How to change camera type to Orthographic in Sceneform Android SDK?

Question

I'd like to use an Orthographic camera when presenting a model in SceneView (without AR). Couldn't find a way to do so in API. Am I missing something or the feature is missing?

Skyline

Answer 1

ARCore and Sceneform

As far as I know, there's no native ORTHO method (cube frustum) for camera projection in ARCore / Sceneform at the moment. But you can make it manually using 4x4 Matrix. So, all you need to do is to calculate left, right, top, bottom, near and far properties using the following principles.

Here is how your projection matrix 4x4 must look like:

Edit: working code where scaleFactor is a value around 1.3 and height/width are properties of the SceneView.

private fun buildOrthographicMatrix(right: Float,  top: Float, 
                                      far: Float, near: Float): FloatArray {
   val matrix = FloatArray(16)

   matrix[0] = 1 / right
   matrix[1] = 0f
   matrix[2] = 0f
   matrix[3] = 0f

   matrix[4] = 0f
   matrix[5] = 1 / top
   matrix[6] = 0f
   matrix[7] = 0f

   matrix[8] = 0f
   matrix[9] = 0f
   matrix[10] = -2 / (far - near)
   matrix[11] = 0f

   matrix[12] = 0f
   matrix[13] = 0f
   matrix[14] = -(far + near) / (far - near)
   matrix[15] = 1f

   return matrix
}

val newMatrix = buildOrthographicMatrix(1f / scaleFactor, 
                                        1f / scaleFactor * height / width, 
                                        30f, 
                                        0.01f)

camera.projectionMatrix = Matrix(newMatrix)

Aleen

Thanks. What is scaleFactor? How do you calculate it? If sceneView is full screen, width and height equal to screen dimensions? What is the influence of far and near parameters on the result of the projection? If I want a pseudo perfect ortho projection, should I set near to 0 and far to a very big value? Thanks. – Mammoth

Please, read these three posts: forum.unity.com/threads/… and en.wikipedia.org/wiki/3D_projection and gamedev.stackexchange.com/questions/64423/… – Aleen