Combo: display popup above if there's isn't enough space below / or select largest side (#505)

imgui.cpp

@@ -8093,8 +8093,15 @@ bool ImGui::Combo(const char* label, int* current_item, bool (*items_getter)(voi
             height_in_items = 7;
 
         float popup_height = (label_size.y + style.ItemSpacing.y) * ImMin(items_count, height_in_items) + (style.FramePadding.y * 3);
-        ImRect popup_rect(ImVec2(frame_bb.Min.x, frame_bb.Max.y), ImVec2(frame_bb.Max.x, frame_bb.Max.y + popup_height));
-        popup_rect.Max.y = ImMin(popup_rect.Max.y, g.IO.DisplaySize.y - style.DisplaySafeAreaPadding.y); // Adhoc height limit for Combo. Ideally should be handled in Begin() along with other popups size, we want to have the possibility of moving the popup above as well.
+        float popup_y1 = frame_bb.Max.y;
+        float popup_y2 = ImClamp(popup_y1 + popup_height, popup_y1, g.IO.DisplaySize.y - style.DisplaySafeAreaPadding.y);
+        if ((popup_y2 - popup_y1) < ImMin(popup_height, frame_bb.Min.y - style.DisplaySafeAreaPadding.y))
+        {
+            // Position our combo ABOVE because there's more space to fit! (FIXME: Handle in Begin() or use a shared helper. We have similar code in Begin() for popup placement)
+            popup_y1 = ImClamp(frame_bb.Min.y - popup_height, style.DisplaySafeAreaPadding.y, frame_bb.Min.y);
+            popup_y2 = frame_bb.Min.y;
+        }
+        ImRect popup_rect(ImVec2(frame_bb.Min.x, popup_y1), ImVec2(frame_bb.Max.x, popup_y2));
         ImGui::SetNextWindowPos(popup_rect.Min);
         ImGui::SetNextWindowSize(popup_rect.GetSize());
         ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, style.FramePadding);