input: implement follow_mouse_shrink (#13707)

* input: implement follow_mouse_shrink

Add a new config option `input:follow_mouse_shrink` (INT, 0-300, default 0)
that shrinks inactive window hitboxes by the specified number of pixels for
focus detection purposes. This creates a dead zone in gaps between windows
where moving the cursor will not trigger a focus change.

The shrink only applies to inactive (non-focused) windows and only during
mouse-move focus checks (follow_mouse = 1). Click and scroll interactions
are unaffected — clicking on a window in the shrunk area still works
normally once the window is focused.

Closes #9973

* tests: add integration test for follow_mouse_shrink

6 files changed, 25 insertions, 4 deletions

diff --git a/src/Compositor.cpp b/src/Compositor.cpp
index 92f81fc6..f823b62c 100644
--- a/src/Compositor.cpp
+++ b/src/Compositor.cpp
@@ -895,7 +895,7 @@ bool CCompositor::monitorExists(PHLMONITOR pMonitor) {
     return std::ranges::any_of(m_realMonitors, [&](const PHLMONITOR& m) { return m == pMonitor; });
 }
 
-PHLWINDOW CCompositor::vectorToWindowUnified(const Vector2D& pos, uint8_t properties, PHLWINDOW pIgnoreWindow) {
+PHLWINDOW CCompositor::vectorToWindowUnified(const Vector2D& pos, uint16_t properties, PHLWINDOW pIgnoreWindow) {
     const auto PMONITOR = getMonitorFromVector(pos);
     if (!PMONITOR)
         return nullptr;
@@ -905,8 +905,12 @@ PHLWINDOW CCompositor::vectorToWindowUnified(const Vector2D& pos, uint8_t proper
     static auto PBORDERGRABEXTEND    = CConfigValue<Hyprlang::INT>("general:extend_border_grab_area");
     static auto PSPECIALFALLTHRU     = CConfigValue<Hyprlang::INT>("input:special_fallthrough");
     static auto PMODALPARENTBLOCKING = CConfigValue<Hyprlang::INT>("general:modal_parent_blocking");
+    static auto PFOLLOWMOUSESHRINK   = CConfigValue<Hyprlang::INT>("input:follow_mouse_shrink");
     const auto  BORDER_GRAB_AREA     = *PRESIZEONBORDER ? *PBORDERSIZE + *PBORDERGRABEXTEND : 0;
     const bool  ONLY_PRIORITY        = properties & Desktop::View::FOCUS_PRIORITY;
+    const bool  FOLLOW_MOUSE_CHECK   = properties & Desktop::View::FOLLOW_MOUSE_CHECK;
+    const auto  HITBOX_SHRINK        = FOLLOW_MOUSE_CHECK ? *PFOLLOWMOUSESHRINK : 0;
+    const auto  LASTFOCUSED          = Desktop::focusState()->window();
 
     const auto  isShadowedByModal = [](PHLWINDOW w) -> bool {
         return *PMODALPARENTBLOCKING && w->m_xdgSurface && w->m_xdgSurface->m_toplevel && w->m_xdgSurface->m_toplevel->anyChildModal();
@@ -922,6 +926,8 @@ PHLWINDOW CCompositor::vectorToWindowUnified(const Vector2D& pos, uint8_t proper
                 w != pIgnoreWindow && !isShadowedByModal(w)) {
                 const auto BB  = w->getWindowBoxUnified(properties);
                 CBox       box = BB.copy().expand(!w->isX11OverrideRedirect() ? BORDER_GRAB_AREA : 0);
+                if (HITBOX_SHRINK > 0 && w != LASTFOCUSED)
+                    box = box.copy().expand(-HITBOX_SHRINK);
                 if (box.containsPoint(pos))
                     return w;
 
@@ -964,6 +970,8 @@ PHLWINDOW CCompositor::vectorToWindowUnified(const Vector2D& pos, uint8_t proper
 
                     const auto BB  = w->getWindowBoxUnified(properties);
                     CBox       box = BB.copy().expand(!w->isX11OverrideRedirect() ? BORDER_GRAB_AREA : 0);
+                    if (HITBOX_SHRINK > 0 && w != LASTFOCUSED)
+                        box = box.copy().expand(-HITBOX_SHRINK);
                     if (box.containsPoint(pos)) {
 
