AVIF support (#671)

Demand for AVIF support on the web is growing, as the word gets out
about this new file format which allows higher-quality encoding at
smaller sizes.  Core contributors to major open-source CMSs are
interested in auto-generating AVIF images! They've been simply
waiting for support to appear in libgd.

This PR aims to meet the growing demand, and to help bring smaller,
more beautiful images to more of the web - to sites created by
experienced developers and CMS users alike.

This PR adds support by incorporating libavif in addition to the
existing libheif support.  It's generally felt that libavif has
more complete support for the AVIF format. libavif is also used
by the Chromium project and squoosh.app.

In this PR, I've endeavored to incorporate the latest research into
best practices for AVIF encoding - not just for default quantizer
values, but also an algorithm for determining the number of
horizontal tiles, vertical tiles, and threads.

Fixes #557.

39 files changed, 1351 insertions, 9 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b13767d..57cd95d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,6 +20,7 @@ OPTION(ENABLE_FREETYPE "Enable Freetype2 support" 0)
 OPTION(ENABLE_FONTCONFIG "Enable FontConfig support" 0)
 OPTION(ENABLE_WEBP "Enable WebP support" 0)
 OPTION(ENABLE_HEIF "Enable HEIF support" 0)
+OPTION(ENABLE_AVIF "Enable AVIF support" 0)
 OPTION(ENABLE_RAQM "Enable RAQM support" 0)
 
 if (BUILD_TEST)
@@ -124,6 +125,13 @@ else (USE_EXT_GD)
 		FIND_PACKAGE(HEIF REQUIRED)
 	ENDIF (ENABLE_HEIF)
 
+	IF (ENABLE_AVIF)
+		FIND_PACKAGE(libavif 0.8.2 REQUIRED CONFIG)
+		SET(HAVE_LIBAVIF 1)
+		SET(AVIF_LIBRARIES avif)
+		SET(AVIF_FOUND 1)
+	ENDIF (ENABLE_AVIF)
+
 	IF (ENABLE_LIQ)
 		FIND_PACKAGE(LIQ REQUIRED)
 	ENDIF (ENABLE_LIQ)
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 55f386f..cdb066a 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -1,3 +1,4 @@
+Ben Morss (morsssss)
 chapg
 Chen Pingping (Wilson)
 Chris Reuter
diff --git a/README.md b/README.md
index 96268ea..aa8fa3f 100644
--- a/README.md
+++ b/README.md
@@ -39,8 +39,9 @@ GD has builtin support for:
 
 It also has optional support for more formats via external libraries:
 
