Internals: Combo: Extracted into a BeginComboPopup() function. (#4168)

Renamed frame_bb > bb locally.

imgui_internal.h

@@ -2401,6 +2401,9 @@ namespace ImGui
     IMGUI_API ImVec2        FindBestWindowPosForPopupEx(const ImVec2& ref_pos, const ImVec2& size, ImGuiDir* last_dir, const ImRect& r_outer, const ImRect& r_avoid, ImGuiPopupPositionPolicy policy);
     IMGUI_API bool          BeginViewportSideBar(const char* name, ImGuiViewport* viewport, ImGuiDir dir, float size, ImGuiWindowFlags window_flags);
 
+    // Combos
+    IMGUI_API bool          BeginComboPopup(ImGuiID popup_id, const ImRect& bb, ImGuiComboFlags flags);
+
     // Gamepad/Keyboard Navigation
     IMGUI_API void          NavInitWindow(ImGuiWindow* window, bool force_reinit);
     IMGUI_API bool          NavMoveRequestButNoResultYet();

imgui_widgets.cpp

@@ -1537,7 +1537,9 @@ void ImGui::ShrinkWidths(ImGuiShrinkWidthItem* items, int count, float width_exc
 //-------------------------------------------------------------------------
 // [SECTION] Widgets: ComboBox
 //-------------------------------------------------------------------------
+// - CalcMaxPopupHeightFromItemCount() [Internal]
 // - BeginCombo()
+// - BeginComboPopup() [Internal]
 // - EndCombo()
 // - Combo()
 //-------------------------------------------------------------------------
@@ -1552,78 +1554,91 @@ static float CalcMaxPopupHeightFromItemCount(int items_count)
 
 bool ImGui::BeginCombo(const char* label, const char* preview_value, ImGuiComboFlags flags)
 {
-    // Always consume the SetNextWindowSizeConstraint() call in our early return paths
     ImGuiContext& g = *GImGui;
-    bool has_window_size_constraint = (g.NextWindowData.Flags & ImGuiNextWindowDataFlags_HasSizeConstraint) != 0;
-    g.NextWindowData.Flags &= ~ImGuiNextWindowDataFlags_HasSizeConstraint;
-
     ImGuiWindow* window = GetCurrentWindow();
+
+    ImGuiNextWindowDataFlags backup_next_window_data_flags = g.NextWindowData.Flags;
+    g.NextWindowData.ClearFlags(); // We behave like Begin() and need to consume those values
     if (window->SkipItems)
         return false;
 
-    IM_ASSERT((flags & (ImGuiComboFlags_NoArrowButton | ImGuiComboFlags_NoPreview)) != (ImGuiComboFlags_NoArrowButton | ImGuiComboFlags_NoPreview)); // Can't use both flags together
-
     const ImGuiStyle& style = g.Style;
     const ImGuiID id = window->GetID(label);
+    IM_ASSERT((flags & (ImGuiComboFlags_NoArrowButton | ImGuiComboFlags_NoPreview)) != (ImGuiComboFlags_NoArrowButton | ImGuiComboFlags_NoPreview)); // Can't use both flags together
 
     const float arrow_size = (flags & ImGuiComboFlags_NoArrowButton) ? 0.0f : GetFrameHeight();
     const ImVec2 label_size = CalcTextSize(label, NULL, true);
     const float w = (flags & ImGuiComboFlags_NoPreview) ? arrow_size : CalcItemWidth();
-    const ImRect frame_bb(window->DC.CursorPos, window->DC.CursorPos + ImVec2(w, label_size.y + style.FramePadding.y * 2.0f));
+    const ImRect bb(window->DC.CursorPos, window->DC.CursorPos + ImVec2(w, label_size.y + style.FramePadding.y * 2.0f));
-    const ImRect total_bb(frame_bb.Min, frame_bb.Max + ImVec2(label_size.x > 0.0f ? style.ItemInnerSpacing.x + label_size.x : 0.0f, 0.0f));
+    const ImRect total_bb(bb.Min, bb.Max + ImVec2(label_size.x > 0.0f ? style.ItemInnerSpacing.x + label_size.x : 0.0f, 0.0f));
     ItemSize(total_bb, style.FramePadding.y);
-    if (!ItemAdd(total_bb, id, &frame_bb))
+    if (!ItemAdd(total_bb, id, &bb))
         return false;
 
