Windows, Style: Added style.WindowBorderHoverPadding setting to configure inner/outer padding applied to hit-testing of windows borders.

Amend 3c7177c, 59f3c4f, ae7f833.
Could be latched inside windows to be multi-dpi friendly, but likely won't matter soon.

Author: ocornut

docs/CHANGELOG.txt

@@ -47,6 +47,9 @@ Other changes:
 
 - Fixed IsItemDeactivatedAfterEdit() signal being broken for Checkbox(),
   RadioButton(), Selectable(). Regression from 2025/01/13. (#8370)
+- Windows, Style: Added style.WindowBorderHoverPadding setting to configure
+  inner/outer padding applied to hit-testing of windows borders and detection
+  of hovered window.
 - InputTextWithHint(): Fixed buffer-overflow (luckily often with no visible effect)
   when a user callback modified the buffer contents in a way that altered the
   visibility of the preview/hint buffer. (#8368) [@m9710797, @ocornut]

imgui.cpp

@@ -1167,11 +1167,7 @@ CODE
 // When using CTRL+TAB (or Gamepad Square+L/R) we delay the visual a little in order to reduce visual noise doing a fast switch.
 static const float NAV_WINDOWING_HIGHLIGHT_DELAY            = 0.20f;    // Time before the highlight and screen dimming starts fading in
 static const float NAV_WINDOWING_LIST_APPEAR_DELAY          = 0.15f;    // Time before the window list starts to appear
-
 static const float NAV_ACTIVATE_HIGHLIGHT_TIMER             = 0.10f;    // Time to highlight an item activated by a shortcut.
-
-// Window resizing from edges (when io.ConfigWindowsResizeFromEdges = true and ImGuiBackendFlags_HasMouseCursors is set in io.BackendFlags by backend)
-static const float WINDOWS_HOVER_PADDING                    = 4.0f;     // Extend outside window for hovering/resizing (maxxed with TouchPadding) and inside windows for borders. Affect FindHoveredWindow().
 static const float WINDOWS_RESIZE_FROM_EDGES_FEEDBACK_TIMER = 0.04f;    // Reduce visual noise by only highlighting the border after a certain time.
 static const float WINDOWS_MOUSE_WHEEL_SCROLL_LOCK_TIMER    = 0.70f;    // Lock scrolled window (so it doesn't pick child windows that are scrolling through) for a certain time, unless mouse moved.
 
@@ -1318,6 +1314,7 @@ ImGuiStyle::ImGuiStyle()
     WindowPadding               = ImVec2(8,8);      // Padding within a window
     WindowRounding              = 0.0f;             // Radius of window corners rounding. Set to 0.0f to have rectangular windows. Large values tend to lead to variety of artifacts and are not recommended.
     WindowBorderSize            = 1.0f;             // Thickness of border around windows. Generally set to 0.0f or 1.0f. Other values not well tested.
+    WindowBorderHoverPadding    = 4.0f;             // Hit-testing extent outside/inside resizing border. Also extend determination of hovered window. Generally meaningfully larger than WindowBorderSize to make it easy to reach borders.
     WindowMinSize               = ImVec2(32,32);    // Minimum window size
     WindowTitleAlign            = ImVec2(0.0f,0.5f);// Alignment for title bar text
     WindowMenuButtonPosition    = ImGuiDir_Left;    // Position of the collapsing/docking button in the title bar (left/right). Defaults to ImGuiDir_Left.
@@ -1379,6 +1376,7 @@ void ImGuiStyle::ScaleAllSizes(float scale_factor)
     WindowPadding = ImTrunc(WindowPadding * scale_factor);
     WindowRounding = ImTrunc(WindowRounding * scale_factor);
     WindowMinSize = ImTrunc(WindowMinSize * scale_factor);
+    WindowBorderHoverPadding = ImTrunc(WindowBorderHoverPadding * scale_factor);
     ChildRounding = ImTrunc(ChildRounding * scale_factor);
     PopupRounding = ImTrunc(PopupRounding * scale_factor);
     FramePadding = ImTrunc(FramePadding * scale_factor);
@@ -5037,7 +5035,7 @@ void ImGui::UpdateHoveredWindowAndCaptureFlags()
 
     // FIXME-DPI: This storage was added on 2021/03/31 for test engine, but if we want to multiply WINDOWS_HOVER_PADDING
     // by DpiScale, we need to make this window-agnostic anyhow, maybe need storing inside ImGuiWindow.
-    g.WindowsHoverPadding = ImMax(g.Style.TouchExtraPadding, ImVec2(WINDOWS_HOVER_PADDING, WINDOWS_HOVER_PADDING));
+    g.WindowsBorderHoverPadding = ImMax(ImMax(g.Style.TouchExtraPadding.x, g.Style.TouchExtraPadding.y), g.Style.WindowBorderHoverPadding);
 
