ios - iOS平台如何画线

Question

我用的是竹书、纸之类的app，在iPad上，体验真的很好，效果如何？在屏幕上绘制直线或曲线时使用了哪种技术？

Answer 1

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];

    if ([touch tapCount] == 2) {
        //self.imageView.image = nil;
        return;
    }

    lastPoint = [touch locationInView:self.view];
    lastPoint.y -= 20;

}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    mouseSwiped = YES;

    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];
    currentPoint.y -= 20;

    CGFloat components[3];
    [self getRGBComponents:components forColor:self.colorView.backgroundColor];
    NSLog(@"%f %f %f", components[0], components[1], components[2]);

    UIGraphicsBeginImageContext(self.view.frame.size);
    [self.imageView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10.0);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2],5.0);
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);


        CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeNormal);


    CGContextStrokePath(UIGraphicsGetCurrentContext());
    self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;

    mouseMoved++;

    if (mouseMoved == 10) {
        mouseMoved = 0;
    }

}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];

    if ([touch tapCount] == 2) {
        //self.imageView.image = nil;
        return;
    }


    if(!mouseSwiped) {

        CGFloat components[3];
        [self getRGBComponents:components forColor:self.colorView.backgroundColor];
        NSLog(@"%f %f %f", components[0], components[1], components[2]);

        UIGraphicsBeginImageContext(self.view.frame.size);
        [self.imageView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], 5.0);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
}

另请检查以下链接

http://www.techotopia.com/index.php/An_iOS_4_iPhone_Graphics_Drawing_Tutorial_using_Quartz_2D

https://stackoverflow.com/questions/6449661/drawing-2d-images-on-iphone-tutorials

http://mobile.tutsplus.com/tutorials/iphone/ios-sdk_freehand-drawing/

http://www.raywenderlich.com/18840/how-to-make-a-simple-drawing-app-with-uikit