Get View Direction Relative To Scene In Vispy?

What is the cleanest way to get the view direction relative to your scene in vispy? view.scene.transform contains a whole chain of transforms: In [88]: view.scene.transform Out[88]

Solution 1:

Vispy transformations have a map and imap function you can use to map coordinates between scene and screen coordinates in either direction. I used them on points and threw in a lot of assertions to be safe; there are probably simpler implementations. I tested this for orthographic projection. I ~think it will work for perspective projections too as long as the center of projection is in the middle of the screen.

def get_view_direction_in_scene_coordinates(view):
    import numpy
    tform=view.scene.transform
    w,h = view.canvas.size
    screen_center = numpy.array([w/2,h/2,0,1]) # in homogeneous screen coordinates
    d1 = numpy.array([0,0,1,0]) # in homogeneous screen coordinates
    point_in_front_of_screen_center = screen_center + d1 # in homogeneous screen coordinates
    p1 = tform.imap(point_in_front_of_screen_center) # in homogeneous scene coordinates
    p0 = tform.imap(screen_center) # in homogeneous screen coordinates
    assert(abs(p1[3]-1.0) < 1e-5) # normalization necessary before subtraction
    assert(abs(p0[3]-1.0) < 1e-5)
    d2 = p1 - p0 # in homogeneous screen coordinates
    assert(abs(d2[3])< 1e-5)
    d3 = d2[0:3] # in 3D screen coordinates
    d4 = d3 / numpy.linalg.norm(d3)
    return d4