From ac783580224c1040a3e57f961736e9ac5cce1bb9 Mon Sep 17 00:00:00 2001
From: omigamedev <omarator@gmail.com>
Date: Sat, 13 Jun 2026 05:13:18 +0200
Subject: [PATCH] Route stroke preview checkerboard setup through helper

---
 docs/modernization/debt.md    |  5 +++++
 docs/modernization/roadmap.md |  4 ++++
 src/node_stroke_preview.cpp   | 11 +++++++----
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/docs/modernization/debt.md b/docs/modernization/debt.md
index db3e0ee..5d93f0f 100644
--- a/docs/modernization/debt.md
+++ b/docs/modernization/debt.md
@@ -18,6 +18,11 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview` preview
+  background checkerboard shader setup now routes through
+  `legacy_canvas_draw_merge_services.h`, preserving the existing colorize
+  condition and preview MVP. The retained preview path still owns background
+  capture ordering, texture copies, stroke setup, and draw execution.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::draw_merge` non-stroke
   `TextureBlend` shader setup now routes through
   `legacy_canvas_draw_merge_services.h`, preserving the optional `TexBG`
diff --git a/docs/modernization/roadmap.md b/docs/modernization/roadmap.md
index 2fb95ff..e9a5fe5 100644
--- a/docs/modernization/roadmap.md
+++ b/docs/modernization/roadmap.md
@@ -2997,6 +2997,10 @@ Results:
   optional `TexBG` uniform when copy-based blend destination feedback is active.
   Layer traversal, framebuffer copies, sampler/texture binding, and draw
   ordering remain in the legacy Canvas path.
+- `NodeStrokePreview` preview background drawing now shares the retained
+  draw-merge shader setup helper for checkerboard uniforms, preserving its
+  colorize condition and preview MVP while leaving capture ordering, texture
+  copies, stroke setup, and draw execution in the retained preview path.
 - `Canvas::stroke_draw_mix` now shares the retained stroke composite shader
   helper for mixer-pass `CompDraw` setup, while preserving its caller-specific
   texture slot uniforms. Mixer framebuffer/scissor state, sampler and texture
diff --git a/src/node_stroke_preview.cpp b/src/node_stroke_preview.cpp
index fb85a50..4fe0cf6 100644
--- a/src/node_stroke_preview.cpp
+++ b/src/node_stroke_preview.cpp
@@ -6,6 +6,7 @@
 #include "bezier.h"
 #include "canvas.h"
 #include "app.h"
+#include "legacy_canvas_draw_merge_services.h"
 #include "legacy_canvas_stroke_composite_services.h"
 #include "legacy_canvas_stroke_execution_services.h"
 #include "legacy_canvas_stroke_preview_services.h"
@@ -517,10 +518,12 @@ void NodeStrokePreview::draw_stroke_immediate()
     pp::panopainter::execute_legacy_stroke_preview_background_capture(
         [&] {
             // copy background color to tex2
-            ShaderManager::use(kShader::Checkerboard);
-            ShaderManager::u_int(kShaderUniform::Colorize, b->m_tip_mix > 0.f || b->m_blend_mode != 0);
-            float aspect = size.x / size.y;
-            ShaderManager::u_mat4(kShaderUniform::MVP, glm::ortho(-.5f, .5f, -.5f / aspect, .5f / aspect, -1.f, 1.f));
+            const float aspect = size.x / size.y;
+            pp::panopainter::setup_legacy_canvas_draw_merge_checkerboard_shader(
+                pp::panopainter::LegacyCanvasDrawMergeCheckerboardUniforms {
+                    .mvp = glm::ortho(-.5f, .5f, -.5f / aspect, .5f / aspect, -1.f, 1.f),
+                    .colorize = b->m_tip_mix > 0.f || b->m_blend_mode != 0,
+                });
         },
         [&] {
             m_plane.draw_fill();