Metrics: Fixed a crash when inspecting the individual draw command of…

… a foreground drawlist.

docs/CHANGELOG.txt

@@ -89,6 +89,7 @@ Other Changes:
 - Demo: Fixed requirement in 1.83 to link with imgui_demo.cpp if IMGUI_DISABLE_METRICS_WINDOW is not set. (#4171)
   Normally the right way to disable compiling the demo is to set IMGUI_DISABLE_DEMO_WINDOWS, but we want to avoid
   implying that the file is required.
+- Metrics: Fixed a crash when inspecting the individual draw command of a foreground drawlist. [@rokups]
 - Backends: Reorganized most backends (Win32, SDL, GLFW, OpenGL2/3, DX9/10/11/12, Vulkan, Allegro) to pull their
   data from a single structure stored inside the main Dear ImGui context. This facilitate/allow usage of standard
   backends with multiple-contexts BUT is only partially tested and not well supported. It is generally advised to

imgui.cpp

@@ -11480,16 +11480,17 @@ void ImGui::DebugNodeDrawList(ImGuiWindow* window, const ImDrawList* draw_list,
 void ImGui::DebugNodeDrawCmdShowMeshAndBoundingBox(ImDrawList* out_draw_list, const ImDrawList* draw_list, const ImDrawCmd* draw_cmd, bool show_mesh, bool show_aabb)
 {
     IM_ASSERT(show_mesh || show_aabb);
-    ImDrawIdx* idx_buffer = (draw_list->IdxBuffer.Size > 0) ? draw_list->IdxBuffer.Data : NULL;
-    ImDrawVert* vtx_buffer = draw_list->VtxBuffer.Data + draw_cmd->VtxOffset;
 
     // Draw wire-frame version of all triangles
     ImRect clip_rect = draw_cmd->ClipRect;
     ImRect vtxs_rect(FLT_MAX, FLT_MAX, -FLT_MAX, -FLT_MAX);
     ImDrawListFlags backup_flags = out_draw_list->Flags;
     out_draw_list->Flags &= ~ImDrawListFlags_AntiAliasedLines; // Disable AA on triangle outlines is more readable for very large and thin triangles.
-    for (unsigned int idx_n = draw_cmd->IdxOffset; idx_n < draw_cmd->IdxOffset + draw_cmd->ElemCount; )
+    for (unsigned int idx_n = draw_cmd->IdxOffset, idx_end = draw_cmd->IdxOffset + draw_cmd->ElemCount; idx_n < idx_end; )
     {
+        ImDrawIdx* idx_buffer = (draw_list->IdxBuffer.Size > 0) ? draw_list->IdxBuffer.Data : NULL; // We don't hold on those pointers past iterations as ->AddPolyline() may invalidate them if out_draw_list==draw_list
+        ImDrawVert* vtx_buffer = draw_list->VtxBuffer.Data + draw_cmd->VtxOffset;
+
         ImVec2 triangle[3];
         for (int n = 0; n < 3; n++, idx_n++)
             vtxs_rect.Add((triangle[n] = vtx_buffer[idx_buffer ? idx_buffer[idx_n] : idx_n].pos));