engine: sync editor rendering and ui changes

engine/src/UI/Widgets/UIScrollModel.cpp

@@ -0,0 +1,67 @@
+#include <XCEngine/UI/Widgets/UIScrollModel.h>
+
+#include <algorithm>
+#include <cmath>
+
+namespace XCEngine {
+namespace UI {
+namespace Widgets {
+
+float ComputeUIScrollOverflow(float contentExtent, float viewportExtent) {
+    return (std::max)(0.0f, contentExtent - viewportExtent);
+}
+
+float ClampUIScrollOffset(float offset, float contentExtent, float viewportExtent) {
+    return (std::max)(0.0f, (std::min)(offset, ComputeUIScrollOverflow(contentExtent, viewportExtent)));
+}
+
+UIScrollWheelResult ApplyUIScrollWheel(
+    float offset,
+    float wheelDelta,
+    float contentExtent,
+    float viewportExtent,
+    float wheelStep,
+    float epsilon) {
+    UIScrollWheelResult result = {};
+    result.offsetBefore = ClampUIScrollOffset(offset, contentExtent, viewportExtent);
+    result.overflow = ComputeUIScrollOverflow(contentExtent, viewportExtent);
+    result.offsetAfter = result.offsetBefore;
+    if (result.overflow <= 0.0f || std::fabs(wheelDelta) <= epsilon || wheelStep <= 0.0f) {
+        return result;
+    }
+
+    const float scrollUnits = wheelDelta / 120.0f;
+    result.offsetAfter = ClampUIScrollOffset(
+        result.offsetBefore - scrollUnits * wheelStep,
+        contentExtent,
+        viewportExtent);
+    result.changed = std::fabs(result.offsetAfter - result.offsetBefore) > epsilon;
+    return result;
+}
+
+float EnsureUIScrollOffsetVisible(
+    float offset,
+    float itemStart,
+    float itemExtent,
+    float contentExtent,
+    float viewportExtent) {
+    const float clampedOffset = ClampUIScrollOffset(offset, contentExtent, viewportExtent);
+    if (viewportExtent <= 0.0f || itemExtent <= 0.0f) {
+        return clampedOffset;
+    }
+
+    const float itemEnd = itemStart + itemExtent;
+    const float viewportEnd = clampedOffset + viewportExtent;
+    float nextOffset = clampedOffset;
+    if (itemStart < clampedOffset) {
+        nextOffset = itemStart;
+    } else if (itemEnd > viewportEnd) {
+        nextOffset = itemEnd - viewportExtent;
+    }
+
+    return ClampUIScrollOffset(nextOffset, contentExtent, viewportExtent);
+}
+
+} // namespace Widgets
+} // namespace UI
+} // namespace XCEngine