Share retained stroke preview binding helpers

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` live-pass
+  sampler binding, dual/main pass texture binding, checkerboard/background
+  capture wrapping, and final preview copy-back now route through shared local
+  helpers; mixer state execution and per-sample GL ordering remain retained in
+  the preview node.
 - 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview` dual-pass and
   main-pass frame-loop execution plus full-frame copy-back now route through
   shared local helpers; checkerboard/background capture ordering, texture-unit

docs/modernization/roadmap.md

@@ -3107,6 +3107,10 @@ Results:
   full-frame copy-back now share one local retained helper surface, while
   checkerboard/background capture ordering, texture-unit binding, mixer
   ownership, and final composite semantics remain in the preview node.
+- `NodeStrokePreview` live-pass sampler binding, dual/main pass texture
+  binding, checkerboard/background capture wrapping, and final preview
+  copy-back now share named local helpers, while mixer state execution and
+  per-sample GL ordering remain in the preview node.
 - `Canvas::stroke_draw` pad-pass destination bind/copy/unbind ordering now
   shares the retained stroke execution helper callback surface, while shader
   setup, pad color selection, framebuffer ownership, and final OpenGL draw

docs/modernization/tasks.md

@@ -509,6 +509,13 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `NodeStrokePreview::draw_stroke_immediate()` live-pass sampler
+  binding, dual/main pass texture binding, checkerboard/background capture
+  wrapping, and final preview copy-back now route through named local helpers;
+  mixer state execution and per-sample GL ordering remain local to the preview
+  node. Next slice should target the remaining mixer-pass state/copy ordering
+  or sample-pass destination callback wrapping without reopening the landed
+  preview live-pass or final-composite helpers.
 - 2026-06-13: `NodeStrokePreview::draw_stroke_immediate()` dual-pass and
   main-pass frame-loop execution plus full-frame copy-back now route through
   shared local helpers; checkerboard/background capture ordering, texture-unit

src/node_stroke_preview.cpp

@@ -103,6 +103,14 @@ constexpr std::uint32_t kDual = 3U;
 constexpr std::uint32_t kPattern = 4U;
 }
 
+namespace stroke_preview_live_slots {
+constexpr std::uint32_t kTip = 0U;
+constexpr std::uint32_t kDestination = 1U;
+constexpr std::uint32_t kPattern = 2U;
+constexpr std::uint32_t kMixer = 3U;
+constexpr std::uint32_t kReservedLinear = 4U;
+}
+
 struct StrokePreviewCompositePassInputs {
     glm::vec2 resolution;
     glm::vec2 pattern_scale;
@@ -203,6 +211,110 @@ void copy_stroke_preview_framebuffer_to_texture(
         static_cast<int>(size.y));
 }
 
+void bind_stroke_preview_live_samplers(
+    Sampler& mipmap_sampler,
+    Sampler& linear_sampler,
+    Sampler& repeat_sampler)
+{
+    mipmap_sampler.bind(stroke_preview_live_slots::kTip);
+    linear_sampler.bind(stroke_preview_live_slots::kDestination);
+    repeat_sampler.bind(stroke_preview_live_slots::kPattern);
+    linear_sampler.bind(stroke_preview_live_slots::kMixer);
+    linear_sampler.bind(stroke_preview_live_slots::kReservedLinear);
+}
+
+void bind_stroke_preview_dual_pass_textures(const Brush& dual_brush)
+{
+    set_active_texture_unit(stroke_preview_live_slots::kTip);
+    dual_brush.m_tip_texture ?
+        dual_brush.m_tip_texture->bind() :
+        unbind_texture_2d();
+}
+
+void bind_stroke_preview_main_pass_textures(
+    const Brush& brush,
+    Texture2D& stroke_destination_texture,
+    RTT& mixer_rtt,
+    bool copy_stroke_destination,
+    bool uses_mixer)
+{
+    set_active_texture_unit(stroke_preview_live_slots::kTip);
+    brush.m_tip_texture ?
+        brush.m_tip_texture->bind() :
+        unbind_texture_2d();
+
+    if (copy_stroke_destination)
+    {
+        set_active_texture_unit(stroke_preview_live_slots::kDestination);
+        stroke_destination_texture.bind();
+    }
+
+    set_active_texture_unit(stroke_preview_live_slots::kPattern);
+    brush.m_pattern_texture ?
+        brush.m_pattern_texture->bind() :
+        unbind_texture_2d();
+
+    set_active_texture_unit(stroke_preview_live_slots::kMixer);
+    uses_mixer ? mixer_rtt.bindTexture() : unbind_texture_2d();
+}
+
+void execute_stroke_preview_background_capture_pass(
+    glm::vec2 size,
+    bool colorize,
+    Texture2D& background_texture,
+    const std::function<void()>& draw_checkerboard)
+{
+    pp::panopainter::execute_legacy_stroke_preview_background_capture(
+        [&] {
+            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 = colorize,
+                });
+        },
+        [&] {
+            draw_checkerboard();
+        },
+        [&] {
+            background_texture.bind();
+        },
+        [](
+            int src_x,
+            int src_y,
+            int dst_x,
+            int dst_y,
+            int width,
+            int height) {
+            copy_framebuffer_to_texture_2d(src_x, src_y, dst_x, dst_y, width, height);
+        },
+        pp::panopainter::LegacyStrokePreviewCopySize {
+            .width = static_cast<int>(size.x),
+            .height = static_cast<int>(size.y),
+        });
+}
+
+void copy_stroke_preview_result_to_texture(Texture2D& preview_texture, glm::vec2 size)
+{
+    pp::panopainter::copy_legacy_stroke_preview_texture(
+        [&] {
+            preview_texture.bind();
+        },
+        [](
+            int src_x,
+            int src_y,
+            int dst_x,
+            int dst_y,
+            int width,
+            int height) {
+            copy_framebuffer_to_texture_2d(src_x, src_y, dst_x, dst_y, width, height);
+        },
+        pp::panopainter::LegacyStrokePreviewCopySize {
+            .width = static_cast<int>(size.x),
+            .height = static_cast<int>(size.y),
+        });
+}
+
 template <typename ClearTarget, typename ComputeFrames, typename BeforeFrame, typename DrawSample>
 void execute_stroke_preview_live_pass(
     Texture2D& output_texture,
@@ -471,11 +583,10 @@ void NodeStrokePreview::draw_stroke_immediate()
     apply_stroke_preview_viewport(0, 0, m_rtt.getWidth(), m_rtt.getHeight());
     m_rtt.bindFramebuffer();
     m_rtt.clear();
-    m_sampler_mipmap.bind(0);
+    bind_stroke_preview_live_samplers(
-    m_sampler_linear.bind(1);
+        m_sampler_mipmap,
-    m_sampler_linear_repeat.bind(2);
+        m_sampler_linear,
-    m_sampler_linear.bind(3);
+        m_sampler_linear_repeat);
-    m_sampler_linear.bind(4);
 
