Share retained stroke preview mix executor

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::stroke_draw_mix()`
+  now routes retained mix-pass shader setup plus framebuffer/state/input/draw
+  ordering through `execute_legacy_node_stroke_preview_mix_pass(...)`; the
+  preview node keeps only the concrete GL save/restore, texture-object bind,
+  and plane-draw callbacks.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` live-pass
   sampler bind/unbind plus semantic texture-input dispatch now route through
   retained stroke execution helpers; concrete GL object mapping, framebuffer

docs/modernization/roadmap.md

@@ -3150,6 +3150,11 @@ Results:
   framebuffer bind/unbind, viewport/scissor/blend state, texture-slot
   binding, and final plane draw, while material planning and shader uniform
   setup remain in the preview node.
+- `NodeStrokePreview::stroke_draw_mix()` now routes retained mix-pass shader
+  setup plus framebuffer/state/input/draw ordering through
+  `execute_legacy_node_stroke_preview_mix_pass(...)`, while the preview node
+  keeps only the concrete GL save/restore, texture-object bind, and plane-draw
+  callbacks.
 - `pp_paint_renderer_stroke_execution_tests` now covers retained stroke texture
   input binding order, sample execution destination-copy behavior, live-pass
   face-framebuffer dirty tracking, and pad-face destination-copy behavior

docs/modernization/tasks.md

@@ -509,6 +509,14 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `NodeStrokePreview::stroke_draw_mix()` now routes retained
+  mix-pass shader setup plus framebuffer/state/input/draw ordering through
+  `execute_legacy_node_stroke_preview_mix_pass(...)`, with compositor coverage
+  locking the retained callback order and shader-plan handoff. The preview node
+  keeps only the concrete GL save/restore, texture-object bind, and plane-draw
+  callbacks. Next slice should target another retained preview or canvas stroke
+  seam without reopening the landed preview sample, material-planning,
+  pass-sequence, or final-composite helpers.
 - 2026-06-13: `NodeStrokePreview::draw_stroke_immediate()` now routes
   dual-pass/background/main-pass/final-composite/copy-back ordering through
   `execute_legacy_node_stroke_preview_pass_sequence(...)`; the remaining local

src/legacy_node_stroke_preview_execution_services.h

@@ -87,6 +87,24 @@ struct LegacyNodeStrokePreviewMixPassRequest {
     int blend_mode = 0;
 };
 
+struct LegacyNodeStrokePreviewMixExecutionRequest {
+    LegacyNodeStrokePreviewMixPassPlan::ShaderPlan shader {};
+    int mixer_width = 0;
+    int mixer_height = 0;
+    int scissor_x = 0;
+    int scissor_y = 0;
+    int scissor_width = 0;
+    int scissor_height = 0;
+    std::function<void()> save_state;
+    std::function<void(const LegacyNodeStrokePreviewMixPassPlan::ShaderPlan&)> setup_mix_shader;
+    std::function<void()> bind_mixer_framebuffer;
+    std::function<void(int, int, int, int, int, int)> configure_mix_target_state;
+    std::function<void()> bind_mix_inputs;
+    std::function<void()> draw_mix;
+    std::function<void()> unbind_mixer_framebuffer;
+    std::function<void()> restore_state;
+};
+
 [[nodiscard]] inline LegacyNodeStrokePreviewMixPassPlan plan_legacy_node_stroke_preview_mix_pass(
     const LegacyNodeStrokePreviewMixPassRequest& request) noexcept
 {
@@ -130,6 +148,39 @@ struct LegacyNodeStrokePreviewMixPassRequest {
     return plan;
 }
 
+[[nodiscard]] inline bool execute_legacy_node_stroke_preview_mix_pass(
+    const LegacyNodeStrokePreviewMixExecutionRequest& request)
+{
+    if (request.mixer_width <= 0 ||
+        request.mixer_height <= 0 ||
+        !request.save_state ||
+        !request.setup_mix_shader ||
+        !request.bind_mixer_framebuffer ||
+        !request.configure_mix_target_state ||
+        !request.bind_mix_inputs ||
+        !request.draw_mix ||
+        !request.unbind_mixer_framebuffer ||
+        !request.restore_state) {
+        return false;
+    }
+
+    request.save_state();
+    request.setup_mix_shader(request.shader);
+    request.bind_mixer_framebuffer();
+    request.configure_mix_target_state(
+        request.mixer_width,
+        request.mixer_height,
+        request.scissor_x,
+        request.scissor_y,
+        request.scissor_width,
+        request.scissor_height);
+    request.bind_mix_inputs();
+    request.draw_mix();
+    request.unbind_mixer_framebuffer();
+    request.restore_state();
+    return true;
+}
+
 struct LegacyNodeStrokePreviewPassSequenceRequest {
     bool dual_pass_enabled = false;
     std::function<void()> prepare_dual_pass;

src/node_stroke_preview.cpp

@@ -124,18 +124,6 @@ struct StrokePreviewCompositePassInputs {
     std::function<void()> draw_composite;
 };
 
