Internals: Checkbox: Added undocumented mixed/indeterminate/tristate support via ImGuiItemFlags_MixedValue. (#2644)

docs/TODO.txt

@@ -65,7 +65,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - widgets: start exposing PushItemFlag() and ImGuiItemFlags
  - widgets: alignment options in style (e.g. center Selectable, Right-Align within Button, etc.) #1260
  - widgets: activate by identifier (trigger button, focus given id)
- - widgets: a way to represent "mixed" values, so e.g. all values replaced with **, including check-boxes, colors, etc. with support for multi-components widgets (e.g. SliderFloat3, make only "Y" mixed)
+ - widgets: a way to represent "mixed" values, so e.g. all values replaced with *, including check-boxes, colors, etc. with support for multi-components widgets (e.g. SliderFloat3, make only "Y" mixed) (#2644)
  - widgets: selectable: generic BeginSelectable()/EndSelectable() mechanism.
  - widgets: selectable: a way to visualize partial/mixed selection (e.g. parent tree node has children with mixed selection)
  - widgets: checkbox: checkbox with custom glyph inside frame.

imgui_internal.h

@@ -384,6 +384,7 @@ enum ImGuiItemFlags_
     ImGuiItemFlags_NoNav                    = 1 << 3,  // false
     ImGuiItemFlags_NoNavDefaultFocus        = 1 << 4,  // false
     ImGuiItemFlags_SelectableDontClosePopup = 1 << 5,  // false    // MenuItem/Selectable() automatically closes current Popup window
+    ImGuiItemFlags_MixedValue               = 1 << 6,  // false    // [BETA] Represent a mixed/indeterminate value, generally multi-selection where values differ. Currently only supported by Checkbox() (later should support all sorts of widgets)
     ImGuiItemFlags_Default_                 = 0
 };
 

imgui_widgets.cpp

@@ -1001,10 +1001,17 @@ bool ImGui::Checkbox(const char* label, bool* v)
     const ImRect check_bb(pos, pos + ImVec2(square_sz, square_sz));
     RenderNavHighlight(total_bb, id);
     RenderFrame(check_bb.Min, check_bb.Max, GetColorU32((held && hovered) ? ImGuiCol_FrameBgActive : hovered ? ImGuiCol_FrameBgHovered : ImGuiCol_FrameBg), true, style.FrameRounding);
-    if (*v)
+    ImU32 check_col = GetColorU32(ImGuiCol_CheckMark);
+    if (window->DC.ItemFlags & ImGuiItemFlags_MixedValue)
+    {
+        // Undocumented tristate/mixed/indeterminate checkbox (#2644)
+        ImVec2 pad(ImMax(1.0f, (float)(int)(square_sz / 3.6f)), ImMax(1.0f, (float)(int)(square_sz / 3.6f)));
+        window->DrawList->AddRectFilled(check_bb.Min + pad, check_bb.Max - pad, check_col, style.FrameRounding);
+    }
+    else if (*v)
     {
         const float pad = ImMax(1.0f, (float)(int)(square_sz / 6.0f));
-        RenderCheckMark(check_bb.Min + ImVec2(pad, pad), GetColorU32(ImGuiCol_CheckMark), square_sz - pad*2.0f);
+        RenderCheckMark(check_bb.Min + ImVec2(pad, pad), check_col, square_sz - pad*2.0f);
     }
 
     if (g.LogEnabled)