[UI] Capture mouse.

src/xenia/ui/imgui_drawer.cc

@@ -268,16 +268,27 @@ void ImGuiDrawer::OnKeyChar(KeyEvent* e) {
 void ImGuiDrawer::OnMouseDown(MouseEvent* e) {
   auto& io = GetIO();
   io.MousePos = ImVec2(float(e->x()), float(e->y()));
+  int button = -1;
   switch (e->button()) {
     case xe::ui::MouseEvent::Button::kLeft: {
-      io.MouseDown[0] = true;
-    } break;
+      button = 0;
+      break;
+    }
     case xe::ui::MouseEvent::Button::kRight: {
-      io.MouseDown[1] = true;
-    } break;
+      button = 1;
+      break;
+    }
     default: {
       // Ignored.
-    } break;
+      break;
+    }
+  }
+
+  if (button >= 0 && button < std::size(io.MouseDown)) {
+    if (!ImGui::IsAnyMouseDown()) {
+      window_->CaptureMouse();
+    }
+    io.MouseDown[button] = true;
   }
 }
 
@@ -289,16 +300,27 @@ void ImGuiDrawer::OnMouseMove(MouseEvent* e) {
 void ImGuiDrawer::OnMouseUp(MouseEvent* e) {
   auto& io = GetIO();
   io.MousePos = ImVec2(float(e->x()), float(e->y()));
+  int button = -1;
   switch (e->button()) {
     case xe::ui::MouseEvent::Button::kLeft: {
-      io.MouseDown[0] = false;
-    } break;
+      button = 0;
+      break;
+    }
     case xe::ui::MouseEvent::Button::kRight: {
-      io.MouseDown[1] = false;
-    } break;
+      button = 1;
+      break;
+    }
     default: {
       // Ignored.
-    } break;
+      break;
+    }
+  }
+
+  if (button >= 0 && button < std::size(io.MouseDown)) {
+    io.MouseDown[button] = false;
+    if (!ImGui::IsAnyMouseDown()) {
+      window_->ReleaseMouse();
+    }
   }
 }
 

src/xenia/ui/window.h

@@ -59,6 +59,9 @@ class Window {
   virtual bool SetIcon(const void* buffer, size_t size) = 0;
   void ResetIcon() { SetIcon(nullptr, 0); }
 
+  virtual bool CaptureMouse() = 0;
+  virtual bool ReleaseMouse() = 0;
+
   virtual bool is_fullscreen() const { return false; }
   virtual void ToggleFullscreen(bool fullscreen) {}
 

src/xenia/ui/window_gtk.h

@@ -42,6 +42,10 @@ class GTKWindow : public Window {
 
   bool SetIcon(const void* buffer, size_t size) override;
 
+  // This seems to happen implicitly compared to Windows.
+  bool CaptureMouse() override { return true; };
+  bool ReleaseMouse() override { return true; };
+
   bool is_fullscreen() const override;
   void ToggleFullscreen(bool fullscreen) override;
 

src/xenia/ui/window_win.cc

@@ -236,6 +236,21 @@ bool Win32Window::SetIcon(const void* buffer, size_t size) {
   return false;
 }
 
+bool Win32Window::CaptureMouse() {
+  if (GetCapture() != nullptr) {
+    return false;
+  }
+  SetCapture(hwnd_);
+  return true;
+}
+
+bool Win32Window::ReleaseMouse() {
+  if (GetCapture() != hwnd_) {
+    return false;
+  }
+  return ReleaseCapture() != 0;
+}
+
 bool Win32Window::is_fullscreen() const { return fullscreen_; }
 
 // https://blogs.msdn.microsoft.com/oldnewthing/20131017-00/?p=2903

src/xenia/ui/window_win.h

@@ -38,6 +38,9 @@ class Win32Window : public Window {
 
   bool SetIcon(const void* buffer, size_t size) override;
 
+  bool CaptureMouse() override;
+  bool ReleaseMouse() override;
+
   bool is_fullscreen() const override;
   void ToggleFullscreen(bool fullscreen) override;