+* [AVIF](https://en.wikipedia.org/wiki/AV1#AV1_Image_File_Format_(AVIF)) via [libavif](https://github.com/AOMediaCodec/libavif)
 * [HEIF](https://en.wikipedia.org/wiki/High_Efficiency_Image_File_Format) via [libheif](https://github.com/strukturag/libheif/)
-  * Also it includes [AVIF](https://en.wikipedia.org/wiki/AV1#AV1_Image_File_Format_%28AVIF%29) read support if your system's `libheif` has AV1 decoding.
+  * This includes [AVIF](https://en.wikipedia.org/wiki/AV1#AV1_Image_File_Format_%28AVIF%29) read support if your system's `libheif` has AV1 decoding.
 * [JPEG](https://en.wikipedia.org/wiki/JPEG) via [IJG/libjpeg](http://www.ijg.org/) or [libjpeg-turbo](http://libjpeg-turbo.virtualgl.org/)
   * Does not include [JPEG 2000](https://en.wikipedia.org/wiki/JPEG_2000)
 * [PNG](https://en.wikipedia.org/wiki/Portable_Network_Graphics) via [libpng](http://www.libpng.org/)
diff --git a/configure.ac b/configure.ac
index 5a4c357..535db68 100644
--- a/configure.ac
+++ b/configure.ac
@@ -289,6 +289,13 @@ dnl Check for heif support.
 GD_LIB_PKG_CHECK([LIBHEIF], [HEIF], [heif], [libheif >= 1.7.0], [
   AC_CHECK_LIB([heif], [heif_get_version], [dnl
     AS_VAR_APPEND([LIBHEIF_LIBS], [" -lheif"])
+  ])
+])
+
+dnl Check for avif support.
+GD_LIB_PKG_CHECK([LIBAVIF], [AVIF], [avif], [libavif >= 0.8.2], [
+  AC_CHECK_LIB([avif], [avifVersion], [dnl
+    AS_VAR_APPEND([LIBAVIF_LIBS], [" -lavif"])
     gd_found_lib=yes
   ])
 ])
@@ -323,6 +330,7 @@ AC_MSG_RESULT([
    Support for JPEG library:         $gd_with_LIBJPEG
    Support for WebP library:         $gd_with_LIBWEBP
    Support for HEIF library:         $gd_with_LIBHEIF
+   Support for AVIF library:         $gd_with_LIBAVIF
    Support for TIFF library:         $gd_with_LIBTIFF
    Support for Freetype 2.x library: $gd_with_LIBFREETYPE
    Support for Fontconfig library:   $gd_with_LIBFONTCONFIG
diff --git a/docs/README.CMAKE b/docs/README.CMAKE
index 2be2045..c9356b2 100644
--- a/docs/README.CMAKE
+++ b/docs/README.CMAKE
@@ -20,6 +20,7 @@ ENABLE_FREETYPE=1
 ENABLE_FONTCONFIG=1
 ENABLE_XPM=1
 ENABLE_WEBP=1
+ENABLE_AVIF=1
 ENABLE_RAQM=1
 
 You can optionally run our tests suite using:
diff --git a/docs/naturaldocs/project/Menu.txt b/docs/naturaldocs/project/Menu.txt
index 250d988..12df023 100644
--- a/docs/naturaldocs/project/Menu.txt
+++ b/docs/naturaldocs/project/Menu.txt
@@ -50,6 +50,7 @@ File: About LibGD 2.3.0-dev  (no auto-title, preamble.txt)
 
