CODEWITHSUNDEEP
iossprite-kitskphysicsbodyskphysicsjoint
BGreenstone
BGreenstone

Reputation: 360

Can SKPhysicsJoints be used in a scrolling SpriteKit game?

This seems to be a major oversight by Apple, but since SKPhysicsJoints have their anchor points set in Scene coordinates, this makes doing any kind of scrolling game impossible.

To simulate a camera in SpriteKit you create a WorldNode which contains all of the gameplay elements, and then pan that around the scene. Unfortunately, doing this causes the Scene coordinates of every object in the game to change on every frame as you pan the world around. In turn, this breaks the joint anchor points, and things go berserk.

There isn't even a way to change the joint's anchor point, so I don't even have a way of just updating the coordinate every frame. It would seem that using SKPhysicsJoint in a scrolling game is not an option.

Does anyone know of a way around this?

Upvotes: 3

Views: 290

Answers (1)

BGreenstone
BGreenstone

Reputation: 360

Ok, I think I figured out what was going on, and I was totally incorrect in my original assumption. The reason my anchor points looked incorrect is because the [convertPoint toNode] call was returning me Scene coordinates that were incorrect. After several hours I realized it was off by exactly half the screen dimensions. My Scene has an anchorPoint of (0.5, 0.5), but this screws up the conversion values. So, if I simply offset the point by width/2, height/2 it's correct:

GPoint pt = CGPointMake(anchorWorldX, anchorWorldY);
pt = [gGameScene convertPoint:pt fromNode:gGameWorld]; // convert to scene coords, but it's WRONG

pt.x += scene.size.width * scene.anchorPoint.x;   // this properly adjusts the value to be correct
pt.y += scene.size.height * scene.anchorPoint.y;

SKPhysicsJointPin* pin =[SKPhysicsJointPin jointWithBodyA:hinge.physicsBody bodyB:door.physicsBody anchor:pt];

Upvotes: 3

Related Questions