Extract preview main pass texture dispatch

docs/modernization/debt.md

@@ -18,6 +18,10 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview::draw_stroke_immediate()`
+  now routes main-pass texture binding through
+  `bind_legacy_node_stroke_preview_main_pass_textures(...)`; the retained path
+  still owns the concrete texture objects and mixer binding callbacks.
 - 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview::draw_stroke_immediate()`
   no longer duplicates main-pass setup in the outer `prepare_main_pass` block;
   the retained main-live-pass helper now owns blend-uniform and texture binding

src/legacy_node_stroke_preview_execution_services.h

@@ -234,6 +234,49 @@ struct LegacyNodeStrokePreviewPassOrchestrationPlan {
     bool background_colorize = false;
 };
 
+struct LegacyNodeStrokePreviewMainPassTextureDispatch {
+    std::function<void(int)> activate_texture_unit;
+    std::function<void()> bind_brush_tip;
+    std::function<void()> bind_stroke_destination;
+    std::function<void()> bind_pattern;
+    std::function<void()> bind_mixer;
+};
+
+[[nodiscard]] inline LegacyNodeStrokePreviewMainPassTextureDispatch make_legacy_node_stroke_preview_main_pass_texture_dispatch(
+    std::function<void(int)> activate_texture_unit,
+    std::function<void()> bind_brush_tip,
+    std::function<void()> bind_stroke_destination,
+    std::function<void()> bind_pattern,
+    std::function<void()> bind_mixer)
+{
+    return LegacyNodeStrokePreviewMainPassTextureDispatch {
+        .activate_texture_unit = std::move(activate_texture_unit),
+        .bind_brush_tip = std::move(bind_brush_tip),
+        .bind_stroke_destination = std::move(bind_stroke_destination),
+        .bind_pattern = std::move(bind_pattern),
+        .bind_mixer = std::move(bind_mixer),
+    };
+}
+
+inline void bind_legacy_node_stroke_preview_main_pass_textures(
+    const LegacyNodeStrokePreviewMainPassTextureDispatch& dispatch,
+    bool copy_stroke_destination,
+    bool uses_mixer)
+{
+    dispatch.activate_texture_unit(0);
+    dispatch.bind_brush_tip();
+    if (copy_stroke_destination) {
+        dispatch.activate_texture_unit(1);
+        dispatch.bind_stroke_destination();
+    }
+    dispatch.activate_texture_unit(2);
+    dispatch.bind_pattern();
+    dispatch.activate_texture_unit(3);
+    if (uses_mixer) {
+        dispatch.bind_mixer();
+    }
+}
+
 template <typename Frame>
 struct LegacyNodeStrokePreviewMainLivePassRequestT {
     std::function<void()> setup_blend_uniforms;

src/node_stroke_preview.cpp

@@ -244,24 +244,29 @@ void bind_stroke_preview_main_pass_textures(
     bool copy_stroke_destination,
     bool uses_mixer)
 {
-    set_active_texture_unit(stroke_preview_live_slots::kTip);
+    pp::panopainter::bind_legacy_node_stroke_preview_main_pass_textures(
-    brush.m_tip_texture ?
+        pp::panopainter::make_legacy_node_stroke_preview_main_pass_texture_dispatch(
-        brush.m_tip_texture->bind() :
+            [&](int texture_slot) {
-        unbind_texture_2d();
+                set_active_texture_unit(texture_slot);
-
+            },
-    if (copy_stroke_destination)
+            [&] {
-    {
+                brush.m_tip_texture ?
-        set_active_texture_unit(stroke_preview_live_slots::kDestination);
+                    brush.m_tip_texture->bind() :
-        stroke_destination_texture.bind();
+                    unbind_texture_2d();
-    }
+            },
-
+            [&] {
-    set_active_texture_unit(stroke_preview_live_slots::kPattern);
+                stroke_destination_texture.bind();
-    brush.m_pattern_texture ?
+            },
-        brush.m_pattern_texture->bind() :
+            [&] {
-        unbind_texture_2d();
+                brush.m_pattern_texture ?
-
+                    brush.m_pattern_texture->bind() :
-    set_active_texture_unit(stroke_preview_live_slots::kMixer);
+                    unbind_texture_2d();
-    uses_mixer ? mixer_rtt.bindTexture() : unbind_texture_2d();
+            },
+            [&] {
+                mixer_rtt.bindTexture();
+            }),
+        copy_stroke_destination,
+        uses_mixer);
 }
 
 void bind_stroke_preview_destination_texture(Texture2D& texture)

tests/paint_renderer/compositor_tests.cpp

@@ -2611,6 +2611,54 @@ void legacy_node_stroke_preview_main_live_pass_preserves_order(pp::tests::Harnes
     PP_EXPECT(h, !invalid);
 }
 
+void legacy_node_stroke_preview_main_pass_texture_dispatch_preserves_order(pp::tests::Harness& h)
+{
+    std::vector<std::string> steps;
+    const auto run = [&](bool copy_stroke_destination, bool uses_mixer) {
+        steps.clear();
+        pp::panopainter::bind_legacy_node_stroke_preview_main_pass_textures(
+            pp::panopainter::make_legacy_node_stroke_preview_main_pass_texture_dispatch(
+                [&](int texture_slot) {
+                    steps.emplace_back("unit:" + std::to_string(texture_slot));
+                },
+                [&] {
+                    steps.emplace_back("bind_tip");
+                },
+                [&] {
+                    steps.emplace_back("bind_destination");
+                },
+                [&] {
+                    steps.emplace_back("bind_pattern");
+                },
+                [&] {
+                    steps.emplace_back("bind_mixer");
+                }),
+            copy_stroke_destination,
+            uses_mixer);
+    };
+
+    run(false, false);
+    PP_EXPECT(h, steps == std::vector<std::string> {
+        "unit:0",
+        "bind_tip",
+        "unit:2",
+        "bind_pattern",
+        "unit:3",
+    });
+
+    run(true, true);
+    PP_EXPECT(h, steps == std::vector<std::string> {
+        "unit:0",
+        "bind_tip",
+        "unit:1",
+        "bind_destination",
+        "unit:2",
+        "bind_pattern",
+        "unit:3",
+        "bind_mixer",
+    });
+}
+
 void legacy_node_stroke_preview_stroke_setup_plan_preserves_curve_and_dual_inputs(pp::tests::Harness& h)
 {
     const auto plan = pp::panopainter::plan_legacy_node_stroke_preview_stroke_setup(
@@ -3204,6 +3252,9 @@ int main()
     harness.run(
         "legacy_node_stroke_preview_main_live_pass_preserves_order",
         legacy_node_stroke_preview_main_live_pass_preserves_order);
+    harness.run(
+        "legacy_node_stroke_preview_main_pass_texture_dispatch_preserves_order",
+        legacy_node_stroke_preview_main_pass_texture_dispatch_preserves_order);
     harness.run(
         "legacy_node_stroke_preview_stroke_setup_plan_preserves_curve_and_dual_inputs",
         legacy_node_stroke_preview_stroke_setup_plan_preserves_curve_and_dual_inputs);