Maya API - Custom Camera Transform nodes raise an error

[david-cattermole]

Problem

mmSolver only works with Maya transform and camera nodes. Sub-classed, custom plug-ins will cause an assertion error (because they are untested).
We should attempt to allow all types of transform nodes, even if they are custom plug-ins.

Expected behavior:
If a camera (transform and shape node) are custom (derived API nodes), then we should not error.

Actual behavior:
When loading 2D Marker data onto a camera with custom Maya transform plugin (MPxTransform), we get an assertion error.

# Traceback (most recent call last):
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/solver/ui/solver_window.py", line 365, in loadMarkerCB
#     loadmarker_tool.open_window()
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/tool.py", line 22, in open_window
#     loadmarker_window.main()
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/ui/loadmarker_window.py", line 121, in main
#     delete=delete
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/ui/base_maya_window.py", line 120, in open_window
#     cls.instance = cls(parent=parent, name=name)
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/ui/loadmarker_window.py", line 38, in __init__
#     self.addSubForm(loadmarker_layout.LoadMarkerLayout)
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/ui/base_maya_window.py", line 79, in addSubForm
#     self.subForm = SubForm(self)
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/ui/loadmarker_layout.py", line 77, in __init__
#     self.populateUi()
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/ui/loadmarker_layout.py", line 85, in populateUi
#     selected_cameras
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/ui/loadmarker_layout.py", line 122, in updateCameraList
#     self.populateCameraModel(model)
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/ui/loadmarker_layout.py", line 136, in populateCameraModel
#     camera_nodes = lib.get_cameras()
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/tools/loadmarker/lib.py", line 83, in get_cameras
#     cam = mmapi.Camera(shape=node)
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/_api/camera.py", line 47, in __init__
#     self.set_shape_node(shape)
#   File "/home/davidc/maya/modules/mayaMatchMoveSolver-0.2.1-maya2018-linux/python/mmSolver/_api/camera.py", line 163, in set_shape_node
#     assert tfm_dag.apiType() == OpenMaya.MFn.kTransform
# AssertionError

Steps to Reproduce

1. Select a custom transform camera node plug-in.
2. Run the Load Markers UI tool.
3. We get an error.

Software Versions

• mmSolver version:
  v0.2.1

• Maya version:
  Maya 2018

• Operating System (OS):
  Linux

[david-cattermole]

I have changed the mmSolver API to allow custom Maya transform node plug-ins, now. Assuming the custom transform node still uses the standard Maya translate, rotate and scale attributes, I expect any Maya transform plug-in node to work with mmSolver.

This will be merged into the master branch as part of #72 and #57.

[david-cattermole]

It has been reported that this issue is happening again, in v0.3.2.

[david-cattermole]

The problem in question seems to be due to type checking against the transform node type explicitly.

For example:

mayaMatchMoveSolver/python/mmSolver/utils/camera.py

Line 51 in acf2d41

elif node_type == 'transform':

To effectively fix the bug, and ensure we don't reintroduce the bug, we need to write unit tests for (all?) tools that work with cameras. We will need to create a test transform plug-in, and load it during the unit tests.

This is a relatively low priority problem, because workflows exist to work around the problem, and the user base affected is small.

[david-cattermole]

Custom transform plug-in nodes will now work for cameras.

All the unit tests seem to work. It's still possible there's some mmSolver.tool.* code that doesn't work, but the utilities and API work correctly with custom transform nodes.

The only requirement of a transform node is that it's derived from a transform. It is not possible to derive a custom MPxNode with the same attributes - it must derive from MPxTransform.