-struct StrokePreviewMixPassInputs {
-    glm::vec2 scissor_min;
-    glm::vec2 scissor_size;
-    RTT& mixer_rtt;
-    Texture2D& background_texture;
-    RTT& stroke_rtt;
-    Texture2D& dual_texture;
-    const Brush& brush;
-    Sampler& linear_sampler;
-    std::function<void()> draw_mix;
-};
-
 pp::panopainter::LegacyNodeStrokePreviewMixPassRequest make_stroke_preview_mix_pass_request(
     const Brush& brush,
     glm::vec2 resolution) noexcept
@@ -190,40 +178,6 @@ pp::panopainter::LegacyStrokeCompositeUniforms make_stroke_preview_mix_composite
     };
 }
 
-void execute_stroke_preview_mix_pass(const StrokePreviewMixPassInputs& inputs)
-{
-    gl_state gl;
-    gl.save();
-
-    inputs.mixer_rtt.bindFramebuffer();
-
-    apply_stroke_preview_viewport(0, 0, inputs.mixer_rtt.getWidth(), inputs.mixer_rtt.getHeight());
-    apply_stroke_preview_capability(pp::renderer::gl::depth_test_state(), false);
-    apply_stroke_preview_capability(pp::renderer::gl::scissor_test_state(), true);
-    apply_stroke_preview_capability(pp::renderer::gl::blend_state(), false);
-    apply_stroke_preview_scissor(
-        static_cast<int>(inputs.scissor_min.x),
-        static_cast<int>(inputs.scissor_min.y),
-        static_cast<int>(inputs.scissor_size.x),
-        static_cast<int>(inputs.scissor_size.y));
-
-    inputs.linear_sampler.bind(stroke_preview_composite_slots::kBackground);
-    set_active_texture_unit(stroke_preview_composite_slots::kBackground);
-    inputs.background_texture.bind();
-    set_active_texture_unit(stroke_preview_composite_slots::kStroke);
-    inputs.stroke_rtt.bindTexture();
-    set_active_texture_unit(stroke_preview_composite_slots::kDual);
-    inputs.dual_texture.bind();
-    set_active_texture_unit(stroke_preview_composite_slots::kPattern);
-    inputs.brush.m_pattern_texture ?
-        inputs.brush.m_pattern_texture->bind() :
-        unbind_texture_2d();
-    inputs.draw_mix();
-
-    inputs.mixer_rtt.unbindFramebuffer();
-    gl.restore();
-}
-
 void execute_stroke_preview_final_composite_pass(const StrokePreviewCompositePassInputs& inputs)
 {
     pp::panopainter::execute_legacy_stroke_preview_final_composite(
@@ -607,23 +561,67 @@ void NodeStrokePreview::stroke_draw_mix(const glm::vec2& bb_min, const glm::vec2
     const auto& b = m_brush;
     const auto mix_pass = pp::panopainter::plan_legacy_node_stroke_preview_mix_pass(
         make_stroke_preview_mix_pass_request(*b, m_size));
-    pp::panopainter::setup_legacy_stroke_composite_shader(
+    gl_state gl;
-        make_stroke_preview_mix_composite_uniforms(mix_pass.shader));
+    [[maybe_unused]] const bool mix_ok = pp::panopainter::execute_legacy_node_stroke_preview_mix_pass(
-
+        pp::panopainter::LegacyNodeStrokePreviewMixExecutionRequest {
-    execute_stroke_preview_mix_pass(
+            .shader = mix_pass.shader,
-        StrokePreviewMixPassInputs {
+            .mixer_width = m_rtt_mixer.getWidth(),
-            .scissor_min = bb_min,
+            .mixer_height = m_rtt_mixer.getHeight(),
-            .scissor_size = bb_sz,
+            .scissor_x = static_cast<int>(bb_min.x),
-            .mixer_rtt = m_rtt_mixer,
+            .scissor_y = static_cast<int>(bb_min.y),
-            .background_texture = m_tex_background,
+            .scissor_width = static_cast<int>(bb_sz.x),
-            .stroke_rtt = m_rtt,
+            .scissor_height = static_cast<int>(bb_sz.y),
-            .dual_texture = m_tex_dual,
+            .save_state = [&] {
-            .brush = *b,
+                gl.save();
-            .linear_sampler = m_sampler_linear,
+            },
+            .setup_mix_shader = [&](const pp::panopainter::LegacyNodeStrokePreviewMixPassPlan::ShaderPlan& shader_plan) {
+                pp::panopainter::setup_legacy_stroke_composite_shader(
+                    make_stroke_preview_mix_composite_uniforms(shader_plan));
+            },
+            .bind_mixer_framebuffer = [&] {
+                m_rtt_mixer.bindFramebuffer();
+            },
+            .configure_mix_target_state = [&](
+                int mixer_width,
+                int mixer_height,
+                int scissor_x,
+                int scissor_y,
+                int scissor_width,
+                int scissor_height) {
+                apply_stroke_preview_viewport(0, 0, mixer_width, mixer_height);
+                apply_stroke_preview_capability(pp::renderer::gl::depth_test_state(), false);
+                apply_stroke_preview_capability(pp::renderer::gl::scissor_test_state(), true);
+                apply_stroke_preview_capability(pp::renderer::gl::blend_state(), false);
+                apply_stroke_preview_scissor(
+                    scissor_x,
+                    scissor_y,
+                    scissor_width,
+                    scissor_height);
+            },
+            .bind_mix_inputs = [&] {
+                m_sampler_linear.bind(stroke_preview_composite_slots::kBackground);
+                set_active_texture_unit(stroke_preview_composite_slots::kBackground);
+                m_tex_background.bind();
+                set_active_texture_unit(stroke_preview_composite_slots::kStroke);
+                m_rtt.bindTexture();
+                set_active_texture_unit(stroke_preview_composite_slots::kDual);
+                m_tex_dual.bind();
+                set_active_texture_unit(stroke_preview_composite_slots::kPattern);
+                b->m_pattern_texture ?
+                    b->m_pattern_texture->bind() :
+                    unbind_texture_2d();
+            },
             .draw_mix = [&] {
                 m_plane.draw_fill();
             },
+            .unbind_mixer_framebuffer = [&] {
+                m_rtt_mixer.unbindFramebuffer();
+            },
+            .restore_state = [&] {
+                gl.restore();
+            },
         });
+    assert(mix_ok);
 }
 
