From b2343d62474e87b241c6cd2e27464142bb2dd2ba Mon Sep 17 00:00:00 2001
From: ocornut <omar@miracleworld.net>
Date: Tue, 20 May 2025 19:56:27 +0200
Subject: [PATCH] Fonts: fallback to default default rasterizer density + pick
 one from existing viewports at the time of calling AddUpdateViewport().

# Conflicts:
#	imgui.cpp
---
 imgui.cpp      | 6 +++++-
 imgui_draw.cpp | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/imgui.cpp b/imgui.cpp
index 13cb78f0b..d869da7fe 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -4399,7 +4399,10 @@ static void SetCurrentWindow(ImGuiWindow* window)
     if (window)
     {
         if (g.IO.BackendFlags & ImGuiBackendFlags_RendererHasTextures)
-            g.FontRasterizerDensity = window->Viewport->FramebufferScale.x; // == SetFontRasterizerDensity()
+        {
+            ImGuiViewport* viewport = window->Viewport;
+            g.FontRasterizerDensity = (viewport->FramebufferScale.x != 0.0f) ? viewport->FramebufferScale.x : g.IO.DisplayFramebufferScale.x; // == SetFontRasterizerDensity()
+        }
         ImGui::UpdateCurrentFontSize();
         ImGui::NavUpdateCurrentWindowIsScrollPushableX();
     }
@@ -15249,6 +15252,7 @@ static void ImGui::UpdateViewportsNewFrame()
     main_viewport->Pos = ImVec2(0.0f, 0.0f);
     main_viewport->Size = g.IO.DisplaySize;
     main_viewport->FramebufferScale = g.IO.DisplayFramebufferScale;
+    IM_ASSERT(main_viewport->FramebufferScale.x > 0.0f && main_viewport->FramebufferScale.y > 0.0f);
 
     for (ImGuiViewportP* viewport : g.Viewports)
     {
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index 3d719820f..93f5fdf8d 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -5225,6 +5225,7 @@ ImFontBaked* ImFontAtlasBakedGetOrAdd(ImFontAtlas* atlas, ImFont* font, float fo
 {
     // FIXME-NEWATLAS: Design for picking a nearest size based on some criteria?
     // FIXME-NEWATLAS: Altering font density won't work right away.
+    IM_ASSERT(font_size > 0.0f && font_rasterizer_density > 0.0f);
     ImGuiID baked_id = ImFontAtlasBakedGetId(font->FontId, font_size, font_rasterizer_density);
     ImFontAtlasBuilder* builder = atlas->Builder;
     ImFontBaked** p_baked_in_map = (ImFontBaked**)builder->BakedMap.GetVoidPtrRef(baked_id);