     // Find the window hovered by mouse:
     // - Child windows can extend beyond the limit of their parent so we need to derive HoveredRootWindow from HoveredWindow.
@@ -5800,7 +5798,7 @@ void ImGui::FindHoveredWindowEx(const ImVec2& pos, bool find_first_and_in_any_vi
         hovered_window = g.MovingWindow;
 
     ImVec2 padding_regular = g.Style.TouchExtraPadding;
-    ImVec2 padding_for_resize = g.IO.ConfigWindowsResizeFromEdges ? g.WindowsHoverPadding : padding_regular;
+    ImVec2 padding_for_resize = ImMax(g.Style.TouchExtraPadding, ImVec2(g.Style.WindowBorderHoverPadding, g.Style.WindowBorderHoverPadding));
     for (int i = g.Windows.Size - 1; i >= 0; i--)
     {
         ImGuiWindow* window = g.Windows[i];
@@ -6502,7 +6500,7 @@ static int ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& si
     int ret_auto_fit_mask = 0x00;
     const float grip_draw_size = IM_TRUNC(ImMax(g.FontSize * 1.35f, window->WindowRounding + 1.0f + g.FontSize * 0.2f));
     const float grip_hover_inner_size = (resize_grip_count > 0) ? IM_TRUNC(grip_draw_size * 0.75f) : 0.0f;
-    const float grip_hover_outer_size = g.IO.ConfigWindowsResizeFromEdges ? WINDOWS_HOVER_PADDING : 0.0f;
+    const float grip_hover_outer_size = g.WindowsBorderHoverPadding;
 
     ImRect clamp_rect = visibility_rect;
     const bool window_move_from_title_bar = g.IO.ConfigWindowsMoveFromTitleBarOnly && !(window->Flags & ImGuiWindowFlags_NoTitleBar);
@@ -6570,7 +6568,7 @@ static int ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& si
         const ImGuiAxis axis = (border_n == ImGuiDir_Left || border_n == ImGuiDir_Right) ? ImGuiAxis_X : ImGuiAxis_Y;
 
         bool hovered, held;
-        ImRect border_rect = GetResizeBorderRect(window, border_n, grip_hover_inner_size, WINDOWS_HOVER_PADDING);
+        ImRect border_rect = GetResizeBorderRect(window, border_n, grip_hover_inner_size, g.WindowsBorderHoverPadding);
         ImGuiID border_id = window->GetID(border_n + 4); // == GetWindowResizeBorderID()
         ItemAdd(border_rect, border_id, NULL, ImGuiItemFlags_NoNav);
         ButtonBehavior(border_rect, border_id, &hovered, &held, ImGuiButtonFlags_FlattenChildren | ImGuiButtonFlags_NoNavFocus);
@@ -6608,7 +6606,7 @@ static int ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& si
 
             const ImVec2 border_curr = (window->Pos + ImMin(def.SegmentN1, def.SegmentN2) * window->Size);
             const float border_target_rel_mode_for_axis = border_curr[axis] + g.IO.MouseDelta[axis];
-            const float border_target_abs_mode_for_axis = g.IO.MousePos[axis] - g.ActiveIdClickOffset[axis] + WINDOWS_HOVER_PADDING; // Match ButtonBehavior() padding above.
+            const float border_target_abs_mode_for_axis = g.IO.MousePos[axis] - g.ActiveIdClickOffset[axis] + g.WindowsBorderHoverPadding; // Match ButtonBehavior() padding above.
 
             // Use absolute mode position
             ImVec2 border_target = window->Pos;
@@ -6697,7 +6695,7 @@ static int ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& si
 
     // Recalculate next expected border expected coordinates
     if (*border_held != -1)
-        g.WindowResizeBorderExpectedRect = GetResizeBorderRect(window, *border_held, grip_hover_inner_size, WINDOWS_HOVER_PADDING);
+        g.WindowResizeBorderExpectedRect = GetResizeBorderRect(window, *border_held, grip_hover_inner_size, g.WindowsBorderHoverPadding);
 
