在多点触控中跟踪触摸点

Question

我正在做一个绘图项目，我想支持多点触控，我已经浏览了在线文档，其中建议跟踪触摸点，我做到了，但我没有得到想要的行为。我没有得到直线。

下面是我的代码

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    red = 0.0/255.0;
    green = 0.0/255.0;
    blue = 0.0/255.0;
    brush = 10.0;
    opacity = 1.0;

     self.view.multipleTouchEnabled = YES;

     touchPaths = [NSMutableDictionary dictionary];
}

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


    for (UITouch *touch in touches)
    {
        NSString *key = [NSString stringWithFormat:@"%d", (int) touch];
        lastPoint = [touch locationInView:self.view];

        [touchPaths setObject:[NSValue valueWithCGPoint:lastPoint] forKey:key];
    }

}


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

    for (UITouch *touch in touches)
    {
        NSString *key = [NSString stringWithFormat:@"%d", (int) touch];

        lastPoint = [[touchPaths objectForKey:key] CGPointValue];


        CGPoint currentPoint1 = [touch locationInView:self.view];

        UIGraphicsBeginImageContext(self.view.frame.size);
        [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint1.x, currentPoint1.y);
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush );
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
        CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal);

        CGContextStrokePath(UIGraphicsGetCurrentContext());
        self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        [self.tempDrawImage setAlpha:opacity];
        UIGraphicsEndImageContext();

        lastPoint = currentPoint1;

    }
}

但是当我使用这段代码绘图时，我明白了。

所以朋友们，请帮帮我，我做错了什么。

问候 兰吉特

Answer 1

我总是尽可能地尝试使用手势识别器。这里我使用UIPanGestureRecognizer：

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.view addGestureRecognizer:[[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(didPan:)]];
}

- (void)didPan:(UIPanGestureRecognizer*)panGesture {
    for (NSUInteger touchIndex = 0; touchIndex < panGesture.numberOfTouches; touchIndex++) {
        // touchIndex is basically the "source" (the finger) from which the point comes from
        CGPoint p = [panGesture locationOfTouch:touchIndex inView:self.view];
        [self drawAtPoint:p withIndex:touchIndex];
    }
}


- (void)drawAtPoint:(CGPoint)point withIndex:(NSUInteger)index{
    UIView *smallPoint = [[UIView alloc] initWithFrame:CGRectMake(point.x, point.y, 3, 3)];
    [smallPoint setBackgroundColor:[self colorForIndex:index]];
    [self.view addSubview:smallPoint];
}

- (UIColor*)colorForIndex:(NSUInteger)index {
    switch (index) {
        case 0: return [UIColor redColor];
        case 1: return [UIColor orangeColor];
        case 2: return [UIColor yellowColor];
        case 3: return [UIColor blueColor];
        case 4: return [UIColor greenColor];
    }
    return [UIColor clearColor];
}

我没有画贝塞尔路径，但是如果你把它放到一个空的 ViewController 中并运行它，你会看到当多点触摸屏幕时，每根手指都会绘制不同的颜色。

因此，如果您考虑到 touchIndex，基本上您可以跟踪不同手指的不同路径。

假设您使用两根手指进行绘图：您将拥有panGesture.numberOfTouches == 2，touchIndex 0 将代表第一根手指，touchIndex 1 将代表第二根手指。您可以将不同数组中的点累积起来，并将这些点添加到它们对应的路径中。

Answer 2

您没有正确填充touchPaths。尝试在每次绘图后设置它，如下所示：

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

    for (UITouch *touch in touches)
    {
        NSString *key = [NSString stringWithFormat:@"%d", (int) touch];

        CGPoint lastPoint = [[touchPaths objectForKey:key] CGPointValue];


        CGPoint currentPoint1 = [touch locationInView:self.view];

        UIGraphicsBeginImageContext(self.view.frame.size);
        [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint1.x, currentPoint1.y);
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush );
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
        CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal);

        CGContextStrokePath(UIGraphicsGetCurrentContext());
        self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        [self.tempDrawImage setAlpha:opacity];
        UIGraphicsEndImageContext();
        // I changed your code here
        [touchPaths setObject:[NSValue valueWithCGPoint:currentPoint1] forKey:key];

    }
}

您当前在此处设置lastPoint，但您似乎没有使用它（而且它只能通过一键式操作）。也不需要将lastPoint 作为字段。