iOS 9 更新后 SKFieldNode 定位错误

SKFieldNode positioned wrong after iOS 9 update

我有一些代码在 iOS 8 中工作得很好,但是自从 iOS 9 以来,一些 SKFieldNodes 的行为非常奇怪。下图显示了一个场景,其中有两个 SKFieldNodes(标有红色精灵)和一个 SKEmitterNode 发射金色粒子。

在 iOS 8 中,磁场会吸引粒子并 "suck" 它们朝向磁铁的尖端。由于 iOS 9,粒子向右上角加速,如红色箭头所示。此外,我还必须增加字段的 strength 才能使效果可见。

对应代码如下:

            SKSpriteNode* magnet = [SKSpriteNode spriteNodeWithImageNamed:@"StarMagnet_main"];

            //Add field node
            SKFieldNode* field = [SKFieldNode radialGravityField];
            field.strength = 10.0;
            field.falloff = 0.1;

            //Add a red circle to visualize the node
            SKShapeNode* debugNode = [SKShapeNode shapeNodeWithCircleOfRadius:20.0];
            debugNode.fillColor = [UIColor redColor];
            [field addChild:debugNode];

            field.position = CGPointMake(magnet.size.width * 0.3, magnet.size.height * 0.45);

            field.categoryBitMask = LECategoryDust;
            [magnet addChild:field];

            //Add second field
            field = [field copy];
            field.position = CGPointMake(-field.position.x, field.position.y);
            [magnet addChild:field];

            //Add particle emitter
            SKEmitterNode* emitter = [SKEmitterNode emitterNamed:@"MagneticParticleEmitter"];
            emitter.fieldBitMask = LECategoryDust;
            emitter.position = CGPointMake(0, magnet.size.height/2.0);
            [magnet addChild:emitter];

好像字段节点位于右上角附近的某个地方,但是红色圆圈子节点显示不同。

仔细调查后,我断定这是一个 SpriteKit 错误引入 iOS 9. 下面你可以找到一个由 SKEmitterNode, SKFieldNode 组成的测试场景和两个 SKShapeNodes 标记初始视口和字段的位置。所有节点都是用于翻译“世界”的 rootNode 的后代。

虽然场的位置没有改变,但它的效果中心会改变。

仅当 SKEmitterNode's targetNode 属性 设置为 scene 时力计算才是正确的,这并不总是需要的。

黄色圆圈标记了字段的位置。然而,粒子被吸引到右上角。以下是此时的一些位置:

Root scene pos: 160x, 284y | parent pos: 160x, 284y
Field scene pos: 80x, 142y | parent pos: -80x, -142y
Target scene pos: 80x, 142y | parent pos: -80x, -142y

如您所见,该字段和黄色圆圈具有相同的位置(和父级)。

移动场景时(即仅rootNode),粒子被拉向另一个点,该点移动到更靠近左下角的位置,同时平移到相反的位置。

翻译后的一些位置:

Root scene pos: 84x, 149y | parent pos: 84x, 149y
Field scene pos: 4x, 7y | parent pos: -80x, -142y
Target scene pos: 4x, 7y | parent pos: -80x, -142y

场地位置没变,重心变了

视频

为了更好地说明该行为,我上传了截屏视频: https://youtu.be/EJs4vPYMndU

代码

欢迎大家自行尝试,下面是本次实验使用的测试场景代码:

#import "LEDebugScene.h"
#import "LEPhysicsCategories.h"
    
@implementation LEDebugScene

SKNode* rootNode;
SKFieldNode* fieldNode;
SKShapeNode* targetPosShape;

- (void) didMoveToView:(SKView *)view {
    self.backgroundColor = [SKColor blackColor];
    
    // This will be the desired field's position (in parent space)
    CGPoint fieldPosition = CGPointMake(-self.size.width * 0.25, -self.size.height * 0.25);
    
    // 1. Set up a root node to move around to translate the "world"
    rootNode = [SKNode node];
    rootNode.position = CGPointMake(self.size.width/2.0, self.size.height/2.0);
    [self addChild:rootNode];
    
    // 2. Mark the target position of the field with a circle
    targetPosShape = [SKShapeNode shapeNodeWithCircleOfRadius:20.0];
    targetPosShape.fillColor = [UIColor yellowColor];
    targetPosShape.strokeColor = [UIColor brownColor];
    [rootNode addChild:targetPosShape];
    targetPosShape.position = fieldPosition;
    
    // 3. Mark the initially visible portion of the scene
    SKShapeNode* initialViewportShape = [SKShapeNode shapeNodeWithRect: CGRectMake(-self.size.width/2.0,
                                                                        -self.size.height/2.0,
                                                                        self.size.width,
                                                                        self.size.height)];
    initialViewportShape.fillColor = [UIColor clearColor];
    initialViewportShape.strokeColor = [UIColor redColor];
    initialViewportShape.lineWidth = 3.0;
    [rootNode addChild:initialViewportShape];
    
    // 4. Add an emitter at the center of the initial viewport
    NSString* emitterPath = [[NSBundle mainBundle] pathForResource:@"DebugEmitter" ofType:@"sks"];
    SKEmitterNode* emitterNode = [NSKeyedUnarchiver unarchiveObjectWithFile:emitterPath];
    emitterNode.fieldBitMask = LECategoryDust;
    emitterNode.particlePositionRange = CGVectorMake(self.size.width, self.size.height);
    emitterNode.position = CGPointZero;
    [rootNode addChild:emitterNode];
    
    // 5. Create a field at the desired position
    fieldNode = [SKFieldNode radialGravityField];
    fieldNode.userData = [NSMutableDictionary dictionary];
    fieldNode.categoryBitMask = LECategoryDust;
    fieldNode.falloff = 1.8;
    fieldNode.minimumRadius = 20.0;
    fieldNode.strength = 2.5;
    fieldNode.position = fieldPosition;
    [rootNode addChild:fieldNode];
}

- (void) touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    
    //Get the touch movement vector
    UITouch* touch = [touches anyObject];
    CGPoint prevLoc = [touch previousLocationInNode:self];
    CGPoint location = [touch locationInNode:self];
    CGVector delta = CGVectorMake(location.x - prevLoc.x, location.y - prevLoc.y);
    
    //Translate the world by repositioning the root node
    rootNode.position = CGPointMake(rootNode.position.x + delta.dx, rootNode.position.y + delta.dy);
    
    CGPoint rootScenePos = [self convertPoint:rootNode.position fromNode:rootNode.parent];
    CGPoint fieldScenePos = [self convertPoint:fieldNode.position fromNode:fieldNode.parent];
    CGPoint targetShapeScenePos = [self convertPoint:targetPosShape.position fromNode:targetPosShape.parent];

    NSLog(@"");
    NSLog(@"Root scene pos: %.0fx, %.0fy | parent pos: %.0fx, %.0fy",
          rootScenePos.x, rootScenePos.y, rootNode.position.x, rootNode.position.y);
    NSLog(@"Field scene pos: %.0fx, %.0fy | parent pos: %.0fx, %.0fy",
          fieldScenePos.x, fieldScenePos.y, fieldNode.position.x, fieldNode.position.y);
    NSLog(@"Target scene pos: %.0fx, %.0fy | parent pos: %.0fx, %.0fy",
          targetShapeScenePos.x, targetShapeScenePos.y, targetPosShape.position.x, targetPosShape.position.y);
}

@end

尽管尝试了几个小时,我还是没能通过重新定位字段节点来弥补计算错误。如果有人做了,如果他们能分享它就太好了。

编辑:我还提交了错误报告 (23063175)。