 glm::vec4 NodeStrokePreview::stroke_draw_samples(

tests/paint_renderer/compositor_tests.cpp

@@ -2240,6 +2240,96 @@ void legacy_node_stroke_preview_mix_pass_adapter_preserves_retained_material_and
     PP_EXPECT(h, plan.shader.use_pattern == plan.material.composite_pass.use_pattern);
 }
 
+void legacy_node_stroke_preview_mix_executor_preserves_setup_and_draw_order(pp::tests::Harness& h)
+{
+    std::vector<std::string> steps;
+    pp::panopainter::LegacyNodeStrokePreviewMixPassPlan::ShaderPlan observed_shader {};
+
+    const bool ok = pp::panopainter::execute_legacy_node_stroke_preview_mix_pass(
+        pp::panopainter::LegacyNodeStrokePreviewMixExecutionRequest {
+            .shader = pp::panopainter::LegacyNodeStrokePreviewMixPassPlan::ShaderPlan {
+                .resolution = glm::vec2(128.0F, 64.0F),
+                .pattern_scale = glm::vec2(-0.25F, 0.25F),
+                .pattern_invert = 1.0F,
+                .pattern_brightness = 0.6F,
+                .pattern_contrast = 0.8F,
+                .pattern_depth = 0.9F,
+                .pattern_blend_mode = 7,
+                .pattern_offset = glm::vec2(0.5F, 0.5F),
+                .blend_mode = 5,
+                .use_dual = true,
+                .dual_blend_mode = 9,
+                .dual_alpha = 0.4F,
+                .use_pattern = true,
+            },
+            .mixer_width = 128,
+            .mixer_height = 64,
+            .scissor_x = 11,
+            .scissor_y = 12,
+            .scissor_width = 13,
+            .scissor_height = 14,
+            .save_state = [&] {
+                steps.emplace_back("save");
+            },
+            .setup_mix_shader = [&](const auto& shader) {
+                observed_shader = shader;
+                steps.emplace_back("setup");
+            },
+            .bind_mixer_framebuffer = [&] {
+                steps.emplace_back("bind-framebuffer");
+            },
+            .configure_mix_target_state = [&](int width, int height, int x, int y, int scissor_width, int scissor_height) {
+                steps.emplace_back(
+                    "configure:" +
+                    std::to_string(width) + "," +
+                    std::to_string(height) + "," +
+                    std::to_string(x) + "," +
+                    std::to_string(y) + "," +
+                    std::to_string(scissor_width) + "," +
+                    std::to_string(scissor_height));
+            },
+            .bind_mix_inputs = [&] {
+                steps.emplace_back("bind-inputs");
+            },
+            .draw_mix = [&] {
+                steps.emplace_back("draw");
+            },
+            .unbind_mixer_framebuffer = [&] {
+                steps.emplace_back("unbind-framebuffer");
+            },
+            .restore_state = [&] {
+                steps.emplace_back("restore");
+            },
+        });
+
+    PP_EXPECT(h, ok);
+    PP_EXPECT(h, near(observed_shader.resolution, glm::vec2(128.0F, 64.0F)));
+    PP_EXPECT(h, near(observed_shader.pattern_scale, glm::vec2(-0.25F, 0.25F)));
+    PP_EXPECT(h, observed_shader.use_dual);
