如何從SKSpriteNode或SKTexture獲取像素顏色？

Question

我想在遊戲地圖上精確選擇我的對象。對象是一個精靈，它周圍有一些透明的像素，我想測試這些透明像素的觸摸位置。 任何線索？

Answer 1

在Sprite Kit中，您無權訪問紋理數據。

相反，您必須從圖像創建一個位掩碼，例如通過將圖像加載爲UIImage或CGImage並掃描所有非透明像素。

Answer 2

您可以繼承SKSpriteNode的子類，在檢測觸摸時添加對圖像的引用並檢查該圖像的alpha。

1）添加一個實例變量來保存你的形象

@implementation DraggableSprite { 
    UIImage *_holdingImage; 
} 

2）然後在init方法可以保存參考該圖像

-(id)initWithImageNamed:(NSString *)name { 
    if (self=[super initWithImageNamed:name]) { 

     self.userInteractionEnabled = YES;//enable touches handling 
     self.anchorPoint = P(0,0); 
     _holdingImage = [UIImage imageNamed:name]; 
    } 
    return self; 
} 

3）檢測的觸摸

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { 
    UITouch *touch = [touches anyObject]; 
    CGPoint positionInScene = [touch locationInNode:self]; 

    CGFloat a = [UIImage getAlphaFromImage:_holdingImage atX:positionInScene.x andY:self.size.height-positionInScene.y]; 
    NSLog(@"alpha is %f",a); 
} 

4）阿爾法檢查功能

+(CGFloat)getAlphaFromImage:(UIImage*)image atX:(NSInteger)xx andY:(NSInteger)yy { 
    // Cancel if point is outside image coordinates 
    if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), CGPointMake(xx,yy))) { 
     return 0; 
    } 

    // Create a 1x1 pixel byte array and bitmap context to draw the pixel into. 
    // Reference: http://stackoverflow.com/questions/1042830/retrieving-a-pixel-alpha-value-for-a-uiimage 
    NSInteger pointX = xx; 
    NSInteger pointY = yy; 
    CGImageRef cgImage = image.CGImage; 
    NSUInteger width = image.size.width; 
    NSUInteger height = image.size.height; 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    int bytesPerPixel = 4; 
    int bytesPerRow = bytesPerPixel * 1; 
    NSUInteger bitsPerComponent = 8; 
    unsigned char pixelData[4] = { 0, 0, 0, 0 }; 
    CGContextRef context = CGBitmapContextCreate(pixelData, 
               1, 
               1, 
               bitsPerComponent, 
               bytesPerRow, 
               colorSpace, 
               kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); 
    CGColorSpaceRelease(colorSpace); 
    CGContextSetBlendMode(context, kCGBlendModeCopy); 

    // Draw the pixel we are interested in onto the bitmap context 
    CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height); 
    CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage); 
    CGContextRelease(context); 

    CGFloat alpha = (CGFloat)pixelData[3]/255.0f; 
    return alpha; 
} 

Answer 3

這裏是如何直接從SKTexture得到一個像素的顏色：

class SpriteKitUtility 
{ 
    class func pixelFromTexture(texture: SKTexture, position: CGPoint) -> SKColor { 
     let view = SKView(frame: CGRectMake(0, 0, 1, 1)) 
     let scene = SKScene(size: CGSize(width: 1, height: 1)) 
     let sprite = SKSpriteNode(texture: texture) 
     sprite.anchorPoint = CGPointZero 
     sprite.position = CGPoint(x: -floor(position.x), y: -floor(position.y)) 
     scene.anchorPoint = CGPointZero 
     scene.addChild(sprite) 
     view.presentScene(scene) 
     var pixel: [Byte] = [0, 0, 0, 0] 
     let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue) 
     let context = CGBitmapContextCreate(&pixel, 1, 1, 8, 4, CGColorSpaceCreateDeviceRGB(), bitmapInfo); 
     UIGraphicsPushContext(context); 
     view.drawViewHierarchyInRect(view.bounds, afterScreenUpdates: true) 
     UIGraphicsPopContext() 
     return SKColor(red: CGFloat(pixel[0])/255.0, green: CGFloat(pixel[1])/255.0, blue: CGFloat(pixel[2])/255.0, alpha: CGFloat(pixel[3])/255.0) 
    } 
}