Viewports: added platform_io.Platform_GetWindowWorkAreaInsets() hook. (#7823)

docs/CHANGELOG.txt

@@ -52,6 +52,10 @@ Other changes:
 - Examples: GLFW (all), SDL2 (all), SDL3 (all), Win32+OpenGL3: rework examples main loop
   to handle minimization without burning CPU or GPU by running unthrottled code. (#7844)
 
+Docking+Viewports Branch:
+
+- Viewports: added optional platform_io.Platform_GetWindowWorkAreaInsets() hook
+  to allow backends to alter the default per-viewport work-area. (#7823)
 
 
 -----------------------------------------------------------------------

imgui.cpp

@@ -15238,11 +15238,18 @@ static void ImGui::UpdateViewportsNewFrame()
         // Update/copy monitor info
         UpdateViewportPlatformMonitor(viewport);
 
-        // Lock down space taken by menu bars and status bars
+        // Lock down space taken by menu bars and status bars + query initial insets from backend
         // Setup initial value for functions like BeginMainMenuBar(), DockSpaceOverViewport() etc.
         viewport->WorkInsetMin = viewport->BuildWorkInsetMin;
         viewport->WorkInsetMax = viewport->BuildWorkInsetMax;
         viewport->BuildWorkInsetMin = viewport->BuildWorkInsetMax = ImVec2(0.0f, 0.0f);
+        if (g.PlatformIO.Platform_GetWindowWorkAreaInsets != NULL)
+        {
+            ImVec4 insets = g.PlatformIO.Platform_GetWindowWorkAreaInsets(viewport);
+            IM_ASSERT(insets.x >= 0.0f && insets.y >= 0.0f && insets.z >= 0.0f && insets.w >= 0.0f);
+            viewport->BuildWorkInsetMin = ImVec2(insets.x, insets.y);
+            viewport->BuildWorkInsetMax = ImVec2(insets.z, insets.w);
+        }
         viewport->UpdateWorkRect();
 
         // Reset alpha every frame. Users of transparency (docking) needs to request a lower alpha back.

imgui.h

@@ -3706,6 +3706,7 @@ struct ImGuiPlatformIO
     void    (*Platform_SwapBuffers)(ImGuiViewport* vp, void* render_arg);   // . . . R .  // (Optional) Call Present/SwapBuffers (platform side! This is often unused!). 'render_arg' is the value passed to RenderPlatformWindowsDefault().
     float   (*Platform_GetWindowDpiScale)(ImGuiViewport* vp);               // N . . . .  // (Optional) [BETA] FIXME-DPI: DPI handling: Return DPI scale for this viewport. 1.0f = 96 DPI.
     void    (*Platform_OnChangedViewport)(ImGuiViewport* vp);               // . F . . .  // (Optional) [BETA] FIXME-DPI: DPI handling: Called during Begin() every time the viewport we are outputting into changes, so backend has a chance to swap fonts to adjust style.
+    ImVec4  (*Platform_GetWindowWorkAreaInsets)(ImGuiViewport* vp);         // N . . . .  // (Optional) [BETA] Get initial work area inset for the viewport (won't be covered by main menu bar, dockspace over viewport etc.). Default to (0,0),(0,0). 'safeAreaInsets' in iOS land, 'DisplayCutout' in Android land.
     int     (*Platform_CreateVkSurface)(ImGuiViewport* vp, ImU64 vk_inst, const void* vk_allocators, ImU64* out_vk_surface); // (Optional) For a Vulkan Renderer to call into Platform code (since the surface creation needs to tie them both).
 
     // (Optional) Renderer functions (e.g. DirectX, OpenGL, Vulkan)

imgui_internal.h

@@ -1990,6 +1990,7 @@ struct ImGuiViewportP : public ImGuiViewport
     // Per-viewport work area
     // - Insets are >= 0.0f values, distance from viewport corners to work area.
     // - BeginMainMenuBar() and DockspaceOverViewport() tend to use work area to avoid stepping over existing contents.
+    // - Generally 'safeAreaInsets' in iOS land, 'DisplayCutout' in Android land.
     ImVec2              WorkInsetMin;           // Work Area inset locked for the frame. GetWorkRect() always fits within GetMainRect().
     ImVec2              WorkInsetMax;           // "
     ImVec2              BuildWorkInsetMin;      // Work Area inset accumulator for current frame, to become next frame's WorkInset