+    PP_EXPECT(h, observed_shader.use_pattern);
+    PP_EXPECT(h, observed_shader.dual_blend_mode == 9);
+    PP_EXPECT(h, near(observed_shader.dual_alpha, 0.4F));
+
+    const std::vector<std::string> expected_steps {
+        "save",
+        "setup",
+        "bind-framebuffer",
+        "configure:128,64,11,12,13,14",
+        "bind-inputs",
+        "draw",
+        "unbind-framebuffer",
+        "restore",
+    };
+    PP_EXPECT(h, steps == expected_steps);
+
+    const bool invalid = pp::panopainter::execute_legacy_node_stroke_preview_mix_pass(
+        pp::panopainter::LegacyNodeStrokePreviewMixExecutionRequest {
+            .mixer_width = 128,
+            .mixer_height = 64,
+        });
+    PP_EXPECT(h, !invalid);
+}
+
 void legacy_node_stroke_preview_pass_sequence_preserves_dual_main_and_composite_order(pp::tests::Harness& h)
 {
     std::vector<std::string> steps;
@@ -2300,6 +2390,37 @@ void legacy_node_stroke_preview_pass_sequence_preserves_dual_main_and_composite_
     };
     PP_EXPECT(h, steps == single_steps);
 
+    steps.clear();
+    const bool missing_dual_prepare =
+        pp::panopainter::execute_legacy_node_stroke_preview_pass_sequence(
+            pp::panopainter::LegacyNodeStrokePreviewPassSequenceRequest {
+                .dual_pass_enabled = true,
+                .prepare_dual_pass = {},
+                .execute_dual_pass = [&] {
+                    steps.emplace_back("execute_dual");
+                },
+                .capture_background = [&] {
+                    steps.emplace_back("capture_background");
+                },
+                .prepare_main_pass = [&] {
+                    steps.emplace_back("prepare_main");
+                },
+                .execute_main_pass = [&] {
+                    steps.emplace_back("execute_main");
+                },
+                .finish_main_pass = [&] {
+                    steps.emplace_back("finish_main");
+                },
+                .execute_final_composite = [&] {
+                    steps.emplace_back("execute_composite");
+                },
+                .copy_preview_result = [&] {
+                    steps.emplace_back("copy_preview");
+                },
+            });
+    PP_EXPECT(h, !missing_dual_prepare);
+    PP_EXPECT(h, steps.empty());
+
     const bool missing_required =
         pp::panopainter::execute_legacy_node_stroke_preview_pass_sequence(
             pp::panopainter::LegacyNodeStrokePreviewPassSequenceRequest {});
@@ -2760,6 +2881,9 @@ int main()
     harness.run(
         "legacy_node_stroke_preview_mix_pass_adapter_preserves_retained_material_and_uniforms",
         legacy_node_stroke_preview_mix_pass_adapter_preserves_retained_material_and_uniforms);
+    harness.run(
+        "legacy_node_stroke_preview_mix_executor_preserves_setup_and_draw_order",
+        legacy_node_stroke_preview_mix_executor_preserves_setup_and_draw_order);
     harness.run(
         "legacy_node_stroke_preview_pass_sequence_preserves_dual_main_and_composite_order",
         legacy_node_stroke_preview_pass_sequence_preserves_dual_main_and_composite_order);