From 58e11305710a506ce3369581662eeb14440639cf Mon Sep 17 00:00:00 2001
From: Lei Zhang <thestig@chromium.org>
Date: Tue, 06 Oct 2026 16:12:29 -0700
Subject: [PATCH] Correctly initialize current cell in agg::outline_aa

Initialize `m_cur_cell` to (0x7FFFFFFF, 0x7FFFFFFF) instead of
(0x7FFF, 0x7FFF) in outline_aa::outline_aa() and outline_aa::reset(),
matching `m_min_x` and `m_min_y`.

Previously, if a path started at cell (0x7FFF, 0x7FFF),
outline_aa::set_cur_cell() treated the coordinates as unchanged and
skipped updating `m_min_x`, `m_max_x`, `m_min_y`, and `m_max_y`. This
left the bounds out of sync with the cells in `m_cells`, leading to
out-of-bounds memory accesses in outline_aa::sort_cells() and
rasterizer_scanline_aa::sweep_scanline(). Since cell coordinates passed
to outline_aa::set_cur_cell() are shifted right by `poly_base_shift`,
they can never equal 0x7FFFFFFF.

This matches the equivalent code in newer versions of AGG.

TAG=agy
CONV=c8cb5ce3-fe6b-4ebe-8831-b653899043f0

Bug: 570167922
Change-Id: I5e06c418226e67ff7487e4e8bba6233402a4ea8e
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/160091
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
---
diff --git a/third_party/agg23/0018-outline_aa_reset.patch b/third_party/agg23/0018-outline_aa_reset.patch
new file mode 100644
index 0000000..7d9c8d6
--- /dev/null
+++ b/third_party/agg23/0018-outline_aa_reset.patch
@@ -0,0 +1,20 @@
+diff --git a/third_party/agg23/agg_rasterizer_scanline_aa.cpp b/third_party/agg23/agg_rasterizer_scanline_aa.cpp
+index ed59cf0ffb..d561e02b58 100644
+--- a/third_party/agg23/agg_rasterizer_scanline_aa.cpp
++++ b/third_party/agg23/agg_rasterizer_scanline_aa.cpp
+@@ -101,13 +101,13 @@ outline_aa::outline_aa() :
+     m_max_y(-0x7FFFFFFF),
+     m_sorted(false)
+ {
+-    m_cur_cell.set(0x7FFF, 0x7FFF, 0, 0);
++    m_cur_cell.set(0x7FFFFFFF, 0x7FFFFFFF, 0, 0);
+ }
+ void outline_aa::reset()
+ {
+     m_num_cells = 0;
+     m_cur_block = 0;
+-    m_cur_cell.set(0x7FFF, 0x7FFF, 0, 0);
++    m_cur_cell.set(0x7FFFFFFF, 0x7FFFFFFF, 0, 0);
+     m_sorted = false;
+     m_min_x =  0x7FFFFFFF;
+     m_min_y =  0x7FFFFFFF;
diff --git a/third_party/agg23/README.pdfium b/third_party/agg23/README.pdfium
index a40bb08..f0bc592 100644
--- a/third_party/agg23/README.pdfium
+++ b/third_party/agg23/README.pdfium
@@ -39,3 +39,4 @@
 0016-support-negative-dash-phases.patch: Support negative dash phases in
 calc_dash_start().
 0017-support-odd-size-dash-arrays.patch: Support odd-sized dash arrays.
+0018-outline_aa_reset.patch: Correctly reset current cell.
diff --git a/third_party/agg23/agg_rasterizer_scanline_aa.cpp b/third_party/agg23/agg_rasterizer_scanline_aa.cpp
index ed59cf0..d561e02 100644
--- a/third_party/agg23/agg_rasterizer_scanline_aa.cpp
+++ b/third_party/agg23/agg_rasterizer_scanline_aa.cpp
@@ -101,13 +101,13 @@
     m_max_y(-0x7FFFFFFF),
     m_sorted(false)
 {
-    m_cur_cell.set(0x7FFF, 0x7FFF, 0, 0);
+    m_cur_cell.set(0x7FFFFFFF, 0x7FFFFFFF, 0, 0);
 }
 void outline_aa::reset()
 {
     m_num_cells = 0;
     m_cur_block = 0;
-    m_cur_cell.set(0x7FFF, 0x7FFF, 0, 0);
+    m_cur_cell.set(0x7FFFFFFF, 0x7FFFFFFF, 0, 0);
     m_sorted = false;
     m_min_x =  0x7FFFFFFF;
     m_min_y =  0x7FFFFFFF;