Spritekit - Using gestures to draw multiple lines with multiple fingers simultaneously - ios

Question

Using the below code, I can draw a line using the pan gesture using 1 finger. However what I am attempting to do is for 1 finger to draw 1 line and another finger to draw the second simultaneously. I've read somewhere about using a dictionary to store the touches but don't know how to write it in code. Can any one help?
-(void)didMoveToView:(SKView *)view {
UIPanGestureRecognizer *gestureRecognizerPan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:#selector(handlePanFrom:)];
[[self view] addGestureRecognizer:gestureRecognizerPan];
}
- (void)handlePanFrom:(UIPanGestureRecognizer *)recognizer
{
if (recognizer.state == UIGestureRecognizerStateBegan) {
CGPoint touchLocation = [recognizer locationInView:recognizer.view];
touchLocation = [self convertPointFromView:touchLocation];
pathToDraw = CGPathCreateMutable();
CGPathMoveToPoint(pathToDraw, NULL, touchLocation.x, touchLocation.y);
lineNode = [[SKShapeNode alloc] init];
lineNode.path = pathToDraw;
lineNode.name = lineNodeCategoryName;
[_gameLineNode addChild:lineNode];
} else if (recognizer.state == UIGestureRecognizerStateChanged) {
CGPoint touchLocation = [recognizer locationInView:recognizer.view];
touchLocation = [self convertPointFromView:touchLocation];
CGPathAddLineToPoint(pathToDraw, NULL, touchLocation.x, touchLocation.y);
lineNode.path = pathToDraw;
lineNode.name = lineNodeCategoryName;
lineNode.physicsBody = [SKPhysicsBody bodyWithEdgeChainFromPath:pathToDraw];
lineNode.physicsBody.dynamic = YES;
lineNode.strokeColor = [SKColor blackColor];
lineNode.glowWidth = 3.0;
} else if (recognizer.state == UIGestureRecognizerStateEnded) {
CGPathRelease(pathToDraw);
}
}

Answer 1

Drawing multiple lines simultaneously is fairly straightforward. The key is to track each touch event independently. One way to do that is to maintain a dictionary that uses the touch event as the key and the shape node (used to draw the line) as the value.
#implementation GameScene {
NSMutableDictionary *lines;
}
-(void)didMoveToView:(SKView *)view {
self.scaleMode = SKSceneScaleModeResizeFill;
// Create a mutable dictionary
lines = [NSMutableDictionary dictionaryWithCapacity:10];
}
// Add each line node to the dictionary with the touch event as the key
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
for (UITouch *touch in touches) {
CGPoint location = [touch locationInNode:self];
// Create a mutable path
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:location];
// Create a shape node using the path
SKShapeNode *lineNode = [SKShapeNode shapeNodeWithPath:path.CGPath];
lineNode.strokeColor = [SKColor blackColor];
[self addChild:lineNode];
// Use touch pointer as the dictionary key. Since the dictionary key must conform to
// NSCopying, box the touch pointer in an NSValue
NSValue *key = [NSValue valueWithPointer:(void *)touch];
[lines setObject:lineNode forKey:key];
}
}
// Update the lines as needed
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
for (UITouch *touch in touches) {
CGPoint location = [touch locationInNode:self];
// Retrieve the shape node that corresponds to touch
NSValue *key = [NSValue valueWithPointer:(void *)touch];
SKShapeNode *lineNode = [lines objectForKey:key];
if (lineNode != NULL) {
// Create and initialize a mutable path with the lineNode's current path
UIBezierPath *path = [UIBezierPath bezierPathWithCGPath:lineNode.path];
// Add a line to the current touch point
[path addLineToPoint:location];
// Update lineNode
lineNode.path = path.CGPath;
}
}
}
// Remove the line nodes from the dictionary when the touch ends
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
for (UITouch *touch in touches) {
NSValue *key = [NSValue valueWithPointer:(void *)touch];
[lines removeObjectForKey:key];
}
}
#end