docs: update ROADMAP for Phase 6 progress

- Marked Phase 6 as IN PROGRESS
- Updated RenderTexture overhaul (#6) as PARTIALLY COMPLETE
- Marked Grid background colors (#50) as COMPLETED
- Added technical notes from implementation experience
- Identified viewport rendering (#8) as next priority

ROADMAP.md

@@ -61,12 +61,17 @@
   - OOP Scene support with lifecycle methods (#61)
   - Window resize events (#1)
   - Scene transitions with animations (#105)
+- 🚧 **Phase 6 Started** - Rendering Revolution in progress!
+  - Grid background colors (#50) ✅
+  - RenderTexture base infrastructure ✅
+  - UIFrame clipping support ✅
 
 ### Active Development:
 - **Branch**: alpha_streamline_2
-- **Current Phase**: Phase 6 - Rendering Revolution (preparing to start)
+- **Current Phase**: Phase 6 - Rendering Revolution (IN PROGRESS)
 - **Timeline**: 3-4 weeks for Phase 6 implementation
 - **Strategic Vision**: See STRATEGIC_VISION.md for platform roadmap
+- **Latest**: RenderTexture base infrastructure complete, UIFrame clipping working!
 
 ### 🏗️ Architectural Dependencies Map
 
@@ -223,27 +228,27 @@ Rendering Layer:
 ```
 *Result*: Entire window/scene system modernized with OOP design!
 
-### Phase 6: Rendering Revolution (3-4 weeks) 🚀 NEXT!
+### Phase 6: Rendering Revolution (3-4 weeks) 🚧 IN PROGRESS!
 **Goal**: Professional rendering capabilities
 ```
-1. #6 - RenderTexture overhaul [CORE PRIORITY]
-   - All UIDrawables render to RenderTexture
-   - Enables clipping to parent bounds
-   - Off-screen rendering for effects
-   - Technical challenges:
-     * Scene transition system now uses RenderTextures
-     * Need to preserve compatibility
-     * Performance implications for nested rendering
+1. ✅ #50 - Grid background colors [COMPLETED]
+   grid.background_color = mcrfpy.Color(50, 50, 50)
+   - Added background_color property with animation support
+   - Default dark gray background (8, 8, 8, 255)
    
-2. #8 - Viewport-based rendering
+2. 🚧 #6 - RenderTexture overhaul [PARTIALLY COMPLETE]
+   ✅ Base infrastructure in UIDrawable
+   ✅ UIFrame clip_children property
+   ✅ Dirty flag optimization system
+   ✅ Nested clipping support
+   ⏳ Extend to other UI classes
+   ⏳ Effects (blur, glow, etc.)
+   
+3. #8 - Viewport-based rendering [NEXT PRIORITY]
    - RenderTexture matches viewport
    - Proper scaling/letterboxing
    - Coordinate system transformations
    
-3. #50 - Grid background colors [QUICK WIN]
-   grid.background_color = mcrfpy.Color(50, 50, 50)
-   grid.background_texture = texture  # stretch/tile options
-   
 4. #106 - Shader support [STRETCH GOAL]
    sprite.shader = mcrfpy.Shader.load("glow.frag")
    frame.shader_params = {"intensity": 0.5}
@@ -257,10 +262,13 @@ Rendering Layer:
 
 **Phase 6 Technical Notes**:
 - RenderTexture is the foundation - everything else depends on it
-- Grid backgrounds (#50) can be done quickly as a warm-up
-- Shader/Particle systems might be deferred to Phase 7 or Gamma
-- Must maintain performance with nested RenderTextures
+- Grid backgrounds (#50) ✅ completed as warm-up task
+- RenderTexture implementation uses opt-in architecture to preserve backward compatibility
+- Dirty flag system crucial for performance - only re-render when properties change
+- Nested clipping works correctly with proper coordinate transformations
 - Scene transitions already use RenderTextures - good integration test
+- Next: Viewport rendering (#8) will build on RenderTexture foundation
+- Shader/Particle systems might be deferred to Phase 7 or Gamma
 
 *Rationale*: This unlocks professional visual effects but is complex.