From d7e35727f17e998703cfbb00ac8647705fb56c7d Mon Sep 17 00:00:00 2001
From: Kyle Isom <kyle@imap.cc>
Date: Wed, 25 Mar 2026 02:07:31 -0700
Subject: [PATCH] Fix segfault from mid-frame font atlas rebuild

The edit-mode font switcher called LoadFont() directly between
NewFrame() and Render(), invalidating the font atlas ImGui was
actively using. Use RequestLoadFont() to defer the change to
the safe inter-frame point, matching the existing zoom pattern.

Also default code_font/writing_font to the main font when not
explicitly configured, preventing a mismatch that triggered the
switch on every first frame.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 GUIConfig.cc     | 29 +++++++++++++++++++++++++++--
 ImGuiFrontend.cc |  4 +---
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/GUIConfig.cc b/GUIConfig.cc
index ac62dc7..daf1f54 100644
--- a/GUIConfig.cc
+++ b/GUIConfig.cc
@@ -99,16 +99,22 @@ GUIConfig::LoadFromTOML(const std::string &path)
 	}
 
 	// [font]
+	bool explicit_code_font    = false;
+	bool explicit_writing_font = false;
 	if (auto sec = tbl["font"].as_table()) {
 		if (auto v = (*sec)["name"].value<std::string>())
 			font = *v;
 		if (auto v = (*sec)["size"].value<double>()) {
 			if (*v > 0.0) font_size = static_cast<float>(*v);
 		}
-		if (auto v = (*sec)["code"].value<std::string>())
+		if (auto v = (*sec)["code"].value<std::string>()) {
 			code_font = *v;
-		if (auto v = (*sec)["writing"].value<std::string>())
+			explicit_code_font = true;
+		}
+		if (auto v = (*sec)["writing"].value<std::string>()) {
 			writing_font = *v;
+			explicit_writing_font = true;
+		}
 	}
 
 	// [appearance]
@@ -131,6 +137,12 @@ GUIConfig::LoadFromTOML(const std::string &path)
 			syntax = *v;
 	}
 
+	// Default code_font to the main font if not explicitly set
+	if (!explicit_code_font)
+		code_font = font;
+	if (!explicit_writing_font && writing_font == "crimsonpro" && font != "default")
+		writing_font = font;
+
 	return true;
 }
 
@@ -142,6 +154,9 @@ GUIConfig::LoadFromINI(const std::string &path)
 	if (!in.good())
 		return false;
 
+	bool explicit_code_font    = false;
+	bool explicit_writing_font = false;
+
 	std::string line;
 	while (std::getline(in, line)) {
 		// Remove comments starting with '#' or ';'
@@ -198,8 +213,10 @@ GUIConfig::LoadFromINI(const std::string &path)
 			font = val;
 		} else if (key == "code_font") {
 			code_font = val;
+			explicit_code_font = true;
 		} else if (key == "writing_font") {
 			writing_font = val;
+			explicit_writing_font = true;
 		} else if (key == "theme") {
 			theme = val;
 		} else if (key == "background" || key == "bg") {
@@ -222,5 +239,13 @@ GUIConfig::LoadFromINI(const std::string &path)
 		}
 	}
 
+	// If code_font was not explicitly set, default it to the main font
+	// so that the edit-mode font switcher doesn't immediately switch away
+	// from the font loaded during Init.
+	if (!explicit_code_font)
+		code_font = font;
+	if (!explicit_writing_font && writing_font == "crimsonpro" && font != "default")
+		writing_font = font;
+
 	return true;
 }
diff --git a/ImGuiFrontend.cc b/ImGuiFrontend.cc
index d21175f..57a961f 100644
--- a/ImGuiFrontend.cc
+++ b/ImGuiFrontend.cc
@@ -577,9 +577,7 @@ GUIFrontend::Step(Editor &ed, bool &running)
 				if (fr.CurrentFontName() != expected && fr.HasFont(expected)) {
 					float sz = fr.CurrentFontSize();
 					if (sz <= 0.0f) sz = config_.font_size;
-					fr.LoadFont(expected, sz);
-					ImGui_ImplOpenGL3_DestroyFontsTexture();
-					ImGui_ImplOpenGL3_CreateFontsTexture();
+					fr.RequestLoadFont(expected, sz);
 				}
 			}
 		}