How do I stroke a CGContext path with multiple random images

问题

I want to stroke a CGContext path using three or four images, but randomly cycle through the images as I'm drawing the path. I want to draw the images INSTEAD!! of drawing the CGContext I am now. I have this code so far

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];
    currentPoint.x = currentPoint.x;
    currentPoint.y = currentPoint.y;
    mouseSwiped = YES;
    UIGraphicsBeginImageContext(self.view.frame.size);
    [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brushSizeVal);
    CGContextSetAlpha(UIGraphicsGetCurrentContext(), drawingColorAlpha);
    CGContextSaveGState(UIGraphicsGetCurrentContext());    //Probably right here
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 
                                                                        drawingColorRed,
                                                                        drawingColorGreen,
                                                                        drawingColorBlue,
                                                                        drawingColorAlpha);
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(),
                                                 lastPoint.x,
                                                 lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), 
                                                  currentPoint.x,
                                                  currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();    //drawImage is the UIImageView that I am drawing my context to
    NSLog(@"current point x: %d current point y: %d",currentPoint.x, currentPoint.y);    //Used for my purposes
    lastPoint = currentPoint;
    mouseMoved++;

and

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{
    if (!optionsDisplayerVisible && canDraw)
     {
        if(!mouseSwiped)
         {
                UIGraphicsBeginImageContext(self.view.frame.size);
                [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
                CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
                CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
                CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brushSizeVal);
                CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 
                                                                   drawingColorRed,
                                                                   drawingColorGreen,
                                                                   drawingColorBlue,
                                                                   drawingColorAlpha);
                CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                CGContextStrokePath(UIGraphicsGetCurrentContext());
                CGContextFlush(UIGraphicsGetCurrentContext());
                drawImage.image = UIGraphicsGetImageFromCurrentImageContext();    //drawImage is the UIImageView that I am drawing to
                UIGraphicsEndImageContext();
         }
     }
}

回答1:

You haven't really explained very clearly what you are trying to do. You are using the word "stroke" while referring to images. You can stroke a path, but not with an image. It doesn't make any sense. You can use an image as a mask and a path that specifies which part of the image to mask. You can do that with CAShapeLayer.

If you are trying to add a new point to a path on each touch, you can just call these two things on the first touchesBegan:

CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(),
                           lastPoint.x,
                           lastPoint.y);

And then call

CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), 
                           currentPoint.x,
                           currentPoint.y);

on subsequent calls to -touchesBegan. Again, I'm not sure exactly what you are trying to do.

One thing to note is that this is not doing anything:

currentPoint.x = currentPoint.x;
currentPoint.y = currentPoint.y;

And I don't see where your mouseSwiped variable is ever getting toggled (set to NO).

来源：https://stackoverflow.com/questions/1943325/how-do-i-stroke-a-cgcontext-path-with-multiple-random-images

标签

iphone

random

png

cgcontext