是否可以在 Sprite Kit 中使用圆形(SKShapeNode)作为蒙版?

问题描述

我正在尝试在 Sprite Kit 项目中创建一个圆形蒙版.我像这样创建圆圈(将其定位在屏幕的中心):

I'm trying to create a circular mask in a Sprite Kit project. I create the circle like this (positioning it at the centre of the screen):

SKCropNode *cropNode = [[SKCropNode alloc] init];

SKShapeNode *circleMask = [[SKShapeNode alloc ]init];
CGMutablePathRef circle = CGPathCreateMutable();
CGPathAddArc(circle, NULL, CGRectGetMidX(self.frame), CGRectGetMidY(self.frame), 50, 0, M_PI*2, YES);
circleMask.path = circle;
circleMask.lineWidth = 0;
circleMask.fillColor = [SKColor blueColor];
circleMask.name=@"circleMask";

在代码的下方，我将其设置为 cropNode 的掩码:

and further down the code, I set it as the mask for the cropNode:

[cropNode setMaskNode:circleMask];

...但内容不是显示在圆圈内，而是显示为正方形.

... but instead of the content showing inside a circle, the mask appears as a square.

是否可以使用 SKShapeNode 作为遮罩，还是需要使用图像?

Is it possible to use a SKShapeNode as a mask, or do I need to use an image?

推荐答案

经过大量的咒骂、搜索网络和在 Xcode 中的实验，我有一个非常hacky 的解决方案.

After much swearing, scouring the web, and experimentation in Xcode, I have a really hacky fix.

请记住，这是一个非常讨厌的 hack - 但您可以将其归咎于 Sprite Kit 的 SKShapeNode 实现.向路径添加填充会导致以下情况:

Keep in mind that this is a really nasty hack - but you can blame that on Sprite Kit's implementation of SKShapeNode. Adding a fill to a path causes the following:

• 为您的场景添加一个额外的节点
• 路径变得不可屏蔽 - 它出现在掩码之上"
• 使任何非SKSpriteNode 兄弟节点不可屏蔽(例如SKLabelNodes)

• adds an extra node to your scene
• the path becomes unmaskable - it appears 'over' the mask
• makes any non-SKSpriteNode sibling nodes unmaskable (e.g. SKLabelNodes)

不是一个理想的状态.

灵感来自 Tony Chamblee 的进度计时器，'修复'是完全省去填充，只使用路径的笔划:

Inspired by Tony Chamblee's progress timer, the 'fix' is to dispense with the fill altogether, and just use the stroke of the path:

SKCropNode *cropNode = [[SKCropNode alloc] init];

SKShapeNode *circleMask = [[SKShapeNode alloc ]init];
CGMutablePathRef circle = CGPathCreateMutable();
CGPathAddArc(circle, NULL, CGRectGetMidX(self.frame), CGRectGetMidY(self.frame), 50, 0, M_PI*2, YES); // replace 50 with HALF the desired radius of the circle
circleMask.path = circle;
circleMask.lineWidth = 100; // replace 100 with DOUBLE the desired radius of the circle
circleMask.strokeColor = [SKColor whiteColor];
circleMask.name=@"circleMask";

[cropNode setMaskNode:circleMask];

如上所述，您需要将半径设置为通常的一半，并将线宽设置为半径的两倍.

As commented, you need to set the radius to half of what you'd normally have, and the line width to double the radius.

希望苹果将来会关注这一点；目前，这个 hack 是我找到的最好的解决方案(除了使用图像，如果你的蒙版需要是动态的，这真的不起作用).

Hopefully Apple will look at this in future; for now, this hack is the best solution I've found (other than using an image, which doesn't really work if your mask needs to be dynamic).

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