     const auto& b = m_brush;
 
@@ -581,10 +692,7 @@ void NodeStrokePreview::draw_stroke_immediate()
     if (material.dual_pass.enabled)
     {
         pp::panopainter::setup_legacy_stroke_dual_shader(material.dual_pass.uses_pattern);
-        set_active_texture_unit(0U);
+        bind_stroke_preview_dual_pass_textures(*dual_brush);
-        dual_brush->m_tip_texture ?
-            dual_brush->m_tip_texture->bind() :
-            unbind_texture_2d();
         execute_stroke_preview_live_pass(
             m_tex_dual,
             size,
@@ -605,35 +713,12 @@ void NodeStrokePreview::draw_stroke_immediate()
 
     // CHEKCERBOARD
 
-    pp::panopainter::execute_legacy_stroke_preview_background_capture(
+    execute_stroke_preview_background_capture_pass(
-        [&] {
+        size,
-            // copy background color to tex2
+        b->m_tip_mix > 0.f || b->m_blend_mode != 0,
-            const float aspect = size.x / size.y;
+        m_tex_background,
-            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();
-        },
-        [&] {
-            //m_rtt.clear({ .3f, .3f, .3f, 1.f });
-            m_tex_background.bind();
-        },
-        [](
-            int src_x,
-            int src_y,
-            int dst_x,
-            int dst_y,
-            int width,
-            int height) {
-            copy_framebuffer_to_texture_2d(src_x, src_y, dst_x, dst_y, width, height);
-        },
-        pp::panopainter::LegacyStrokePreviewCopySize {
-            .width = static_cast<int>(size.x),
-            .height = static_cast<int>(size.y),
         });
 
     // DRAW MAIN BRUSH
@@ -645,19 +730,12 @@ void NodeStrokePreview::draw_stroke_immediate()
         b->m_tip_wet,
         b->m_tip_noise);
 
-    set_active_texture_unit(0U);
+    bind_stroke_preview_main_pass_textures(
-    b->m_tip_texture->bind();
+        *b,
-    if (copy_stroke_destination)
+        m_tex,
-    {
+        m_rtt_mixer,
-        set_active_texture_unit(1U);
+        copy_stroke_destination,
-        m_tex.bind(); // tmp swap for blending
+        preview_composite_plan.uses_mixer);
-    }
-    set_active_texture_unit(2U);
-    b->m_pattern_texture ?
-        b->m_pattern_texture->bind() :
-        unbind_texture_2d();
-    set_active_texture_unit(3U);
-    preview_composite_plan.uses_mixer ? m_rtt_mixer.bindTexture() : unbind_texture_2d();
     execute_stroke_preview_live_pass(
         m_tex,
         size,
@@ -682,7 +760,7 @@ void NodeStrokePreview::draw_stroke_immediate()
         [&](auto& frame, Texture2D& blend_texture, bool copy_destination) {
             /*auto rect =*/ stroke_draw_samples(frame.shapes, blend_texture, copy_destination);
         });
-    set_active_texture_unit(3U);
+    set_active_texture_unit(stroke_preview_live_slots::kMixer);
     m_rtt_mixer.unbindTexture();
 
     // COMPOSITE
@@ -704,23 +782,7 @@ void NodeStrokePreview::draw_stroke_immediate()
         });
 
     // copy the result to the actual preview
-    pp::panopainter::copy_legacy_stroke_preview_texture(
+    copy_stroke_preview_result_to_texture(m_tex_preview, size);
-        [&] {
-            m_tex_preview.bind();
-        },
-        [](
-            int src_x,
-            int src_y,
-            int dst_x,
-            int dst_y,
-            int width,
-            int height) {
-            copy_framebuffer_to_texture_2d(src_x, src_y, dst_x, dst_y, width, height);
-        },
-        pp::panopainter::LegacyStrokePreviewCopySize {
-            .width = static_cast<int>(size.x),
-            .height = static_cast<int>(size.y),
-        });
 
     m_rtt.unbindFramebuffer();