 Group: Image Formats  {
 
+   File: AVIF IO  (no auto-title, gd_avif.c)
    File: BMP IO  (no auto-title, gd_bmp.c)
    File: GD IO  (no auto-title, gd_gd.c)
    File: GD2 IO  (no auto-title, gd_gd2.c)
diff --git a/examples/avif2jpeg.c b/examples/avif2jpeg.c
new file mode 100644
index 0000000..6ced15d
--- /dev/null
+++ b/examples/avif2jpeg.c
@@ -0,0 +1,55 @@
+/**
+ * A short program which converts a .avif file into a .jpg file -
+ * just to get a little practice with the basic functionality.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif /* HAVE_CONFIG_H */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "gd.h"
+
+int main(int argc, char **argv)
+{
+	gdImagePtr im;
+	FILE *in, *out;
+
+	if (argc != 3) {
+		fprintf(stderr, "Usage: avif2jpeg infile.avif outfile.jpg\n");
+		exit(1);
+	}
+
+	printf("Reading infile %s\n", argv[1]);
+
+	in = fopen(argv[1], "rb");
+	if (!in) {
+		fprintf(stderr, "\nError: input file %s does not exist.\n", argv[1]);
+		exit(1);
+	}
+
+	im = gdImageCreateFromAvif(in);
+	fclose(in);
+	if (!im) {
+		fprintf(stderr, "\nError: input file %s is not in AVIF format.\n", argv[1]);
+		exit(1);
+	}
+
+	out = fopen(argv[2], "wb");
+	if (!out) {
+		fprintf(stderr, "\nError: can't write to output file %s\n", argv[2]);
+		gdImageDestroy(im);
+		exit(1);
+	}
+
+	gdImageJpeg(im, out, 75);
+
+	printf("Wrote outfile %s.\n", argv[2]);
+
+	fclose(out);
+	gdImageDestroy(im);
+
+	return 0;
+}
diff --git a/examples/jpeg2avif.c b/examples/jpeg2avif.c
new file mode 100644
index 0000000..af55201
--- /dev/null
+++ b/examples/jpeg2avif.c
@@ -0,0 +1,57 @@
+/**
+ * A short program which converts a .jpg file into a .avif file -
+ * just to get a little practice with the basic functionality.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif /* HAVE_CONFIG_H */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "gd.h"
+
+int main(int argc, char **argv)
+{
+	gdImagePtr im;
+	FILE *in, *out;
+
+	if (argc != 3) {
+		fprintf(stderr, "Usage: jpeg2avif filename.jpg filename.avif\n");
+		exit(1);
+	}
+
+	printf("Reading infile %s\n", argv[1]);
+
+	in = fopen(argv[1], "rb");
+	if (!in) {
+		fprintf(stderr, "Error: input file %s does not exist.\n", argv[1]);
+		exit(1);
+	}
+
+	im = gdImageCreateFromJpeg(in);
+	fclose(in);
+	if (!im) {
+		fprintf(stderr, "Error: input file %s is not in JPEG format.\n", argv[1]);
+		exit(1);
+	}
+
+	out = fopen(argv[2], "wb");
+	if (!out) {
+		fprintf(stderr, "Error: can't write to output file %s\n", argv[2]);
+		gdImageDestroy(im);
+		exit(1);
+	}
+
+	fprintf(stderr, "Encoding...\n");
+
+	gdImageAvif(im, out);
+
+	printf("Wrote outfile %s.\n", argv[2]);
+
+	fclose(out);
+	gdImageDestroy(im);
+
+	return 0;
+}
diff --git a/examples/jpeg2avifex.c b/examples/jpeg2avifex.c
new file mode 100644
index 0000000..a8afb3b
--- /dev/null
+++ b/examples/jpeg2avifex.c
@@ -0,0 +1,98 @@
+/**
+ * A short program which converts a .jpg file into a .avif file -
+ * just to get a little practice with the basic functionality.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif /* HAVE_CONFIG_H */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+#include "gd.h"
+
+static void usage() {
+	fprintf(stderr, "Usage: jpeg2avifex [-q quality] [-s speed] infile.jpg outfile.avif\n");
+	exit(1);
+}
+
+int main(int argc, char **argv)
+{
+	gdImagePtr im;
+	FILE *in, *out;
+	int c;
+	int speed = -1, quality = -1; // use default values if unspecified
