Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
681 views
in Technique[技术] by (71.8m points)

iphone - Flipped NSString drawing in CGContext

I try to draw a string in this texture:

http://picasaweb.google.it/lh/photo/LkYWBv_S_9v2d6BAfbrhag?feat=directlink

but the green numbers seem vertical flipped. I've created my context in this way:

    colorSpace = CGColorSpaceCreateDeviceRGB();
data = malloc(height * width * 4);
context = CGBitmapContextCreate(data, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

and i've draw the strings:

    UIGraphicsPushContext(context);

for(int i=0;i<packs.size();++i)
{
    CGPoint points[4] = 
    {
        gltextures[i].texCoords[0] * size.width,        //0
        gltextures[i].texCoords[1] * size.height,       //1

        gltextures[i].texCoords[2] * size.width,        //2
        gltextures[i].texCoords[3] * size.height,       //3

        gltextures[i].texCoords[4] * size.width,        //4
        gltextures[i].texCoords[5] * size.height,       //5

        gltextures[i].texCoords[6] * size.width,        //6
        gltextures[i].texCoords[7] * size.height        //7

    };

    CGRect debugRect = CGRectMake
    (
     gltextures[i].texCoords[0] * size.width, 
     gltextures[i].texCoords[1] * size.height, 
     gltextures[i].width, 
     gltextures[i].height
     );
    CGContextSetStrokeColorWithColor(context, [[UIColor redColor] CGColor]);
    CGContextAddLines(context, points, 4);
    CGContextClosePath(context);
    CGContextDrawPath(context, kCGPathStroke);  

    NSString* s = [NSString stringWithFormat:@"%d",gltextures[i].texID];
    UIFont* font = [UIFont fontWithName:@"Arial" size:12];
    CGContextSetRGBFillColor(context, 0, 1, 0, 1);
    [s drawAtPoint:points[0] withFont:font];
}
UIGraphicsPopContext();

The transformation matrix seems the Identity matrix... no CGAffineTransform is applied to THIS context. If the string is flipped, maybe, all my images are flipped! Any suggestion?

PS: sorry for my english ;)

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Answer

0 votes
by (71.8m points)

As describe here, the coordinate system for a context within a UIView or its layer is inverted when compared to the normal Quartz drawing space. However, when using Quartz to draw to an image, this is no longer the case. The UIStringDrawing Cocoa Touch category on NSString that gives you the -drawAtPoint:withFont: method assumes an inverted layout, and that's why you're seeing the flipped text in your image.

One way to work around this would be to save the graphics state, apply an invert transform to the image, draw the text, and restore the old graphics state. This would look something like the following:

CGContextSaveGState(context);
CGContextTranslateCTM(context, 0.0f, self.bounds.size.height);
CGContextScaleCTM(context, 1.0f, -1.0f);

[text drawAtPoint:CGPointMake(0.0f, 0.0f) withFont:font];

CGContextRestoreGState(context);

This is a fairly crude example, in that I believe it just draws the text at the bottom of the image, but you should be able to adjust the translation or the coordinate of the text to place it where it's needed.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...