SpriteKit physicsBody for a line

Question

我正在使用SpriteKit开发游戏。在我的游戏中，玩家应该能够绘制一条线并让它与之相互作用。我使用了SKShapeNode绘制的简单CGMutablePathRef。但是当我将physicsBody添加到该行时，它会自动将该行的末尾重新连接到开头。结果是，如果用户绘制曲线，则physicsBody是半圆形。

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    for (UITouch *touch in touches) {
        CGPoint location = [touch locationInNode:self];
        SKShapeNode *line = [SKShapeNode node];
        CGMutablePathRef pathToDraw = CGPathCreateMutable();
        CGPathMoveToPoint(pathToDraw, NULL, location.x, location.y);
        line.path = pathToDraw;
        [line setStrokeColor:[UIColor redColor]];
        [line setLineWidth:5];
        [line setLineCap:kCGLineCapRound];
        [line setLineJoin:kCGLineJoinRound];
        line.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:pathToDraw];
        line.physicsBody.dynamic = NO;
        line.physicsBody.restitution = 1;
        line.name = @"line";
        [self addChild:line];
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    SKShapeNode *oldLine = (SKShapeNode *)[self childNodeWithName:@"line"];
    CGMutablePathRef pathToDraw = (CGMutablePathRef)oldLine.path;
    CGPathAddLineToPoint(pathToDraw, NULL, location.x, location.y);
    [self enumerateChildNodesWithName:@"line" usingBlock:^(SKNode *node, BOOL *stop) {
        [node removeFromParent];
    }];

    SKShapeNode *line = [SKShapeNode node];
    line.path = pathToDraw;
    [line setStrokeColor:[UIColor redColor]];
    [line setLineWidth:5];
    [line setLineCap:kCGLineCapRound];
    [line setLineJoin:kCGLineJoinRound];
    line.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:pathToDraw];
    line.physicsBody.dynamic = NO;
    line.physicsBody.restitution = 1;
    line.name = @"line";
    [self addChild:line];
}

我似乎无法弄清楚如何防止physicsBody路径重新回到开头。任何帮助，将不胜感激。谢谢！

Answer 1

当您在屏幕上移动手指时，以下代码会绘制一条临时线（白色），然后在抬起手指时绘制最后一条线（红色）。然后代码将边缘链物理主体添加到该行。

@implementation GameScene {
    SKShapeNode *lineNode;
    CGPoint startingPoint;
}

-(void)didMoveToView:(SKView *)view {
    self.scaleMode = SKSceneScaleModeResizeFill;
}

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

    startingPoint = positionInScene;
}

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

    // Remove temporary line if it exist
    [lineNode removeFromParent];

    CGMutablePathRef pathToDraw = CGPathCreateMutable();
    CGPathMoveToPoint(pathToDraw, NULL, startingPoint.x, startingPoint.y);
    CGPathAddLineToPoint(pathToDraw, NULL, positionInScene.x, positionInScene.y);

    lineNode = [SKShapeNode node];
    lineNode.path = pathToDraw;
    lineNode.strokeColor = [SKColor whiteColor];
    lineNode.lineWidth = 1;
    [self addChild:lineNode];
}

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

    // Remove temporary line
    [lineNode removeFromParent];

    CGMutablePathRef pathToDraw = CGPathCreateMutable();
    CGPathMoveToPoint(pathToDraw, NULL, startingPoint.x, startingPoint.y);
    CGPathAddLineToPoint(pathToDraw, NULL, positionInScene.x, positionInScene.y);

    SKShapeNode *finalLineNode = [SKShapeNode node];
    finalLineNode.path = pathToDraw;
    finalLineNode.strokeColor = [SKColor redColor];
    finalLineNode.lineWidth = 1;

    finalLineNode.physicsBody = [SKPhysicsBody bodyWithEdgeChainFromPath:pathToDraw];
    [self addChild:finalLineNode];
}

@end