+	char *infile, *outfile;
+	int failed = 0;
+
+	if (argc < 3) {
+		usage();
+	}
+
+	while ((c = getopt(argc, argv, "q:s:")) != -1) {
+		switch (c) {
+			case 'q':
+				quality = atoi(optarg);
+				break;
+
+			case 's':
+				speed = atoi(optarg);
+				break;
+
+			default:
+				usage();
+		}
+	}
+
+	if (optind > argc - 2)
+		usage();
+
+	infile = strdup(argv[optind++]);
+	outfile = strdup(argv[optind]);
+
+	printf("Reading infile %s\n", infile);
+
+	in = fopen(infile, "rb");
+	if (!in) {
+		fprintf(stderr, "\nError: input file %s does not exist.\n", infile);
+		failed = 1;
+		goto cleanup;
+	}
+
+	im = gdImageCreateFromJpeg(in);
+	fclose(in);
+	if (!im) {
+		fprintf(stderr, "\nError: input file %s is not in JPEG format.\n", infile);
+		failed = 1;
+		goto cleanup;
+	}
+
+	out = fopen(outfile, "wb");
+	if (!out) {
+		fprintf(stderr, "\nError: can't write to output file %s\n", outfile);
+		failed = 1;
+		goto cleanup;
+	}
+
+	fprintf(stderr, "Encoding...\n");
+
+	gdImageAvifEx(im, out, quality, speed);
+
+	printf("Wrote outfile %s.\n", outfile);
+
+	fclose(out);
+
+cleanup:
+	if (im)
+		gdImageDestroy(im);
+
+	gdFree(infile);
+	gdFree(outfile);
+
+	exit(failed);
+}
diff --git a/examples/png2avif.c b/examples/png2avif.c
new file mode 100644
index 0000000..18463e7
--- /dev/null
+++ b/examples/png2avif.c
@@ -0,0 +1,58 @@
+/**
+ * A short program which converts a .png file into a .avif file -
+ * just to get a little practice with the basic functionality.
+ * We convert losslessly.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif /* HAVE_CONFIG_H */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "gd.h"
+
+int main(int argc, char **argv)
+{
+	gdImagePtr im;
+	FILE *in, *out;
+
+	if (argc != 3) {
+		fprintf(stderr, "Usage: png2avif infile.png outfile.avif\n");
+		exit(1);
+	}
+
+	printf("Reading infile %s\n", argv[1]);
+
+	in = fopen(argv[1], "rb");
+	if (!in) {
+		fprintf(stderr, "Error: input file %s does not exist.\n", argv[1]);
+		exit(1);
+	}
+
+	im = gdImageCreateFromPng(in);
+	fclose(in);
+	if (!im) {
+		fprintf(stderr, "Error: input file %s is not in PNG format.\n", argv[1]);
+		exit(1);
+	}
+
+	out = fopen(argv[2], "wb");
+	if (!out) {
+		fprintf(stderr, "Error: can't write to output file %s\n", argv[2]);
+		gdImageDestroy(im);
+		exit(1);
+	}
+
+	fprintf(stderr, "Encoding...\n");
+
+	gdImageAvifEx(im, out, 100, 0);
+
+	printf("Wrote outfile %s.\n", argv[2]);
+
+	fclose(out);
+	gdImageDestroy(im);
+
+	return 0;
+}
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ccd76e9..509c422 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -2,6 +2,7 @@ SET (LIBGD_SRC_FILES
 	bmp.h
 	gd.c
 	gd.h
+	gd_avif.c
 	gd_bmp.c
 	gd_color.c
 	gd_color.h
@@ -130,6 +131,7 @@ SET(LIBGD_DEP_LIBS
 	${XPM_LIBRARIES}
 	${FONTCONFIG_LIBRARY}
 	${WEBP_LIBRARIES}
+	${AVIF_LIBRARIES}
 	${RAQM_LIBRARIES}
 	${HEIF_LIBRARIES}
 )
diff --git a/src/Makefile.am b/src/Makefile.am
index 69a5c18..09bf192 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -60,6 +60,7 @@ libgd_la_SOURCES = \
 	bmp.h \
 	gd.c \
 	gd.h \
+	gd_avif.c \
 	gd_bmp.c \
 	gd_color.c \
 	gd_color.h \
diff --git a/src/config.h.cmake b/src/config.h.cmake
index fb86f3c..2b46a17 100644
--- a/src/config.h.cmake
+++ b/src/config.h.cmake
@@ -27,12 +27,18 @@
 /* Define to 1 if you have the <inttypes.h> header file. */
 #cmakedefine HAVE_INTTYPES_H
 
