PME Treasure

Make a PME action button reflect a Blender property's current state

3 min read

Outcome

Draw a Cursor pivot action that looks pressed whenever Blender’s current pivot is already Cursor:

ts = C.scene.tool_settings; operator(L, "wm.context_set_enum", text="Cursor", depress=ts.transform_pivot_point == "CURSOR", data_path="scene.tool_settings.transform_pivot_point", value="CURSOR")

The state check runs while PME draws the menu. Blender’s public wm.context_set_enum operator runs only after the user clicks the button.

Build the button from one source of truth

  1. Identify the Blender property that owns the real state. Here it is C.scene.tool_settings.transform_pivot_point.
  2. Add a Custom item to the PME menu.
  3. Read the property once for the visible state.
  4. Pass a Boolean comparison to depress=.
  5. Make the deferred operator change that same property.

The important contract is that display and action agree:

pressed state reads property A
click action writes property A

If the button reads one property but changes another, it can look active while its intended action is not.

Show a different label or icon by state

The same Custom item can derive its presentation without performing the action:

ts = C.scene.tool_settings; is_cursor = ts.transform_pivot_point == "CURSOR"; operator(L, "wm.context_set_enum", text="Cursor Active" if is_cursor else "Use Cursor", icon="PIVOT_CURSOR", depress=is_cursor, data_path="scene.tool_settings.transform_pivot_point", value="CURSOR")

Keep the label change modest. A stable noun plus a clear state is easier to scan than a button whose identity changes completely.

Prefer the native control when it is enough

If the goal is simply to expose Blender’s enum, a native property control is shorter and carries Blender’s standard behavior:

L.prop(C.scene.tool_settings, "transform_pivot_point", text="Pivot")

For one native enum choice:

L.prop_enum(C.scene.tool_settings, "transform_pivot_point", "CURSOR", text="Cursor")

Use the state-aware operator button when you need custom action semantics, a deliberate icon, a custom label, or visible pressed-state feedback beyond the native control.

Pitfalls

  • A Custom item is redrawn repeatedly. Read state while drawing, and assign scene data only when the operator runs.
  • depress= changes presentation, not availability. Use row.enabled or a Poll method when the action must be unavailable.
  • Editor-specific state such as C.space_data.shading is valid only in the matching Blender editor.
  • The button should use the current RNA owner. Old copied paths can stay syntactically valid while pointing at obsolete state.
  • Put long workflows in a Macro or a trusted external script and keep the layout expression readable.

This PME 2.1 example uses C, L, and the public wm.context_set_enum operator. It avoids the internal legacy pme.exec convenience operator.

Sources

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