目標C：如何在四邊形曲線中繪制帶有alpha的線

Question

我在使用四邊形曲線點時遇到點麻煩。.我想為線條設置不透明度，但我也看到點在這里，這是我的代碼。

CGPoint midPoint(CGPoint p1,CGPoint p2)
{
    return CGPointMake ((p1.x + p2.x) * 0.5,(p1.y + p2.y) * 0.5);
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event//upon touches
{
    UITouch *touch = [touches anyObject];

    previousPoint1 = [touch locationInView:self.view];
    previousPoint2 = [touch locationInView:self.view];
    currentTouch = [touch locationInView:self.view];
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event//upon moving
{
    UITouch *touch = [touches anyObject];

    previousPoint2 = previousPoint1;
    previousPoint1 = currentTouch;
    currentTouch = [touch locationInView:self.view];

    CGPoint mid1 = midPoint(previousPoint2, previousPoint1); 
    CGPoint mid2 = midPoint(currentTouch, previousPoint1);

    UIGraphicsBeginImageContext(CGSizeMake(1024, 768));
    [imgDraw.image drawInRect:CGRectMake(0, 0, 1024, 768)];
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineCap(context,kCGLineCapRound);
    CGContextSetLineWidth(context, slider.value);
    CGContextSetBlendMode(context, blendMode);
    CGContextSetRGBStrokeColor(context,red, green, blue, 0.5);
    CGContextBeginPath(context);
    CGContextMoveToPoint(context, mid1.x, mid1.y);
    CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
    CGContextStrokePath(context);

    imgDraw.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsGetCurrentContext();
    endingPoint=currentTouch;
}

任何答案將不勝感激。

Answer 1

您需要做的是保留用戶迄今為止輸入的所有點的列表，並始終將所有點重新繪制為同一路徑的一部分。

您將需要一個數組來存儲點。類似

CGPoint points[kMaxNumPoints];

而不是previousPoint1 / 2等。然后在touchesMoved: ，您將循環遍歷各個點。 像這樣：

CGContextBeginPath (context);
CGContextMoveToPoint (context, points [ 0 ].x, point [ 0 ].y);
for (int i = 1; i < currNumPoints; i++) 
{
    // I wasn't sure from your example if you wanted the mid point here instead of the 
    // previous point. But you get the idea.
    CGContextAddQuadCurveToPoint (context, points [ i - 1 ].x, points [ i - 1 ].y, point [ i ].x, point [ i ].y);
}
CGContextStrokePath (context);