+/* Define if you have avif */
+#cmakedefine HAVE_LIBAVIF
+
 /* Define if you have fontconfig */
 #cmakedefine HAVE_LIBFONTCONFIG
 
 /* Define if you have freetype */
 #cmakedefine HAVE_LIBFREETYPE
 
+/* Define if you have heif */
+#cmakedefine HAVE_LIBHEIF
+
 /* Define if you have liq */
 #cmakedefine HAVE_LIBIMAGEQUANT
 
@@ -54,9 +60,6 @@
 /* Define if you have webp */
 #cmakedefine HAVE_LIBWEBP
 
-/* Define if you have heif */
-#cmakedefine HAVE_LIBHEIF
-
 /* Define if you have xpm */
 #cmakedefine HAVE_LIBXPM
 
diff --git a/src/gd.h b/src/gd.h
index 55fa5b3..7b5870f 100644
--- a/src/gd.h
+++ b/src/gd.h
@@ -668,6 +668,10 @@ BGD_DECLARE(gdImagePtr) gdImageCreateFromHeif(FILE *inFile);
 BGD_DECLARE(gdImagePtr) gdImageCreateFromHeifPtr(int size, void *data);
 BGD_DECLARE(gdImagePtr) gdImageCreateFromHeifCtx(gdIOCtx *infile);
 
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvif(FILE *inFile);
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvifPtr(int size, void *data);
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvifCtx(gdIOCtx *infile);
+
 BGD_DECLARE(gdImagePtr) gdImageCreateFromTiff(FILE *inFile);
 BGD_DECLARE(gdImagePtr) gdImageCreateFromTiffCtx(gdIOCtx *infile);
 BGD_DECLARE(gdImagePtr) gdImageCreateFromTiffPtr(int size, void *data);
@@ -1131,6 +1135,11 @@ BGD_DECLARE(void *) gdImageHeifPtr(gdImagePtr im, int *size);
 BGD_DECLARE(void *) gdImageHeifPtrEx(gdImagePtr im, int *size, int quality, gdHeifCodec codec, gdHeifChroma chroma);
 BGD_DECLARE(void) gdImageHeifCtx(gdImagePtr im, gdIOCtx *outfile, int quality, gdHeifCodec codec, gdHeifChroma chroma);
 
+BGD_DECLARE(void) gdImageAvif(gdImagePtr im, FILE *outFile);
+BGD_DECLARE(void) gdImageAvifEx(gdImagePtr im, FILE *outFile, int quality, int speed);
+BGD_DECLARE(void *) gdImageAvifPtr(gdImagePtr im, int *size);
+BGD_DECLARE(void *) gdImageAvifPtrEx(gdImagePtr im, int *size, int quality, int speed);
+BGD_DECLARE(void) gdImageAvifCtx(gdImagePtr im, gdIOCtx *outfile, int quality, int speed);
 
