Blender 2.8 Python Meeting Notes

[xrg]

https://lists.blender.org/pipermail/bf-committers/2018-June/049492.html

Hi, here are meeting notes from the code-quest Python meeting,

Topics mostly covered task:
https://developer.blender.org/T47811

Which proposes changes for 2.8. Rationale for some changes aren’t listed here, see the task for details.

Keyword Only Arguments

For generated RNA API, and by convention in Blender’s API’s any optional keyword arguments are to be keyword only arguments.

• Bastien handles.

Remove ‘register_module’

Scripts must register classes.

• Campbell handles.

Remove ‘addons’ from ‘sys.path’

Allow for package manager to handle many addons w/o polluting module namespace.

• Campbell handles.

Use Python’s @ Matrix Multiply Operator

Meeting agrees to follow Python/NumPy conventions for vector, matrix, quaternion multiplication. However we will need to allow time (some months at least) for addons to be upgraded before adding back ‘*’ as element-wise multiply. Introducing both at once would be very confusing.

• Campbell handles.

Object Selection

Use internal ‘Base’ struct to access selection, the RNA API needs to match logic in C for storage of selection.

• Brecht handles.

Handler ‘bpy.app.handlers.scene_update_pre’

This was being mis-used because of a bug causing it to run constantly.

API’s to replace this can be:

• A timer API to run Python code at less frequent intervals, encourage timers to run less frequently, the timer must be explicitly told to run again each time (avoiding timers being left enabled)

  • Bastien handles.

• Another use case use synchronizing data a depsgraph API needs to handle this.

  • Sergey handles.

f-strings

Replace existing “%” string formatting with f-strings or the format method.

• Campbell handles.

Follow pep8 for Function Calls

For function calls (especially for bpy.props.*) we use 8 spaces, should be 4 (can be mostly auto-formatted).

• Campbell handles.

Type Hints

Encourage use of type hints for complex addon’s.

Use may be investigated for other modules, however we should take care not to add startup overhead unless this gives big benefits.

• Sybren handles.

Drawing API

Drawing (gawain)

Move into gpu module, we can extend as needed.

Keep “bgl” but deprecate it since we can’t ensure OpenGL API’s will be kept longer term, we will try to provide functionality via the GPU module where possible.

• Campbell handles (ongoing development).

Material Import/Export

For import export addons, we would like to read/write basic material options from the node tree (diffuse image, specular color… etc).

• Brecht handles.

Blender/Python API Test Cases

To validate Blender’s Python API is working, we’ve defined a minimum set of addons which should be working before we call others to port scripts.

• Export uv layout.
• Import images as planes.
• Demo Mode.
• BlenderID.
• 3D Print Toolbox.
  
  
  • Bastien, Campbell & Sybren handle.

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- Campbell

[mafster]

awesome

[SynaGl0w]

Nice thread necro… however I see there is a lack of Python API threads related to 2.8 so I’ll comment.

Drawing API

Drawing (gawain)

Move into gpu module, we can extend as needed.

Keep “bgl” but deprecate it since we can’t ensure OpenGL API’s will be kept longer term, we will try to provide functionality via the GPU module where possible.

• Campbell handles (ongoing development).

Is the long term plan is to abstract away OpenGL for just python API? Or is this going to be for an abstraction layer between Blender and OpenGL to more easily facilitate alternatives to OpenGL (Vulcan, DirectX, Metal, etc.) down the road?

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Related to that, are there any plans for an easier way to create/draw custom controls in UILayouts of panels? Right now it is a big pain in the ass with very hacky continuously running “modal” operators for input and bgl for drawing combined with ctypes and as_pointer to do introspection of said layout in order to properly “insert” a custom control. Blender has always seemed very lacking with regard to custom controls/UIs.

A custom control class that handles events and drawing would be welcome. Really rough example:

class Example(CustomControl):
	bl_idname = "EXAMPLE_CT_custom_control"

	#... register, unregister - set/clean up default control state, custom shaders, etc.

	@classmethod
	def poll(cls, context):
		# ... Valid context for custom control? Optional.

	def calc(self, layout_info):
		# ... Return metrics to layout. Optional. For example custom height.

	def input(self, context, event):
		# ... Check input events, tag_redraw() if needed, return state (focus, defocus, etc.)

	def draw(self, context, theme):
		# ... OpenGL drawing, text, easy access to theme colors, etc.

class ExamplePanel(Panel):
	# ...
	def draw(self, context):
		self.layout.custom_control("EXAMPLE_CT_custom_control") # or Example.bl_idname

It would allow addon creators to build cool stuff like custom graph editors, 3D graphs, multi-line text fields, generative operator inputs like shapes or profiles, custom asset fields, custom previews, etc.

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As a side note, I would love to see pillow included with Blender’s default python environment (as numpy has been).