+    // Open on click
     bool hovered, held;
-    bool pressed = ButtonBehavior(frame_bb, id, &hovered, &held);
+    bool pressed = ButtonBehavior(bb, id, &hovered, &held);
-
     const ImGuiID popup_id = ImHashStr("##ComboPopup", 0, id);
     bool popup_open = IsPopupOpen(popup_id, ImGuiPopupFlags_None);
+    if ((pressed || g.NavActivateId == id) && !popup_open)
+    {
+        OpenPopupEx(popup_id, ImGuiPopupFlags_None);
+        popup_open = true;
+    }
 
+    // Render shape
     const ImU32 frame_col = GetColorU32(hovered ? ImGuiCol_FrameBgHovered : ImGuiCol_FrameBg);
-    const float value_x2 = ImMax(frame_bb.Min.x, frame_bb.Max.x - arrow_size);
+    const float value_x2 = ImMax(bb.Min.x, bb.Max.x - arrow_size);
-    RenderNavHighlight(frame_bb, id);
+    RenderNavHighlight(bb, id);
     if (!(flags & ImGuiComboFlags_NoPreview))
-        window->DrawList->AddRectFilled(frame_bb.Min, ImVec2(value_x2, frame_bb.Max.y), frame_col, style.FrameRounding, (flags & ImGuiComboFlags_NoArrowButton) ? ImDrawFlags_RoundCornersAll : ImDrawFlags_RoundCornersLeft);
+        window->DrawList->AddRectFilled(bb.Min, ImVec2(value_x2, bb.Max.y), frame_col, style.FrameRounding, (flags & ImGuiComboFlags_NoArrowButton) ? ImDrawFlags_RoundCornersAll : ImDrawFlags_RoundCornersLeft);
     if (!(flags & ImGuiComboFlags_NoArrowButton))
     {
         ImU32 bg_col = GetColorU32((popup_open || hovered) ? ImGuiCol_ButtonHovered : ImGuiCol_Button);
         ImU32 text_col = GetColorU32(ImGuiCol_Text);
-        window->DrawList->AddRectFilled(ImVec2(value_x2, frame_bb.Min.y), frame_bb.Max, bg_col, style.FrameRounding, (w <= arrow_size) ? ImDrawFlags_RoundCornersAll : ImDrawFlags_RoundCornersRight);
+        window->DrawList->AddRectFilled(ImVec2(value_x2, bb.Min.y), bb.Max, bg_col, style.FrameRounding, (w <= arrow_size) ? ImDrawFlags_RoundCornersAll : ImDrawFlags_RoundCornersRight);
-        if (value_x2 + arrow_size - style.FramePadding.x <= frame_bb.Max.x)
+        if (value_x2 + arrow_size - style.FramePadding.x <= bb.Max.x)
-            RenderArrow(window->DrawList, ImVec2(value_x2 + style.FramePadding.y, frame_bb.Min.y + style.FramePadding.y), text_col, ImGuiDir_Down, 1.0f);
+            RenderArrow(window->DrawList, ImVec2(value_x2 + style.FramePadding.y, bb.Min.y + style.FramePadding.y), text_col, ImGuiDir_Down, 1.0f);
     }
-    RenderFrameBorder(frame_bb.Min, frame_bb.Max, style.FrameRounding);
+    RenderFrameBorder(bb.Min, bb.Max, style.FrameRounding);
+
+    // Render preview and label
     if (preview_value != NULL && !(flags & ImGuiComboFlags_NoPreview))
     {
-        ImVec2 preview_pos = frame_bb.Min + style.FramePadding;
         if (g.LogEnabled)
             LogSetNextTextDecoration("{", "}");
-        RenderTextClipped(preview_pos, ImVec2(value_x2, frame_bb.Max.y), preview_value, NULL, NULL, ImVec2(0.0f, 0.0f));
+        RenderTextClipped(bb.Min + style.FramePadding, ImVec2(value_x2, bb.Max.y), preview_value, NULL, NULL);
     }
     if (label_size.x > 0)
-        RenderText(ImVec2(frame_bb.Max.x + style.ItemInnerSpacing.x, frame_bb.Min.y + style.FramePadding.y), label);
+        RenderText(ImVec2(bb.Max.x + style.ItemInnerSpacing.x, bb.Min.y + style.FramePadding.y), label);
-
-    if ((pressed || g.NavActivateId == id) && !popup_open)
-    {
-        OpenPopupEx(popup_id, ImGuiPopupFlags_None);
-        popup_open = true;
-    }
 
     if (!popup_open)
         return false;
 