 /**
  * Group: GifAnim
diff --git a/src/gd_avif.c b/src/gd_avif.c
new file mode 100644
index 0000000..d8f8284
--- /dev/null
+++ b/src/gd_avif.c
@@ -0,0 +1,680 @@
+/**
+ * File: AVIF IO
+ *
+ * Read and write AVIF images using libavif (https://github.com/AOMediaCodec/libavif) .
+ * Currently, the only ICC profile we support is sRGB.
+ * Since that's what web browsers use, it's sufficient for now.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include <math.h>
+
+#include "gd.h"
+#include "gd_errors.h"
+#include "gdhelpers.h"
+#include "gd_intern.h"
+
+#ifdef HAVE_LIBAVIF
+#include <avif/avif.h>
+
+/*
+	Define defaults for encoding images:
+		CHROMA_SUBSAMPLING_DEFAULT: 4:2:0 is commonly used for Chroma subsampling.
+		CHROMA_SUBAMPLING_HIGH_QUALITY: Use 4:4:4, or no subsampling, when a sufficient high quality is requested.
+		SUBAMPLING_HIGH_QUALITY_THRESHOLD: At or above this value, use CHROMA_SUBAMPLING_HIGH_QUALITY
+		QUANTIZER_DEFAULT:
+			We need more testing to really know what quantizer settings are optimal,
+			but teams at Google have been using maximum=30 as a starting point.
+		QUALITY_DEFAULT: following gd conventions, -1 indicates the default.
+		SPEED_DEFAULT: AVIF_SPEED_DEFAULT is -1. This simply tells the AVIF encoder to use the default speed.
+*/
+
+#define CHROMA_SUBSAMPLING_DEFAULT AVIF_PIXEL_FORMAT_YUV420
+#define CHROMA_SUBAMPLING_HIGH_QUALITY AVIF_PIXEL_FORMAT_YUV444
+#define HIGH_QUALITY_SUBSAMPLING_THRESHOLD 90
+#define QUANTIZER_DEFAULT 30
+#define QUALITY_DEFAULT -1
+#define SPEED_DEFAULT AVIF_SPEED_DEFAULT
+
+// This initial size for the gdIOCtx is standard among GD image conversion functions.
+#define NEW_DYNAMIC_CTX_SIZE 2048
+
+// Our quality param ranges from 0 to 100.
+// To calculate quality, we convert from AVIF's quantizer scale, which runs from 63 to 0.
+#define MAX_QUALITY 100
+
+// These constants are for computing the number of tiles and threads to use during encoding.
+// Maximum threads are from libavif/contrib/gkd-pixbuf/loader.c.
+#define MIN_TILE_AREA (512 * 512)
+#define MAX_TILES 8
+#define MAX_THREADS 64
+
+/*** Macros ***/
+
+/*
+	From gd_png.c:
+		convert the 7-bit alpha channel to an 8-bit alpha channel.
+		We do a little bit-flipping magic, repeating the MSB
+		as the LSB, to ensure that 0 maps to 0 and
+		127 maps to 255. We also have to invert to match
+		PNG's convention in which 255 is opaque.
+*/
+#define alpha7BitTo8Bit(alpha7Bit) \
+	(alpha7Bit == 127 ? \
+				0 : \
+				255 - ((alpha7Bit << 1) + (alpha7Bit >> 6)))
+
+#define alpha8BitTo7Bit(alpha8Bit) (gdAlphaMax - (alpha8Bit >> 1))
+
+
+/*** Helper functions ***/
+
+/* Convert the quality param we expose to the quantity params used by libavif.
+	 The *Quantizer* params values can range from 0 to 63, with 0 = highest quality and 63 = worst.
+	 We make the scale 0-100, and we reverse this, so that 0 = worst quality and 100 = highest.
+
+	 Values below 0 are set to 0, and values below MAX_QUALITY are set to MAX_QUALITY.
+*/
+static int quality2Quantizer(int quality) {
+	int clampedQuality = CLAMP(quality, 0, MAX_QUALITY);
+
+	float scaleFactor = (float) AVIF_QUANTIZER_WORST_QUALITY / (float) MAX_QUALITY;
+
+	return round(scaleFactor * (MAX_QUALITY - clampedQuality));
+}
+
+/*
+	 As of February 2021, this algorithm reflects the latest research on how many tiles
+	 and threads to include for a given image size.
+	 This is subject to change as research continues.
+
+	 Returns false if there was an error, true if all was well.
+ */
+static avifBool setEncoderTilesAndThreads(avifEncoder *encoder, avifRGBImage *rgb) {
+	int imageArea, tiles, tilesLog2, encoderTiles;
+
+	// _gdImageAvifCtx(), the calling function, checks this operation for overflow
