subsurface: use geometry-aware damage and recurse into nested trees (#13933)

* subsurface: use geometry-aware damage and recurse into nested trees

Replace per-surface damageSurface() calls in recheckDamageForSubsurfaces()
with box-based damage that tracks each subsurface's last known global
position and size. When geometry changes, both the old and new areas are
damaged to correctly clear stale pixels and paint the new location.

Additionally, recurse into child subsurfaces so that nested subsurface
trees are properly damage-checked, with a depth limit of 32 to guard
against cycles. Cached geometry is invalidated on map/unmap to avoid
stale comparisons across surface lifecycle transitions.

* clang-format

2 files changed, 33 insertions, 5 deletions

diff --git a/src/desktop/view/Subsurface.cpp b/src/desktop/view/Subsurface.cpp
index c601c00e..c3c985df 100644
--- a/src/desktop/view/Subsurface.cpp
+++ b/src/desktop/view/Subsurface.cpp
@@ -128,10 +128,32 @@ void CSubsurface::checkSiblingDamage() {
     }
 }
 
-void CSubsurface::recheckDamageForSubsurfaces() {
+void CSubsurface::recheckDamageForSubsurfaces(int depth) {
+    if (depth > 32)
+        return;
+
     for (auto const& n : m_children) {
         const auto COORDS = n->coordsGlobal();
-        g_pHyprRenderer->damageSurface(n->wlSurface()->resource(), COORDS.x, COORDS.y);
+        const auto SIZE   = n->size();
+
+        const bool GEOMETRYUNCHANGED = n->m_hasLastRecheckGeometry && COORDS.x == n->m_lastRecheckGlobalPos.x && COORDS.y == n->m_lastRecheckGlobalPos.y &&
+            SIZE.x == n->m_lastRecheckGlobalSize.x && SIZE.y == n->m_lastRecheckGlobalSize.y;
+
+        if (!GEOMETRYUNCHANGED) {
+            // damage the old area to clear stale pixels
+            if (n->m_hasLastRecheckGeometry)
+                g_pHyprRenderer->damageBox(CBox{n->m_lastRecheckGlobalPos, n->m_lastRecheckGlobalSize}.expand(4));
+
+            n->m_lastRecheckGlobalPos   = COORDS;
+            n->m_lastRecheckGlobalSize  = SIZE;
+            n->m_hasLastRecheckGeometry = true;
+
+            // damage the new area
+            g_pHyprRenderer->damageBox(CBox{COORDS, SIZE}.expand(4));
+        }
+
+        // recurse into children to handle nested subsurface trees
+        n->recheckDamageForSubsurfaces(depth + 1);
     }
 }
 
@@ -194,8 +216,9 @@ void CSubsurface::onNewSubsurface(SP<CWLSubsurfaceResource> pSubsurface) {
 }
 
 void CSubsurface::onMap() {
-    m_lastSize     = m_wlSurface->resource()->m_current.size;
-    m_lastPosition = m_subsurface->m_position;
+    m_lastSize               = m_wlSurface->resource()->m_current.size;
+    m_lastPosition           = m_subsurface->m_position;
+    m_hasLastRecheckGeometry = false;
 
     const auto COORDS = coordsGlobal();
     CBox       box{COORDS, m_lastSize};
@@ -209,6 +232,8 @@ void CSubsurface::onMap() {
 void CSubsurface::onUnmap() {
     damageLastArea();
 
+    m_hasLastRecheckGeometry = false;
+
     if (m_wlSurface->resource() == Desktop::focusState()->surface())
         g_pInputManager->releaseAllMouseButtons();
 
diff --git a/src/desktop/view/Subsurface.hpp b/src/desktop/view/Subsurface.hpp
index ab74f48c..bb2f6780 100644
--- a/src/desktop/view/Subsurface.hpp
+++ b/src/desktop/view/Subsurface.hpp
@@ -40,7 +40,7 @@ namespace Desktop::View {
         void                           onMap();
         void                           onUnmap();
 
-        void                           recheckDamageForSubsurfaces();
+        void                           recheckDamageForSubsurfaces(int depth = 0);
 
         WP<Desktop::View::CSubsurface> m_self;
 
@@ -58,6 +58,9 @@ namespace Desktop::View {
         WP<CWLSubsurfaceResource> m_subsurface;
         Vector2D                  m_lastSize     = {};
         Vector2D                  m_lastPosition = {};
+        Vector2D                  m_lastRecheckGlobalPos;
+        Vector2D                  m_lastRecheckGlobalSize;
+        bool                      m_hasLastRecheckGeometry = false;
 
         // if nullptr, means it's a dummy node
         WP<Desktop::View::CSubsurface>              m_parent;