![](/img/trans.png)
[英]How can I detect when a user holds their finger over an image in a UIWebView?
[英]how can i fill the transparent area of the image when my finger moved on
我想用畫筆繪制透明區域,但我的代碼工作得不是很好。我想有人可以幫助我。 我的代碼:
// Handles the start of a touch
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
CGRect bounds = [self bounds];
UITouch *touch = [[event touchesForView:self] anyObject];
if (![image isPointTransparent:[touch locationInView:self]]
|| ![image isPointTransparent:[touch previousLocationInView:self]])
{
return;
}
firstTouch = YES;
// Convert touch point from UIView referential to OpenGL one (upside-down flip)
location = [touch locationInView:self];
location.y = bounds.size.height - location.y;
}
// Handles the continuation of a touch.
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
CGRect bounds = [self bounds];
UITouch *touch = [[event touchesForView:self] anyObject];
if (![image isPointTransparent:[touch locationInView:self]]
|| ![image isPointTransparent:[touch previousLocationInView:self]])
{
return;
}
// Convert touch point from UIView referential to OpenGL one (upside-down flip)
if (firstTouch)
{
firstTouch = NO;
previousLocation = [touch previousLocationInView:self];
previousLocation.y = bounds.size.height - previousLocation.y;
}
else
{
location = [touch locationInView:self];
location.y = bounds.size.height - location.y;
previousLocation = [touch previousLocationInView:self];
previousLocation.y = bounds.size.height - previousLocation.y;
}
// Render the stroke
[self renderLineFromPoint:previousLocation toPoint:location];
}
// Handles the end of a touch event when the touch is a tap.
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
CGRect bounds = [self bounds];
UITouch *touch = [[event touchesForView:self] anyObject];
if (![image isPointTransparent:[touch locationInView:self]] || ![image isPointTransparent:[touch previousLocationInView:self]])
{
return;
}
if (firstTouch)
{
firstTouch = NO;
previousLocation = [touch previousLocationInView:self];
previousLocation.y = bounds.size.height - previousLocation.y;
[self renderLineFromPoint:previousLocation toPoint:location];
}
}
重要的是要知道你應該在你的UIView
的drawRect:
做你的實際繪圖。 因此,代碼中的renderLineFromPoint:toPoint:
方法應該只是構建一個行數組並告訴視圖每次重繪,如下所示:
- (void)renderLineFromPoint:(CGPoint)from toPoint:(CGPoint)to
{
[lines addObject:[Line lineFrom:from to:to]];
[self setNeedsDisplay];
}
這假設您有一個具有2個CGPoint
屬性的Line類。 你的drawRect:
可能看起來像這樣:
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(context, 0.0f, 0.0f, 0.0f, 1.0f);
for (Line *line in lines) {
CGContextMoveToPoint(context, line.from.x, line.from.y);
CGContextAddLineToPoint(context, line.to.x, line.to.y);
CGContextStrokePath(context);
}
}
如果你這樣做(沒有OpenGL),就不需要翻轉y軸。
唯一剩下的就是實現isPointTransparent:
方法。 從您的代碼中了解這應該如何工作很難。
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