Added SetNextWindowPosCenter() (#249)

imgui.cpp

@@ -3562,12 +3562,16 @@ bool ImGui::Begin(const char* name, bool* p_opened, const ImVec2& size_on_first_
 
     // Process SetNextWindow***() calls
     bool window_pos_set_by_api = false, window_size_set_by_api = false;
+    bool window_pos_center = false;
     if (g.SetNextWindowPosCond)
     {
         const ImVec2 backup_cursor_pos = window->DC.CursorPos;                  // FIXME: not sure of the exact reason of this anymore :( need to look into that.
         if (!window_was_visible) window->SetWindowPosAllowFlags |= ImGuiSetCond_Appearing;
         window_pos_set_by_api = (window->SetWindowPosAllowFlags & g.SetNextWindowPosCond) != 0;
-        ImGui::SetWindowPos(g.SetNextWindowPosVal, g.SetNextWindowPosCond);
+        if (window_pos_set_by_api && ImLengthSqr(g.SetNextWindowPosVal - ImVec2(-FLT_MAX,-FLT_MAX)) < 0.001f)
+            window_pos_center = true;
+        else
+            ImGui::SetWindowPos(g.SetNextWindowPosVal, g.SetNextWindowPosCond);
         window->DC.CursorPos = backup_cursor_pos;
         g.SetNextWindowPosCond = 0;
     }
@@ -3735,7 +3739,15 @@ bool ImGui::Begin(const char* name, bool* p_opened, const ImVec2& size_on_first_
         }
 
         // Position popup
-        if (flags & ImGuiWindowFlags_ChildMenu)
+        if ((flags & ImGuiWindowFlags_Modal) && !window_pos_set_by_api && window_appearing_after_being_hidden)
+            window_pos_center = true;
+
+        if (window_pos_center)
+        {
+            ImRect fullscreen_rect(GetVisibleRect());
+            SetWindowPos(ImMax(style.DisplaySafeAreaPadding, fullscreen_rect.GetCenter() - window->SizeFull * 0.5f));
+        }
+        else if (flags & ImGuiWindowFlags_ChildMenu)
         {
             IM_ASSERT(window_pos_set_by_api);
             ImRect rect_to_avoid;
@@ -3747,18 +3759,8 @@ bool ImGui::Begin(const char* name, bool* p_opened, const ImVec2& size_on_first_
         }
         else if ((flags & ImGuiWindowFlags_Popup) != 0 && !window_pos_set_by_api && window_appearing_after_being_hidden)
         {
-            if (flags & ImGuiWindowFlags_Modal)
-            {
-                // Center
-                // FIXME: Should be widely available, e.g. via SetNextWindowPos() API etc.
-                ImRect fullscreen_rect(GetVisibleRect());
-                window->PosFloat = ImMax(style.DisplaySafeAreaPadding, fullscreen_rect.GetCenter() - window->SizeContents * 0.5f);
-            }
-            else
-            {
-                ImRect rect_to_avoid(window->PosFloat.x - 1, window->PosFloat.y - 1, window->PosFloat.x + 1, window->PosFloat.y + 1);
-                window->PosFloat = FindBestWindowPos(window->PosFloat, window->Size, flags, &window->AutoPosLastDirection, rect_to_avoid);
-            }
+            ImRect rect_to_avoid(window->PosFloat.x - 1, window->PosFloat.y - 1, window->PosFloat.x + 1, window->PosFloat.y + 1);
+            window->PosFloat = FindBestWindowPos(window->PosFloat, window->Size, flags, &window->AutoPosLastDirection, rect_to_avoid);
         }
 
         // Position tooltip (always follows mouse)
@@ -4601,6 +4603,13 @@ void ImGui::SetNextWindowPos(const ImVec2& pos, ImGuiSetCond cond)
     g.SetNextWindowPosCond = cond ? cond : ImGuiSetCond_Always;
 }
 
+void ImGui::SetNextWindowPosCenter(ImGuiSetCond cond)
+{
+    ImGuiState& g = *GImGui;
+    g.SetNextWindowPosVal = ImVec2(-FLT_MAX, -FLT_MAX);
+    g.SetNextWindowPosCond = cond ? cond : ImGuiSetCond_Always;
+}
+
 void ImGui::SetNextWindowSize(const ImVec2& size, ImGuiSetCond cond)
 {
     ImGuiState& g = *GImGui;

imgui.h

@@ -122,10 +122,11 @@ namespace ImGui
     IMGUI_API float         GetWindowWidth();
     IMGUI_API bool          IsWindowCollapsed();
 
-    IMGUI_API void          SetNextWindowPos(const ImVec2& pos, ImGuiSetCond cond = 0);         // set next window position - call before Begin()
-    IMGUI_API void          SetNextWindowSize(const ImVec2& size, ImGuiSetCond cond = 0);       // set next window size. set to ImVec2(0,0) to force an auto-fit
-    IMGUI_API void          SetNextWindowCollapsed(bool collapsed, ImGuiSetCond cond = 0);      // set next window collapsed state
-    IMGUI_API void          SetNextWindowFocus();                                               // set next window to be focused / front-most
+    IMGUI_API void          SetNextWindowPos(const ImVec2& pos, ImGuiSetCond cond = 0);         // set next window position. call before Begin()
+    IMGUI_API void          SetNextWindowPosCenter(ImGuiSetCond cond = 0);                      // set next window position to be centered on screen. call before Begin()
+    IMGUI_API void          SetNextWindowSize(const ImVec2& size, ImGuiSetCond cond = 0);       // set next window size. set to ImVec2(0,0) to force an auto-fit. call before Begin()
+    IMGUI_API void          SetNextWindowCollapsed(bool collapsed, ImGuiSetCond cond = 0);      // set next window collapsed state. call before Begin()
+    IMGUI_API void          SetNextWindowFocus();                                               // set next window to be focused / front-most. call before Begin()
     IMGUI_API void          SetWindowPos(const ImVec2& pos, ImGuiSetCond cond = 0);             // set current window position - call within Begin()/End(). may incur tearing
     IMGUI_API void          SetWindowSize(const ImVec2& size, ImGuiSetCond cond = 0);           // set current window size. set to ImVec2(0,0) to force an auto-fit. may incur tearing
     IMGUI_API void          SetWindowCollapsed(bool collapsed, ImGuiSetCond cond = 0);          // set current window collapsed state