From 779a49acde85153ac027320d1e4b9dfd0a33a908 Mon Sep 17 00:00:00 2001
From: Strykar <2946372+Strykar@users.noreply.github.com>
Date: Wed, 10 Jun 2026 13:57:30 +0530
Subject: [PATCH] fonts: preserve the font matrix when specializing a
 descriptor

specialize_font_descriptor() re-resolves a descriptor by file, index,
size and dpi to pick up size dependent fields. The re-match carries no
slant request, so fontconfig cannot re-derive a synthetic italic matrix,
and only index, named_style and axes were copied back from the base
descriptor. Any FC_MATRIX on the descriptor was therefore lost on every
sized face build, so the face was constructed without it and
FT_Set_Transform was never called, rendering the glyphs upright.

Descriptors can carry FC_MATRIX since b3e7c3e ("Read FC_MATRIX from
fontconfig"). Copy the matrix back like the other selection derived
fields the re-match cannot reproduce.
---
 kitty/fontconfig.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kitty/fontconfig.c b/kitty/fontconfig.c
index 388ccf8b1..a7847468e 100644
--- a/kitty/fontconfig.c
+++ b/kitty/fontconfig.c
@@ -458,6 +458,10 @@ specialize_font_descriptor(PyObject *base_descriptor, double font_sz_in_pts, dou
     if (axes) {
         if (PyDict_SetItemString(ans, "axes", axes) != 0) return NULL;
     }
+    PyObject *matrix = PyDict_GetItemString(base_descriptor, "matrix");
+    if (matrix) {
+        if (PyDict_SetItemString(ans, "matrix", matrix) != 0) return NULL;
+    }
     PyObject *ff = PyDict_GetItemString(ans, "fontfeatures");
     if (ff && PyList_GET_SIZE(ff)) {
         for (Py_ssize_t i = 0; i < PyList_GET_SIZE(ff); i++) {