContextAddRect(gc, newRect);

        // Draw the new rectangle.
        CGContextSetFillColorWithColor(gc, [NSColor lightGrayColor].CGColor);
        CGContextSetStrokeColorWithColor(gc, [NSColor blackColor].CGColor);
        CGContextSetLineWidth(gc, 2);
        CGContextSetLineJoin(gc, kCGLineJoinMiter);
        CGContextDrawPath(gc, kCGPathFillStroke);
    } CGContextRestoreGState(gc);

}

Answer 2

override func drawRect(rect: CGRect) {
    super.drawRect(rect)
    let context : CGContextRef = UIGraphicsGetCurrentContext()
    var rect = CGRectMake(100, 100, 120, 180)
    CGContextSaveGState(context);
    var path :CGMutablePathRef  = CGPathCreateMutable();
    var midX : CGFloat = CGRectGetMidX(rect);
    var midY : CGFloat = CGRectGetMidY(rect);
    var transfrom: CGAffineTransform  =
    CGAffineTransformConcat(
        CGAffineTransformConcat(CGAffineTransformMakeTranslation(-midX, -midY),CGAffineTransformMakeRotation(0.3)),
        CGAffineTransformMakeTranslation(midX, midY));
    CGPathAddRect(path, &transfrom, rect);
    CGContextSetFillColorWithColor(context, UIColor.blueColor().CGColor);
    CGContextAddPath(context, path);
    CGContextFillPath(context);
    CGContextRestoreGState(context);
}