     return ret_auto_fit_mask;
 }
@@ -10184,7 +10182,8 @@ static void ImGui::ErrorCheckNewFrameSanityChecks()
     IM_ASSERT(g.Style.CurveTessellationTol > 0.0f                       && "Invalid style setting!");
     IM_ASSERT(g.Style.CircleTessellationMaxError > 0.0f                 && "Invalid style setting!");
     IM_ASSERT(g.Style.Alpha >= 0.0f && g.Style.Alpha <= 1.0f            && "Invalid style setting!"); // Allows us to avoid a few clamps in color computations
-    IM_ASSERT(g.Style.WindowMinSize.x >= 1.0f && g.Style.WindowMinSize.y >= 1.0f && "Invalid style setting.");
+    IM_ASSERT(g.Style.WindowMinSize.x >= 1.0f && g.Style.WindowMinSize.y >= 1.0f && "Invalid style setting!");
+    IM_ASSERT(g.Style.WindowBorderHoverPadding > 0.0f                   && "Invalid style setting!"); // Required otherwise cannot resize from borders.
     IM_ASSERT(g.Style.WindowMenuButtonPosition == ImGuiDir_None || g.Style.WindowMenuButtonPosition == ImGuiDir_Left || g.Style.WindowMenuButtonPosition == ImGuiDir_Right);
     IM_ASSERT(g.Style.ColorButtonPosition == ImGuiDir_Left || g.Style.ColorButtonPosition == ImGuiDir_Right);
 

imgui.h

@@ -2146,6 +2146,7 @@ struct ImGuiStyle
     ImVec2      WindowPadding;              // Padding within a window.
     float       WindowRounding;             // Radius of window corners rounding. Set to 0.0f to have rectangular windows. Large values tend to lead to variety of artifacts and are not recommended.
     float       WindowBorderSize;           // Thickness of border around windows. Generally set to 0.0f or 1.0f. (Other values are not well tested and more CPU/GPU costly).
+    float       WindowBorderHoverPadding;   // Hit-testing extent outside/inside resizing border. Also extend determination of hovered window. Generally meaningfully larger than WindowBorderSize to make it easy to reach borders.
     ImVec2      WindowMinSize;              // Minimum window size. This is a global setting. If you want to constrain individual windows, use SetNextWindowSizeConstraints().
     ImVec2      WindowTitleAlign;           // Alignment for title bar text. Defaults to (0.0f,0.5f) for left-aligned,vertically centered.
     ImGuiDir    WindowMenuButtonPosition;   // Side of the collapsing/docking button in the title bar (None/Left/Right). Defaults to ImGuiDir_Left.

imgui_demo.cpp

@@ -7985,11 +7985,14 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
             ImGui::SliderAngle("TableAngledHeadersAngle", &style.TableAngledHeadersAngle, -50.0f, +50.0f);
             ImGui::SliderFloat2("TableAngledHeadersTextAlign", (float*)&style.TableAngledHeadersTextAlign, 0.0f, 1.0f, "%.2f");
 
-            ImGui::SeparatorText("Widgets");
+            ImGui::SeparatorText("Windows");
             ImGui::SliderFloat2("WindowTitleAlign", (float*)&style.WindowTitleAlign, 0.0f, 1.0f, "%.2f");
+            ImGui::SliderFloat("WindowBorderHoverPadding", &style.WindowBorderHoverPadding, 1.0f, 20.0f, "%.0f");
             int window_menu_button_position = style.WindowMenuButtonPosition + 1;
             if (ImGui::Combo("WindowMenuButtonPosition", (int*)&window_menu_button_position, "None\0Left\0Right\0"))
                 style.WindowMenuButtonPosition = (ImGuiDir)(window_menu_button_position - 1);
+
+            ImGui::SeparatorText("Widgets");
             ImGui::Combo("ColorButtonPosition", (int*)&style.ColorButtonPosition, "Left\0Right\0");
             ImGui::SliderFloat2("ButtonTextAlign", (float*)&style.ButtonTextAlign, 0.0f, 1.0f, "%.2f");
             ImGui::SameLine(); HelpMarker("Alignment applies when a button is larger than its text content.");

imgui_internal.h

@@ -2083,7 +2083,7 @@ struct ImGuiContext
     ImVector<ImGuiWindowStackData> CurrentWindowStack;
     ImGuiStorage            WindowsById;                        // Map window's ImGuiID to ImGuiWindow*
     int                     WindowsActiveCount;                 // Number of unique windows submitted by frame
-    ImVec2                  WindowsHoverPadding;                // Padding around resizable windows for which hovering on counts as hovering the window == ImMax(style.TouchExtraPadding, WINDOWS_HOVER_PADDING).
+    float                   WindowsBorderHoverPadding;          // Padding around resizable windows for which hovering on counts as hovering the window == ImMax(style.TouchExtraPadding, style.WindowBorderHoverPadding). This isn't so multi-dpi friendly.
     ImGuiID                 DebugBreakInWindow;                 // Set to break in Begin() call.
     ImGuiWindow*            CurrentWindow;                      // Window being drawn into
     ImGuiWindow*            HoveredWindow;                      // Window the mouse is hovering. Will typically catch mouse inputs.