-    if (has_window_size_constraint)
+    g.NextWindowData.Flags = backup_next_window_data_flags;
+    return BeginComboPopup(popup_id, bb, flags);
+}
+
+bool ImGui::BeginComboPopup(ImGuiID popup_id, const ImRect& bb, ImGuiComboFlags flags)
+{
+    ImGuiContext& g = *GImGui;
+    if (!IsPopupOpen(popup_id, ImGuiPopupFlags_None))
+    {
+        g.NextWindowData.ClearFlags();
+        return false;
+    }
+
+    // Set popup size
+    float w = bb.GetWidth();
+    if (g.NextWindowData.Flags & ImGuiNextWindowDataFlags_HasSizeConstraint)
     {
-        g.NextWindowData.Flags |= ImGuiNextWindowDataFlags_HasSizeConstraint;
         g.NextWindowData.SizeConstraintRect.Min.x = ImMax(g.NextWindowData.SizeConstraintRect.Min.x, w);
     }
     else
     {
         if ((flags & ImGuiComboFlags_HeightMask_) == 0)
             flags |= ImGuiComboFlags_HeightRegular;
-        IM_ASSERT(ImIsPowerOfTwo(flags & ImGuiComboFlags_HeightMask_));    // Only one
+        IM_ASSERT(ImIsPowerOfTwo(flags & ImGuiComboFlags_HeightMask_)); // Only one
         int popup_max_height_in_items = -1;
         if (flags & ImGuiComboFlags_HeightRegular)     popup_max_height_in_items = 8;
         else if (flags & ImGuiComboFlags_HeightSmall)  popup_max_height_in_items = 4;
@@ -1631,11 +1646,13 @@ bool ImGui::BeginCombo(const char* label, const char* preview_value, ImGuiComboF
         SetNextWindowSizeConstraints(ImVec2(w, 0.0f), ImVec2(FLT_MAX, CalcMaxPopupHeightFromItemCount(popup_max_height_in_items)));
     }
 
+    // This is essentially a specialized version of BeginPopupEx()
     char name[16];
     ImFormatString(name, IM_ARRAYSIZE(name), "##Combo_%02d", g.BeginPopupStack.Size); // Recycle windows based on depth
 
-    // Position the window given a custom constraint (peak into expected window size so we can position it)
+    // Set position given a custom constraint (peak into expected window size so we can position it)
-    // This might be easier to express with an hypothetical SetNextWindowPosConstraints() function.
+    // FIXME: This might be easier to express with an hypothetical SetNextWindowPosConstraints() function?
+    // FIXME: This might be moved to Begin() or at least around the same spot where Tooltips and other Popups are calling FindBestWindowPosForPopupEx()?
     if (ImGuiWindow* popup_window = FindWindowByName(name))
         if (popup_window->WasActive)
         {
@@ -1643,15 +1660,13 @@ bool ImGui::BeginCombo(const char* label, const char* preview_value, ImGuiComboF
             ImVec2 size_expected = CalcWindowNextAutoFitSize(popup_window);
             popup_window->AutoPosLastDirection = (flags & ImGuiComboFlags_PopupAlignLeft) ? ImGuiDir_Left : ImGuiDir_Down; // Left = "Below, Toward Left", Down = "Below, Toward Right (default)"
             ImRect r_outer = GetPopupAllowedExtentRect(popup_window);
-            ImVec2 pos = FindBestWindowPosForPopupEx(frame_bb.GetBL(), size_expected, &popup_window->AutoPosLastDirection, r_outer, frame_bb, ImGuiPopupPositionPolicy_ComboBox);
+            ImVec2 pos = FindBestWindowPosForPopupEx(bb.GetBL(), size_expected, &popup_window->AutoPosLastDirection, r_outer, bb, ImGuiPopupPositionPolicy_ComboBox);
             SetNextWindowPos(pos);
         }
 
     // We don't use BeginPopupEx() solely because we have a custom name string, which we could make an argument to BeginPopupEx()
     ImGuiWindowFlags window_flags = ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_Popup | ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_NoMove;
-
+    PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(g.Style.FramePadding.x, g.Style.WindowPadding.y)); // Horizontally align ourselves with the framed text
-    // Horizontally align ourselves with the framed text
-    PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(style.FramePadding.x, style.WindowPadding.y));
     bool ret = Begin(name, NULL, window_flags);
     PopStyleVar();
     if (!ret)