From 0647cf434c3eca69343471c5d5eb6d6e03183547 Mon Sep 17 00:00:00 2001
From: ocornut <omarcornut@gmail.com>
Date: Wed, 8 Dec 2021 17:02:24 +0100
Subject: [PATCH] Nav, Docking: Fix crash on dimming docked window and
 DockSpaceOverViewport() with PassthruCentralNode.

(amend 1dc3af3, 23ef6c1, 657073a)
---
 imgui.cpp      | 7 ++++++-
 imgui_draw.cpp | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/imgui.cpp b/imgui.cpp
index 92e97495..fa971f1f 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -4636,7 +4636,11 @@ static void ImGui::RenderDimmedBackgroundBehindWindow(ImGuiWindow* window, ImU32
 
     // Draw behind window by moving the draw command at the FRONT of the draw list
     {
+        // We've already called AddWindowToDrawData() which called DrawList->ChannelsMerge() on DockNodeHost windows,
+        // and draw list have been trimmed already, hence the explicit recreation of a draw command if missing.
         ImDrawList* draw_list = window->RootWindowDockTree->DrawList;
+        if (draw_list->CmdBuffer.Size == 0)
+            draw_list->AddDrawCmd();
         draw_list->PushClipRect(viewport_rect.Min - ImVec2(1, 1), viewport_rect.Max + ImVec2(1, 1), false); // Ensure ImDrawCmd are not merged
         draw_list->AddRectFilled(viewport_rect.Min, viewport_rect.Max, col);
         ImDrawCmd cmd = draw_list->CmdBuffer.back();
@@ -4651,7 +4655,6 @@ static void ImGui::RenderDimmedBackgroundBehindWindow(ImGuiWindow* window, ImU32
     {
         ImDrawList* draw_list = FindFrontMostVisibleChildWindow(window->RootWindowDockTree)->DrawList;
         draw_list->PushClipRect(viewport_rect.Min, viewport_rect.Max, false);
-        //if (window->RootWindowDockTree != window->RootWindow)
         RenderRectFilledWithHole(draw_list, window->RootWindowDockTree->Rect(), window->RootWindow->Rect(), col, 0.0f);// window->RootWindowDockTree->WindowRounding);
         draw_list->PopClipRect();
     }
@@ -4690,6 +4693,8 @@ static void ImGui::RenderDimmedBackgrounds()
         bb.Expand(distance);
         if (bb.GetWidth() >= viewport->Size.x && bb.GetHeight() >= viewport->Size.y)
             bb.Expand(-distance - 1.0f); // If a window fits the entire viewport, adjust its highlight inward
+        if (window->DrawList->CmdBuffer.Size == 0)
+            window->DrawList->AddDrawCmd();
         window->DrawList->PushClipRect(viewport->Pos, viewport->Pos + viewport->Size);
         window->DrawList->AddRect(bb.Min, bb.Max, GetColorU32(ImGuiCol_NavWindowingHighlight, g.NavWindowingHighlightAlpha), window->WindowRounding, 0, 3.0f);
         window->DrawList->PopClipRect();
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index 6a24a8ca..bcc320d8 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -481,6 +481,7 @@ void ImDrawList::_PopUnusedDrawCmd()
 
 void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
 {
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     IM_ASSERT(curr_cmd->UserCallback == NULL);
     if (curr_cmd->ElemCount != 0)
@@ -502,6 +503,7 @@ void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
 // Try to merge two last draw commands
 void ImDrawList::_TryMergeDrawCmds()
 {
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     ImDrawCmd* prev_cmd = curr_cmd - 1;
     if (ImDrawCmd_HeaderCompare(curr_cmd, prev_cmd) == 0 && curr_cmd->UserCallback == NULL && prev_cmd->UserCallback == NULL)
@@ -516,6 +518,7 @@ void ImDrawList::_TryMergeDrawCmds()
 void ImDrawList::_OnChangedClipRect()
 {
     // If current command is used with different settings we need to add a new command
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     if (curr_cmd->ElemCount != 0 && memcmp(&curr_cmd->ClipRect, &_CmdHeader.ClipRect, sizeof(ImVec4)) != 0)
     {
@@ -538,6 +541,7 @@ void ImDrawList::_OnChangedClipRect()
 void ImDrawList::_OnChangedTextureID()
 {
     // If current command is used with different settings we need to add a new command
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     if (curr_cmd->ElemCount != 0 && curr_cmd->TextureId != _CmdHeader.TextureId)
     {
@@ -561,6 +565,7 @@ void ImDrawList::_OnChangedVtxOffset()
 {
     // We don't need to compare curr_cmd->VtxOffset != _CmdHeader.VtxOffset because we know it'll be different at the time we call this.
     _VtxCurrentIdx = 0;
+    IM_ASSERT_PARANOID(CmdBuffer.Size > 0);
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
     //IM_ASSERT(curr_cmd->VtxOffset != _CmdHeader.VtxOffset); // See #3349
     if (curr_cmd->ElemCount != 0)