+	imageArea = rgb->width * rgb->height;
+
+	tiles = (int) ceil((double) imageArea / MIN_TILE_AREA);
+	tiles = MIN(tiles, MAX_TILES);
+	tiles = MIN(tiles, MAX_THREADS);
+
+	// The number of tiles in any dimension will always be a power of 2. We can only specify log(2)tiles.
+
+	tilesLog2 = floor(log2(tiles));
+
+	// If the image's width is greater than the height, use more tile columns
+	// than tile rows to make the tile size close to a square.
+
+	if (rgb->width >= rgb->height) {
+		encoder->tileRowsLog2 = tilesLog2 / 2;
+		encoder->tileColsLog2 = tilesLog2 - encoder->tileRowsLog2;
+	} else {
+		encoder->tileColsLog2 = tilesLog2 / 2;
+		encoder->tileRowsLog2 = tilesLog2 - encoder->tileColsLog2;
+	}
+
+	// It's good to have one thread per tile.
+	encoderTiles = (1 << encoder->tileRowsLog2) * (1 << encoder->tileColsLog2);
+	encoder->maxThreads = encoderTiles;
+
+	return AVIF_TRUE;
+}
+
+/*
+	 We can handle AVIF images whose color profile is sRGB, or whose color profile isn't set.
+*/
+static avifBool isAvifSrgbImage(avifImage *avifIm) {
+	return
+		(avifIm->colorPrimaries == AVIF_COLOR_PRIMARIES_BT709 ||
+			avifIm->colorPrimaries == AVIF_COLOR_PRIMARIES_UNSPECIFIED) &&
+		(avifIm->transferCharacteristics == AVIF_TRANSFER_CHARACTERISTICS_SRGB ||
+			avifIm->transferCharacteristics == AVIF_TRANSFER_CHARACTERISTICS_UNSPECIFIED)
+	;
+}
+
+/*
+	 Check the result from an Avif function to see if it's an error.
+	 If so, decode the error and output it, and return true.
+	 Otherwise, return false.
+*/
+static avifBool isAvifError(avifResult result, const char *msg) {
+	if (result != AVIF_RESULT_OK) {
+		gd_error("avif error - %s: %s", msg, avifResultToString(result));
+		return AVIF_TRUE;
+	}
+
+	return AVIF_FALSE;
+}
+
+
+/*
+	<readfromCtx> implements the avifIOReadFunc interface by calling the relevant functions
+	in the gdIOCtx. Our logic is inspired by avifIOMemoryReaderRead() and avifIOFileReaderRead().
+	We don't know whether we're reading from a file or from memory. We don't have to know,
+	since we rely on the helper functions in the gdIOCtx.
+	We assume we've stashed the gdIOCtx in io->data, as we do in createAvifIOFromCtx().
+
+	We ignore readFlags, just as the avifIO*ReaderRead() functions do.
+
+	If there's a problem, this returns an avifResult error.
+	If things go well, return AVIF_RESULT_OK.
+	Of course these AVIF codes shouldn't be returned by any top-level GD function.
+*/
+static avifResult readFromCtx(avifIO *io, uint32_t readFlags, uint64_t offset, size_t size, avifROData *out)
+{
+	void *dataBuf = NULL;
+	gdIOCtx *ctx = (gdIOCtx *) io->data;
+
+	// TODO: if we set sizeHint, this will be more efficient.
+
+	if (offset > LONG_MAX || size < 0)
+		return AVIF_RESULT_IO_ERROR;
+
+	// Try to seek offset bytes forward. If we pass the end of the buffer, throw an error.
+	if (!ctx->seek(ctx, offset))
+		return AVIF_RESULT_IO_ERROR;
+
+	dataBuf = gdMalloc(size);
+	if (!dataBuf) {
+		gd_error("avif error - couldn't allocate memory");
+		return AVIF_RESULT_UNKNOWN_ERROR;
+	}
+
+	// Read the number of bytes requested.
+	// If getBuf() returns a negative value, that means there was an error.
+	int charsRead = ctx->getBuf(ctx, dataBuf, size);
+	if (charsRead < 0) {
+		gdFree(dataBuf);
+		return AVIF_RESULT_IO_ERROR;
+	}
+
+	out->data = dataBuf;
+	out->size = charsRead;
+	return charsRead == size ? AVIF_RESULT_OK : AVIF_RESULT_TRUNCATED_DATA;
+}
+
+// avif.h says this is optional, but it seemed easy to implement.
+static void destroyAvifIO(struct avifIO *io) {
+	avifFree(io);
+}
+
+/* Set up an avifIO object.
+	 The functions in the gdIOCtx struct may point either to a file or a memory buffer.
+	 To us, that's immaterial.
