Resolve axis control geometry once per dispatch

CHANGELOG.md

@@ -4,6 +4,8 @@ Dated delivery history and release records. Each release is a `## vX.Y.Z — YYY
 
 ## Unreleased
 
+- Resolve `SplitPane` and `Scrollbar` geometry once per dispatched event and reuse it to reconcile active drags.
+
 - Shared keyboard and gamepad range adjustments between `SplitPane` and `Scrollbar`, preserving their existing focus, drag and command behavior.
 
 - Shared the generated label and draft field between `NumberInput` and `VectorInput` components, preserving their part IDs, source mappings and clipping rules.

include/tessera/input/scrollbar.hpp

@@ -43,6 +43,7 @@ class ScrollbarDispatcher final {
     void reset() noexcept { drag_.reset(); }
 
 private:
+    Result<std::optional<ScrollbarGeometry>> reconcile_geometry(const HitTestInput&);
     struct Drag {
         PointerId pointer;
         float grab;

include/tessera/input/split_pane.hpp

@@ -37,6 +37,7 @@ class SplitPaneDispatcher final {
     void reset() noexcept { drag_.reset(); }
 
 private:
+    Result<std::optional<SplitPaneGeometry>> reconcile_geometry(const HitTestInput&);
     struct Drag {
         PointerId pointer;
         float grab;

src/input/scrollbar.cpp

@@ -89,25 +89,26 @@ Result<std::optional<ScrollbarGeometry>> scrollbar_geometry(const HitTestInput&
     return {view, {}};
 }
 
-Result<ScrollbarDispatchResult> ScrollbarDispatcher::refresh(const HitTestInput& input) {
+Result<std::optional<ScrollbarGeometry>> ScrollbarDispatcher::reconcile_geometry(const HitTestInput& input) {
     if (!std::isfinite(step_) || step_ <= 0)
         return {std::nullopt,
                 {{"scrollbar_step", Severity::error, "/step", "Supply a finite positive keyboard step."}}};
     auto geometry = scrollbar_geometry(input, id_, scroll_id_);
+    if (!geometry || !drag_) return geometry;
+    const auto& view = *geometry.value;
+    if (!view || !view->enabled || drag_->axis != view->axis ||
+        drag_->thumb_size != along(view->axis, view->bounds.size) ||
+        drag_->track_size != along(view->axis, view->track.size) || drag_->maximum != view->maximum ||
+        input.tree->get(view->thumb)->events.at("activate") != drag_->action)
+        reset();
+    return geometry;
+}
+
+Result<ScrollbarDispatchResult> ScrollbarDispatcher::refresh(const HitTestInput& input) {
+    auto geometry = reconcile_geometry(input);
     if (!geometry) return {std::nullopt, std::move(geometry.diagnostics)};
     ScrollbarDispatchResult result;
-    if (!*geometry.value) {
-        reset();
-        return {result, {}};
-    }
-    const auto& view = **geometry.value;
-    result.update = ScrollUpdate{view.container, view.offset};
-    const auto* node = input.tree->get(view.thumb);
-    if (drag_ &&
-        (!view.enabled || drag_->axis != view.axis || drag_->thumb_size != along(view.axis, view.bounds.size) ||
-         drag_->track_size != along(view.axis, view.track.size) || drag_->maximum != view.maximum ||
-         node->events.at("activate") != drag_->action))
-        reset();
+    if (const auto& view = *geometry.value) result.update = ScrollUpdate{view->container, view->offset};
     return {result, {}};
 }
 
@@ -118,9 +119,7 @@ Result<ScrollbarDispatchResult> ScrollbarDispatcher::dispatch(const HitTestInput
     errors.insert(errors.end(), semantic_errors.begin(), semantic_errors.end());
     if (!errors.empty()) return {std::nullopt, std::move(errors)};
     auto candidate = *this;
-    auto refreshed = candidate.refresh(input);
-    if (!refreshed) return refreshed;
-    auto geometry = scrollbar_geometry(input, id_, scroll_id_);
+    auto geometry = candidate.reconcile_geometry(input);
     if (!geometry) return {std::nullopt, std::move(geometry.diagnostics)};
     ScrollbarDispatchResult result;
     if (!*geometry.value || !(**geometry.value).enabled) {

src/input/split_pane.cpp

@@ -59,24 +59,25 @@ Result<std::optional<SplitPaneGeometry>> split_pane_geometry(const HitTestInput&
             {}};
 }
 
-Result<SplitPaneDispatchResult> SplitPaneDispatcher::refresh(const HitTestInput& input) {
+Result<std::optional<SplitPaneGeometry>> SplitPaneDispatcher::reconcile_geometry(const HitTestInput& input) {
     if (!std::isfinite(step_) || step_ <= 0)
         return {std::nullopt,
                 {{"split_pane_step", Severity::error, "/step", "Supply a finite positive keyboard step."}}};
     auto geometry = split_pane_geometry(input, id_);
+    if (!geometry || !drag_) return geometry;
+    const auto& view = *geometry.value;
+    if (!view || !view->enabled || drag_->direction != view->direction ||
+        drag_->handle_size != extent(view->bounds.size, view->direction) ||
+        input.tree->get(view->handle)->events.at("activate") != drag_->action)
+        reset();
+    return geometry;
+}
+
+Result<SplitPaneDispatchResult> SplitPaneDispatcher::refresh(const HitTestInput& input) {
+    auto geometry = reconcile_geometry(input);
     if (!geometry) return {std::nullopt, std::move(geometry.diagnostics)};
     SplitPaneDispatchResult result;
-    if (!*geometry.value) {
-        reset();
-        return {result, {}};
-    }
-    const auto& view = **geometry.value;
-    result.size = view.size;
-    const auto* node = input.tree->get(view.handle);
-    if (drag_ && (!view.enabled || drag_->direction != view.direction ||
-                  drag_->handle_size != extent(view.bounds.size, view.direction) ||
-                  node->events.at("activate") != drag_->action))
-        reset();
+    if (const auto& view = *geometry.value) result.size = view->size;
     return {result, {}};
 }
 
@@ -87,9 +88,7 @@ Result<SplitPaneDispatchResult> SplitPaneDispatcher::dispatch(const HitTestInput
     errors.insert(errors.end(), semantic_errors.begin(), semantic_errors.end());
     if (!errors.empty()) return {std::nullopt, std::move(errors)};
     auto candidate = *this;
-    auto refreshed = candidate.refresh(input);
-    if (!refreshed) return refreshed;
-    auto geometry = split_pane_geometry(input, id_);
+    auto geometry = candidate.reconcile_geometry(input);
     if (!geometry) return {std::nullopt, std::move(geometry.diagnostics)};
     SplitPaneDispatchResult result;
     if (!*geometry.value || !(**geometry.value).enabled) {