Viewport: Fixed DPI changing viewport from interfering with moving another window (disabling code) + metrics crash fix on closed viewport window + Windows 10 call to SetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) for DPI, with no noticeable improvements. (#1542, #1676)

examples/imgui_impl_win32.cpp

@@ -286,9 +286,7 @@ IMGUI_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARAM wPa
 // So we dynamically select and load those functions to avoid dependencies. This is the scheme successfully 
 // used by GLFW (from which we borrowed some of the code here) and other applications aiming to be portable.
 //---------------------------------------------------------------------------------------------------------
-// FIXME-DPI: For now we just call SetProcessDpiAwareness(PROCESS_PER_MONITOR_AWARE) without requiring SDK 8.1 or 10.
-// We may allow/aim calling the most-recent-available version, e.g. Windows 10 Creators Update has SetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
-// At this point ImGui_ImplWin32_EnableDpiAwareness() is just a helper called by main.cpp, we don't call it ourselves.
+// At this point ImGui_ImplWin32_EnableDpiAwareness() is just a helper called by main.cpp, we don't call it automatically.
 //---------------------------------------------------------------------------------------------------------
 
 static BOOL IsWindowsVersionOrGreater(WORD major, WORD minor, WORD sp)
@@ -307,11 +305,26 @@ static BOOL IsWindowsVersionOrGreater(WORD major, WORD minor, WORD sp)
 typedef enum { PROCESS_DPI_UNAWARE = 0, PROCESS_SYSTEM_DPI_AWARE = 1, PROCESS_PER_MONITOR_DPI_AWARE = 2 } PROCESS_DPI_AWARENESS;
 typedef enum { MDT_EFFECTIVE_DPI = 0, MDT_ANGULAR_DPI = 1, MDT_RAW_DPI = 2, MDT_DEFAULT = MDT_EFFECTIVE_DPI } MONITOR_DPI_TYPE;
 #endif
-typedef HRESULT(WINAPI * PFN_SetProcessDpiAwareness)(PROCESS_DPI_AWARENESS);              // Shcore.lib+dll, Windows 8.1
-typedef HRESULT(WINAPI * PFN_GetDpiForMonitor)(HMONITOR, MONITOR_DPI_TYPE, UINT*, UINT*); // Shcore.lib+dll, Windows 8.1
+#ifndef _DPI_AWARENESS_CONTEXTS_
+DECLARE_HANDLE(DPI_AWARENESS_CONTEXT);
+#define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE    (DPI_AWARENESS_CONTEXT)-3
+#define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 (DPI_AWARENESS_CONTEXT)-4
+#endif
+typedef HRESULT(WINAPI * PFN_SetProcessDpiAwareness)(PROCESS_DPI_AWARENESS);                     // Shcore.lib+dll, Windows 8.1
+typedef HRESULT(WINAPI * PFN_GetDpiForMonitor)(HMONITOR, MONITOR_DPI_TYPE, UINT*, UINT*);        // Shcore.lib+dll, Windows 8.1
+typedef DPI_AWARENESS_CONTEXT(WINAPI * PFN_SetThreadDpiAwarenessContext)(DPI_AWARENESS_CONTEXT); // User32.lib+dll, Windows 10 v1607 (Creators Update)
 
 void ImGui_ImplWin32_EnableDpiAwareness()
 {
+    // if (IsWindows10OrGreater()) // FIXME-DPI: This needs a manifest to succeed. Instead we try to grab the function pointer.
+    {
+        static HINSTANCE user32_dll = ::LoadLibraryA("user32.dll"); // Reference counted per-process
+        if (PFN_SetThreadDpiAwarenessContext SetThreadDpiAwarenessContextFn = (PFN_SetThreadDpiAwarenessContext)::GetProcAddress(user32_dll, "SetThreadDpiAwarenessContext"))
+        {
+            SetThreadDpiAwarenessContextFn(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
+            return;
+        }
+    }
     if (IsWindows8Point1OrGreater())
     {
         static HINSTANCE shcore_dll = ::LoadLibraryA("shcore.dll"); // Reference counted per-process

imgui.cpp

@@ -14035,8 +14035,11 @@ void ImGui::ScaleWindowsInViewport(ImGuiViewportP* viewport, float scale)
 {
     ImGuiContext& g = *GImGui;
 
-    if (g.MovingWindow != NULL)
-        g.ActiveIdClickOffset = ImFloor(g.ActiveIdClickOffset * scale);
+    // FIXME-DPI: This is meant to have the window rescale around the mouse. It currently creates feedback loop when a window is straddling a DPI transition border.
+    // NB: since our sizes do not perfectly linearly scale, deferring the ClickOffset scale until we know the actual window scale ratio may get us slightly more precise mouse positioning.
+    //if (g.MovingWindow != NULL && g.MovingWindow->Viewport == viewport)
+    //    g.ActiveIdClickOffset = ImFloor(g.ActiveIdClickOffset * scale);
+
     /*
     if (g.IO.MousePosViewport == viewport->ID)
     {
@@ -14106,8 +14109,8 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                     return;
                 }
 
-                ImDrawList* overlay_draw_list = GetOverlayDrawList(viewport); // Render additional visuals into the top-most draw list
-                if (window && ImGui::IsItemHovered())
+                ImDrawList* overlay_draw_list = viewport ? GetOverlayDrawList(viewport) : NULL; // Render additional visuals into the top-most draw list
+                if (window && overlay_draw_list && ImGui::IsItemHovered())
                     overlay_draw_list->AddRect(window->Pos, window->Pos + window->Size, IM_COL32(255, 255, 0, 255));
                 if (!node_open)
                     return;
@@ -14124,7 +14127,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                     }
                     ImDrawIdx* idx_buffer = (draw_list->IdxBuffer.Size > 0) ? draw_list->IdxBuffer.Data : NULL;
                     bool pcmd_node_open = ImGui::TreeNode((void*)(pcmd - draw_list->CmdBuffer.begin()), "Draw %4d %s vtx, tex 0x%p, clip_rect (%4.0f,%4.0f)-(%4.0f,%4.0f)", pcmd->ElemCount, draw_list->IdxBuffer.Size > 0 ? "indexed" : "non-indexed", pcmd->TextureId, pcmd->ClipRect.x, pcmd->ClipRect.y, pcmd->ClipRect.z, pcmd->ClipRect.w);
-                    if (show_clip_rects && ImGui::IsItemHovered())
+                    if (show_clip_rects && overlay_draw_list && ImGui::IsItemHovered())
                     {
                         ImRect clip_rect = pcmd->ClipRect;
                         ImRect vtxs_rect;
@@ -14151,7 +14154,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                                 buf_p += ImFormatString(buf_p, (int)(buf_end - buf_p), "%s %04d: pos (%8.2f,%8.2f), uv (%.6f,%.6f), col %08X\n", (n == 0) ? "vtx" : "   ", vtx_i, v.pos.x, v.pos.y, v.uv.x, v.uv.y, v.col);
                             }
                             ImGui::Selectable(buf, false);
-                            if (ImGui::IsItemHovered())
+                            if (overlay_draw_list && ImGui::IsItemHovered())
                             {
                                 ImDrawListFlags backup_flags = overlay_draw_list->Flags;
                                 overlay_draw_list->Flags &= ~ImDrawListFlags_AntiAliasedLines; // Disable AA on triangle outlines at is more readable for very large and thin triangles.