Converting between coordinate spaces SpriteKit

Question

I have a node with the shape of a box in a scene. The shape node should have its own coordinate space, so if I declare a point at (100,100) in the nodes coordinate space and rotate the box pi/4 rad the point should change in the scenes coordinate space.

My problem is I cant get this to work, I'm using the following code to convert a point in the nodes coord space to the scenes coord space, the placement of the node is 200,200 in the scene:

startPointInNodeSpace = CGPointMake(0, size.height/2);
CGPoint start = [self.scene convertPoint:CGPointMake(startPointInNodeSpace.x, startPointInNodeSpace.y) fromNode:self.parent];
CGPoint end = [self.scene convertPoint:CGPointMake(startPointInNodeSpace.x, startPointInNodeSpace.y + 100) fromNode:self.parent];
NSLog(@"start position in node: (%f,%f)\nend position in node: (%f,%f)",startPointInNodeSpace.x,startPointInNodeSpace.y,startPointInNodeSpace.x,startPointInNodeSpace.y + 100);
NSLog(@"start position in scene: (%f,%f)\nend position in scene: (%f,%f)",start.x,start.y,end.x,end.y);

The code is inside a subclass of SKSpriteNode.

My log:

start position in node: (0.000000,20.000000)
end position in node: (0.000000,120.000000)
start position in scene: (0.000000,20.000000)
end position in scene: (0.000000,120.000000)

As you can see it is not converting the points at all but I dont know what I am doing wrong.

Visual Illustration of what I want to achieve:

Conversion

self is the blue box which is a SKSpriteNode with position = 200,200. it is a child of the scene — Marcus, May 29 '14 at 21:03

score 2 · Answer 1 · answered May 29 '14 at 21:10

2

I think the problem is that you're converting from self.parent instead of self — the node's parent is the scene, so there's no conversion to be done. Try converting from self instead:

startPointInNodeSpace = CGPointMake(0, size.height/2);
endPointInNodeSpace = CGPointMake(startPointInNodeSpace.x, startPointInNodeSpace.y + 100);
CGPoint start = [self.scene convertPoint:startPointInNodeSpace fromNode:self];
CGPoint end = [self.scene convertPoint:endPointInNodeSpace fromNode:self];

(Note that you can just pass startPointInNodeSpace into the method, rather than creating an identical point. Structs are copied by value, so the method can't mutate your variable.)

answered May 29 '14 at 21:10

Austin

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then i get: start position in node: (0.000000,20.000000) end position in node: (0.000000,120.000000) start position in scene: (200.000000,220.000000) end position in scene: (200.000000,320.000000) which doesnt seem right either? – Marcus May 29 '14 at 21:25
Sounds like the conversion method doesn't take rotation into account. – Austin May 29 '14 at 21:27
maybe the coord space isnt rotating when the node is? – Marcus May 29 '14 at 21:30

score 0 · Accepted Answer · answered May 29 '14 at 22:37

I was using the following code in the scene to rotate the node:

SKAction *rotation = [SKAction rotateByAngle: M_PI/4.0 duration:0];
[MYNODE runAction: rotation];

When I changed it to this inside the nodeclass instead it worked as expected:

self.zRotation = M_PI/4;

Converting between coordinate spaces SpriteKit

2 Answers2