SceneKit - What orthographicProjection to use for

Question

What orthographicProjection does one have to use to be able to make a 2D application in SceneKit with 1:1 SceneKit points to screen points/pixels ratio?

Example: I want to position something at (200, 200) on the screen and I want to use a SCNVector with (200, 200, 0) for it. What orthographicProjection do I need for this?

Answer 1

If you want an orthographic projection where a unit of scene space corresponds to a point of screen space, you need a projection where the left clipping plane is at zero and the right clipping plane is at whatever the screen's width in points is. (Ditto for top/bottom, and near/far doesn't matter so long as you keep objects within whatever near/far you set up.)

For this it's probably easiest to set up your own projection matrix, rather than working out what orthographicScale and camera position correspond to the dimensions you need:

GLKMatrix4 mat = GLKMatrix4MakeOrtho(0, self.view.bounds.size.width,
                                     0, self.view.bounds.size.height,
                                     1, 100); // z range arbitrary
cameraNode.camera.projectionTransform = SCNMatrix4FromGLKMatrix4(mat);
// still need to position the camera for its direction & z range
cameraNode.position = SCNVector3Make(0, 0, 50);