ios - Swift SpriteKit 反向掩码不适用于设备，但适用于模拟器

Question

完成此操作的代码非常简单:

var cropNode = SKCropNode()
var shape = SKShapeNode(rectOf: CGSize(width:100,height:100))
shape.fillColor = SKColor.orange

var shape2 = SKShapeNode(rectOf: CGSize(width:25,height:25))
shape2.fillColor = SKColor.red
shape2.blendMode = .subtract
shape.addChild(shape2)

cropNode.addChild(shape)
cropNode.position = CGPoint(x:150,y:170)
cropNode.maskNode=shape
container.addChild(cropNode)

相同的代码，相同的 iOS，不同的结果 = no bueno

Answer 1

这是一个使用着色器为您生成掩码节点的方法:

func generateMaskNode(from mask:SKNode) -> SKNode
{
    var returningNode : SKNode!
    autoreleasepool
    {
        let view = SKView()
        //First let's flatten the node
        let texture = view.texture(from: mask) 
        let node = SKSpriteNode(texture:texture) 
        //Next apply the shader to the flattened node to allow for color swapping
        node.shader = SKShader(fileNamed: "shader.fsh")
        let texture2 = view.texture(from: node)
        returningNode = SKSpriteNode(texture:texture2)

    }
    return returningNode
}

它需要你创建一个名为shader.fsh的文件，里面的代码如下所示:

void main() {

    // Find the pixel at the coordinate of the actual texture
    vec4 val = texture2D(u_texture, v_tex_coord);

    // If the color value of that pixel is 0,0,0
    if (val.r == 0.0 && val.g == 0.0 && val.b == 0.0) {
        // Turn the pixel off
        gl_FragColor  = vec4(0.0,0.0,0.0,0.0);
    } 
    else {
        // Otherwise, keep the original color
        gl_FragColor = val;
    }
}

要使用它，它要求您使用黑色像素而不是 alpha 作为确定裁剪内容的方法，因此您的代码现在应该如下所示:

var cropNode = SKCropNode()
var shape = SKShapeNode(rectOf: CGSize(width:100,height:100))
shape.fillColor = SKColor.orange

var shape2 = SKShapeNode(rectOf: CGSize(width:25,height:25))
shape2.fillColor = SKColor.orange
shape2.blendMode = .subtract
shape.addChild(shape2)

let mask = generateMaskNode(from:shape)

cropNode.addChild(shape)
cropNode.position = CGPoint(x:150,y:170)
cropNode.maskNode=mask
container.addChild(cropNode)

subtract 在模拟器而不是设备上工作的原因是因为模拟器减去了 alpha channel ，而设备却没有。该设备实际上行为正确，因为 alpha 不应该被减去，它应该被忽略。

请注意，您不必选择黑色作为裁剪颜色，您可以更改着色器以允许您选择任何颜色，只需更改行:

if (val.r == 0.0 && val.g == 0.0 && val.b == 0.0) 

到你想要的颜色。 (就像你的情况一样。你可以说 r = 0 g = 1 b = 0 只在绿色上裁剪)

Result of above code on a device

编辑:我想指出减法混合不是必需的，这也可行:

var cropNode = SKCropNode()
var shape = SKShapeNode(rectOf: CGSize(width:100,height:100))
shape.fillColor = SKColor.orange

var shape2 = SKShapeNode(rectOf: CGSize(width:25,height:25))
shape2.fillColor = SKColor.black
shape2.blendMode = .replace
shape.addChild(shape2)

let mask = generateMaskNode(from:shape)

cropNode.addChild(shape)
cropNode.position = CGPoint(x:150,y:170)
cropNode.maskNode=mask
container.addChild(cropNode)

现在我无法测试，这就引出了一个问题，我的功能是否还需要。理论上下面的代码应该可以工作，因为它用上面的代码替换了底层像素，所以理论上 alpha 应该转移过来。如果有人可以对此进行测试，请告诉我它是否有效。

var cropNode = SKCropNode()
var shape = SKShapeNode(rectOf: CGSize(width:100,height:100))
shape.fillColor = SKColor.orange

var shape2 = SKShapeNode(rectOf: CGSize(width:25,height:25))
shape2.fillColor = SKColor(red:0,green:0,blue:0,alpha:0)
shape2.blendMode = .replace
shape.addChild(shape2)

cropNode.addChild(shape)
cropNode.position = CGPoint(x:150,y:170)
cropNode.maskNode= shape.copy() as! SKNode
container.addChild(cropNode)

replace 只替换颜色不替换alpha