                         if (w->m_isX11 && w->isX11OverrideRedirect() && !w->m_xwaylandSurface->wantsFocus()) {
@@ -1095,6 +1103,8 @@ PHLWINDOW CCompositor::vectorToWindowUnified(const Vector2D& pos, uint8_t proper
                     if (isWindowCloseToWorkAreaEdge(Math::eDirection::DIRECTION_DOWN))
                         box.height += BORDER_GRAB_AREA;
                 }
+                if (HITBOX_SHRINK > 0 && w != LASTFOCUSED)
+                    box = box.copy().expand(-HITBOX_SHRINK);
                 if (box.containsPoint(pos))
                     return w;
             }
diff --git a/src/Compositor.hpp b/src/Compositor.hpp
index 96850407..fe9ed2e9 100644
--- a/src/Compositor.hpp
+++ b/src/Compositor.hpp
@@ -99,7 +99,7 @@ class CCompositor {
     PHLMONITOR             getMonitorFromVector(const Vector2D&);
     void                   removeWindowFromVectorSafe(PHLWINDOW);
     bool                   monitorExists(PHLMONITOR);
-    PHLWINDOW              vectorToWindowUnified(const Vector2D&, uint8_t properties, PHLWINDOW pIgnoreWindow = nullptr);
+    PHLWINDOW              vectorToWindowUnified(const Vector2D&, uint16_t properties, PHLWINDOW pIgnoreWindow = nullptr);
     SP<CWLSurfaceResource> vectorToLayerSurface(const Vector2D&, std::vector<PHLLSREF>*, Vector2D*, PHLLS*, bool aboveLockscreen = false);
     SP<CWLSurfaceResource> vectorToLayerPopupSurface(const Vector2D&, PHLMONITOR monitor, Vector2D*, PHLLS*);
     SP<CWLSurfaceResource> vectorWindowToSurface(const Vector2D&, PHLWINDOW, Vector2D& sl);
diff --git a/src/config/legacy/ConfigManager.cpp b/src/config/legacy/ConfigManager.cpp
index bfe8fef3..310d2710 100644
--- a/src/config/legacy/ConfigManager.cpp
+++ b/src/config/legacy/ConfigManager.cpp
@@ -684,6 +684,7 @@ CConfigManager::CConfigManager() {
     registerConfigVar("animations:workspace_wraparound", Hyprlang::INT{0});
 
     registerConfigVar("input:follow_mouse", Hyprlang::INT{1});
+    registerConfigVar("input:follow_mouse_shrink", Hyprlang::INT{0});
     registerConfigVar("input:follow_mouse_threshold", Hyprlang::FLOAT{0});
     registerConfigVar("input:focus_on_close", Hyprlang::INT{0});
     registerConfigVar("input:mouse_refocus", Hyprlang::INT{1});
diff --git a/src/config/supplementary/ConfigDescriptions.hpp b/src/config/supplementary/ConfigDescriptions.hpp
index de679b52..862cc1a9 100644
--- a/src/config/supplementary/ConfigDescriptions.hpp
+++ b/src/config/supplementary/ConfigDescriptions.hpp
@@ -640,6 +640,14 @@ namespace Config::Supplementary {
             .data        = SConfigOptionDescription::SRangeData{1, 0, 3},
         },
         SConfigOptionDescription{
+            .value = "input:follow_mouse_shrink",
+            .description =
+                "Shrinks the inactive window hitboxes used for focus detection by the specified number of pixels. This creates a dead zone in gaps between windows where "
+                "moving the cursor will not change focus. Works only with follow_mouse = 1.",
+            .type = CONFIG_OPTION_INT,
+            .data = SConfigOptionDescription::SRangeData{0, 0, 300},
+        },
+        SConfigOptionDescription{
             .value       = "input:follow_mouse_threshold",
             .description = "The smallest distance in logical pixels the mouse needs to travel for the window under it to get focused. Works only with follow_mouse = 1.",
             .type        = CONFIG_OPTION_FLOAT,
diff --git a/src/desktop/view/Window.hpp b/src/desktop/view/Window.hpp
index f69585e3..a72c626b 100644
--- a/src/desktop/view/Window.hpp
+++ b/src/desktop/view/Window.hpp
@@ -55,7 +55,7 @@ namespace Desktop::View {
         GROUP_DENY        = 1 << 7, // deny
     };
 
-    enum eGetWindowProperties : uint8_t {
+    enum eGetWindowProperties : uint16_t {
         WINDOW_ONLY              = 0,
         RESERVED_EXTENTS         = 1 << 0,
         INPUT_EXTENTS            = 1 << 1,
@@ -65,6 +65,7 @@ namespace Desktop::View {
         USE_PROP_TILED           = 1 << 5,
         SKIP_FULLSCREEN_PRIORITY = 1 << 6,
         FOCUS_PRIORITY           = 1 << 7,
+        FOLLOW_MOUSE_CHECK       = 1 << 8,
     };
 
     enum eSuppressEvents : uint8_t {
diff --git a/src/managers/input/InputManager.cpp b/src/managers/input/InputManager.cpp
index 95e7704a..c4df7c53 100644
--- a/src/managers/input/InputManager.cpp
+++ b/src/managers/input/InputManager.cpp
@@ -419,7 +419,8 @@ void CInputManager::mouseMoveUnified(uint32_t time, bool refocus, bool mouse, st
     PHLWINDOW  pWindowIdeal;
     const auto getWindowIdeal = [&]() -> const PHLWINDOW& {
         if (!windowIdealQueried) {
-            pWindowIdeal       = g_pCompositor->vectorToWindowUnified(mouseCoords, Desktop::View::RESERVED_EXTENTS | Desktop::View::INPUT_EXTENTS | Desktop::View::ALLOW_FLOATING);
+            pWindowIdeal = g_pCompositor->vectorToWindowUnified(
+                mouseCoords, Desktop::View::RESERVED_EXTENTS | Desktop::View::INPUT_EXTENTS | Desktop::View::ALLOW_FLOATING | Desktop::View::FOLLOW_MOUSE_CHECK);
             windowIdealQueried = true;
         }