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Fix apng write row buffer reset #886

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Fix apng write row buffer reset #886

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87a7e7a
Prevent stale APNG write row buffers across frames
p0her Jun 27, 2026
bd0601a
Keep APNG frame-size changes covered by tests
p0her Jun 27, 2026
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7 changes: 7 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -536,6 +536,8 @@ if(PNG_TESTS AND PNG_SHARED)
list(SORT PNGSUITE_PNGS)
file(GLOB TEST_PNGS "${CMAKE_CURRENT_SOURCE_DIR}/contrib/testpngs/*.png")
list(SORT TEST_PNGS)
file(GLOB TEST_APNG_PNGS "${CMAKE_CURRENT_SOURCE_DIR}/contrib/testpngs/apng/*.png")
list(SORT TEST_APNG_PNGS)
file(GLOB TEST_PNG3_PNGS "${CMAKE_CURRENT_SOURCE_DIR}/contrib/testpngs/png-3/*.png")
list(SORT TEST_PNG3_PNGS)

Expand All @@ -555,6 +557,11 @@ if(PNG_TESTS AND PNG_SHARED)
COMMAND pngtest
FILES "${TEST_PNG3_PNGS}")

png_add_test(NAME pngtest-apng
COMMAND pngtest
OPTIONS --relaxed
FILES "${TEST_APNG_PNGS}")

# pnggetset test:
# Getter-to-setter roundtrips for various chunk types.
add_executable(pnggetset ${pnggetset_sources})
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Binary file added contrib/testpngs/apng/frame-size-change.png
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15 changes: 15 additions & 0 deletions pngwutil.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2886,6 +2886,21 @@ png_write_reset(png_struct *png_ptr)
png_ptr->row_number = 0;
png_ptr->pass = 0;
png_ptr->mode &= ~PNG_HAVE_IDAT;

/* APNG frames may have different dimensions, so the row and filter
* buffers are frame-local and must be recreated for each new frame.
*/
png_free(png_ptr, png_ptr->row_buf);
png_ptr->row_buf = NULL;

#ifdef PNG_WRITE_FILTER_SUPPORTED
png_free(png_ptr, png_ptr->prev_row);
png_free(png_ptr, png_ptr->try_row);
png_free(png_ptr, png_ptr->tst_row);
png_ptr->prev_row = NULL;
png_ptr->try_row = NULL;
png_ptr->tst_row = NULL;
#endif
}

void /* PRIVATE */
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3 changes: 3 additions & 0 deletions tests/pngtest-all
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Expand Up @@ -40,6 +40,9 @@ TEST --strict "${srcdir}"/pngtest.png
# PNG-3 tests
TEST --strict "${srcdir}"/contrib/testpngs/png-3/*.png

# APNG tests
TEST --relaxed "${srcdir}"/contrib/testpngs/apng/*.png

# Various crashers
# Use --relaxed because some come from fuzzers that don't maintain CRCs
TEST --relaxed "${srcdir}"/contrib/testpngs/crashers/badcrc.png
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