SpriteKit physicsBody for a line - xcode

Question

I am developing a game with SpriteKit. In my game, the player should be able to draw a line and have things interact with it. I'm using a simple SKShapeNode drawn with a CGMutablePathRef. However when I add the physicsBody to the line, it automatically reconnects the end of the line to the start. The result is if the user draws a curve, the physicsBody is the shape of a semicircle.
- (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];
}
I can't seem to figure out how to prevent the physicsBody path from rejoining back to the beginning. Any help would be appreciated. Thanks!

Answer 1

The following code draws a temporary line (white) as you move your finger around the screen and then draws a final line (red) when you lift your finger. The code then adds a edge chain physics body to the line.
#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