Extract preview main pass texture dispatch

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;