Canvas: Ensure canvas draw commands are separated from other ImGui draw commands (#205, #250)

Author: thedmd

docs/CHANGELOG.txt

@@ -41,6 +41,8 @@ v0.9.2 (WIP):
 
     BUGFIX: Editor: Clean long to int implicit cast warning in crude_json
 
+    BUGFIX: Canvas: Ensure canvas draw commands are separated from other ImGui draw commands (#205, #250)
+
 
 v0.9.1 (2022-08-27):
 

imgui_canvas.cpp

@@ -68,6 +68,12 @@ struct VtxCurrentOffsetRef
     }
 };
 
+static void SentinelDrawCallback(const ImDrawList* parent_list, const ImDrawCmd* cmd)
+{
+    // This is a sentinel draw callback, it's only purpose is to mark draw list command.
+    IM_ASSERT(false && "This draw callback should never be called.");
+}
+
 } // namespace ImCanvasDetails
 
 // Returns a reference to _FringeScale extension to ImDrawList
@@ -429,7 +435,7 @@ void ImGuiEx::Canvas::EnterLocalSpace()
     //
     //     More investigation is needed. To get to the bottom of this.
     if ((!m_DrawList->CmdBuffer.empty() && m_DrawList->CmdBuffer.back().ElemCount > 0) || m_DrawList->_Splitter._Count > 1)
-        m_DrawList->AddDrawCmd();
+        m_DrawList->AddCallback(&ImCanvasDetails::SentinelDrawCallback, nullptr);
 
 # if IMGUI_EX_CANVAS_DEFERED()
     m_Ranges.resize(m_Ranges.Size + 1);
@@ -547,6 +553,10 @@ void ImGuiEx::Canvas::LeaveLocalSpace()
         }
     }
 
+    // Remove sentinel draw command if present
+    if (m_DrawListCommadBufferSize > 0 && m_DrawList->CmdBuffer.size() >= m_DrawListCommadBufferSize && m_DrawList->CmdBuffer[m_DrawListCommadBufferSize - 1].UserCallback == &ImCanvasDetails::SentinelDrawCallback)
+        m_DrawList->CmdBuffer.erase(m_DrawList->CmdBuffer.Data + m_DrawListCommadBufferSize - 1);
+
     auto& fringeScale = ImFringeScaleRef(m_DrawList);
     fringeScale = m_LastFringeScale;