[Tracking] PME2: GPU Layout System - Interactive UI Framework

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Overview

Build a complete GPU-based UI layout system that mirrors Blender's UILayout API, enabling rich interactive panels, menus, and tooltips rendered via GPU.

This system provides:

• Declarative API similar to bpy.types.UILayout
• Interactive widgets (buttons, props, sliders)
• Hit testing for mouse interaction
• Theme integration with Blender's UI themes

Related Issues

• PME2: GPU-rendered description tooltip for Pie Menu #100 - GPU-rendered description tooltip (original feature request)
• PME2: description / description_expr implementation #81 - description/description_expr implementation

Architecture

ui/gpu/
├── __init__.py      # Public exports
├── style.py         # GPULayoutStyle, theme integration
├── drawing.py       # GPUDrawing, BLFDrawing, IconDrawing
├── items.py         # LayoutItem, LabelItem, ButtonItem, etc.
├── layout.py        # GPULayout (main API)
├── tooltip.py       # GPUTooltip
├── interactive.py   # HitRect, HitTestManager, InteractionState
└── test_layout.py   # Test operators

Sub-issues (Phases)

Phase A: Foundation

• GPU Layout: Multi-area rendering with region targeting #105 - Multi-area rendering (region targeting) ✅
• GPU Layout: UI scaling with over_scale pattern #106 - UI scaling (over_scale pattern)

Phase B: Interaction

• GPU Layout: Panel drag and close button #107 - Panel drag & close button ✅
• GPU Layout: Panel resize and position persistence #108 - Panel resize & position persistence

Phase C: Visual Quality

• GPU Layout: Text rendering improvements #109 - Text rendering improvements (shadow, clipping, ellipsis)
• GPU Layout: Complete theme integration #110 - Complete theme integration

Future: Widgets

• layout.prop() implementation (slider, checkbox, enum)
• layout.template_*() methods

Completed

• Basic GPULayout with label(), separator(), row(), column()
• ButtonItem with hover/press states
• HitTestManager for mouse interaction
• GPULayoutStyle.from_blender_theme()
• GPUTooltip for structured tooltips
• Region targeting - Draw only in invoking region (commit 160e33e)
• Panel drag & close - Title bar with platform-aware close button (commit 4389902)

Design Principles

1. UILayout-compatible API: layout.label(), layout.operator(), layout.prop()
2. Automatic HitRect registration: Interactive items auto-register with HitTestManager
3. Theme-aware: Colors from Blender theme, respects ui_scale
4. Region-scoped: Draw only in the invoking region, not all regions of same type

Key Patterns Discovered

Position State Management (from #107)

When UI is rebuilt each frame, externalize mutable state to the operator:

# Store position in operator
self._panel_x = self._layout.x
self._panel_y = self._layout.y
# Use stored position on rebuild
layout = GPULayout(x=self._panel_x, y=self._panel_y, ...)

References

• bl_ui_widgets (GPL-3.0): https://github.com/mmmrqs/bl_ui_widgets

Notes

• Tooltip via GPU is now optional since PME2: Macro operator improvements - description and argument-free invocation #102 found dynamic bl_description method
• Focus is on building a complete UI framework, not just tooltips