+	 Our task is simply to assign avifIO functions to the proper functions from gdIOCtx.
+	 The destroy function needs to destroy the avifIO object and anything else it uses.
+
+	 Returns NULL if memory for the object can't be allocated.
+*/
+
+// TODO: can we get sizeHint somehow?
+static avifIO *createAvifIOFromCtx(gdIOCtx *ctx) {
+	avifIO *io;
+
+	io = gdMalloc(sizeof(*io));
+	if (io == NULL)
+		return NULL;
+
+	// TODO: setting persistent=FALSE is safe, but it's less efficient. Is it necessary?
+	io->persistent = AVIF_FALSE;
+	io->read = readFromCtx;
+	io->write = NULL; // this function is currently unused; see avif.h
+	io->destroy = destroyAvifIO;
+	io->sizeHint = 0; // sadly, we don't get this information from the gdIOCtx.
+	io->data = ctx;
+
+	return io;
+}
+
+
+/*** Decoding functions ***/
+
+/*
+	Function: gdImageCreateFromAvif
+
+		<gdImageCreateFromAvif> is called to load truecolor images from
+		AVIF format files. Invoke <gdImageCreateFromAvif> with an
+		already opened pointer to a file containing the desired
+		image. <gdImageCreateFromAvif> returns a <gdImagePtr> to the new
+		truecolor image, or NULL if unable to load the image (most often
+		because the file is corrupt or does not contain a AVIF
+		image). <gdImageCreateFromAvif> does not close the file.
+
+		This function creates a gdIOCtx struct from the file pointer it's passed.
+		And then it relies on <gdImageCreateFromAvifCtx> to do the real decoding work.
+		If the file contains an image sequence, we simply read the first one, discarding the rest.
+
+	Variants:
+
+		<gdImageCreateFromAvifPtr> creates an image from AVIF data
+		already in memory.
+
+		<gdImageCreateFromAvifCtx> reads data from the function
+		pointers in a <gdIOCtx> structure.
+
+	Parameters:
+
+		infile - pointer to the input file
+
+	Returns:
+
+		A pointer to the new truecolor image.	This will need to be
+		destroyed with <gdImageDestroy> once it is no longer needed.
+
+		On error, returns 0.
+*/
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvif(FILE *infile)
+{
+	gdImagePtr im;
+	gdIOCtx *ctx = gdNewFileCtx(infile);
+
+	if (!ctx)
+		return NULL;
+
+	im = gdImageCreateFromAvifCtx(ctx);
+	ctx->gd_free(ctx);
+
+	return im;
+}
+
+/*
+	Function: gdImageCreateFromAvifPtr
+
+		See <gdImageCreateFromAvif>.
+
+	Parameters:
+
+		size						- size of Avif data in bytes.
+		data						- pointer to Avif data.
+*/
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvifPtr(int size, void *data)
+{
+	gdImagePtr im;
+	gdIOCtx *ctx = gdNewDynamicCtxEx(size, data, 0);
+
+	if (!ctx)
+		return 0;
+
+	im = gdImageCreateFromAvifCtx(ctx);
+	ctx->gd_free(ctx);
+
+	return im;
+}
+
+/*
+	Function: gdImageCreateFromAvifCtx
+
+		See <gdImageCreateFromAvif>.
+
+		Additional details: the AVIF library comes with functions to create an IO object from
+		a file and from a memory pointer. Of course, it doesn't have a way to create an IO object
+		from a gdIOCtx. So, here, we use our own helper function, <createAvifIOfromCtx>.
+
+		Otherwise, we create the image by calling AVIF library functions in order:
+		* avifDecoderCreate(), to create the decoder
+		* avifDecoderSetIO(), to tell libavif how to read from our data structure
+		* avifDecoderParse(), to parse the image
+		* avifDecoderNextImage(), to read the first image from the decoder
+		* avifRGBImageSetDefaults(), to create the avifRGBImage
+		* avifRGBImageAllocatePixels(), to allocate memory for the pixels
+		* avifImageYUVToRGB(), to convert YUV to RGB
+
+		Finally, we create a new gd image and copy over the pixel data.
+
+	Parameters:
+
+		ctx							- a gdIOCtx struct
+*/
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvifCtx (gdIOCtx *ctx)
+{
+	int x, y;
+	gdImage *im = NULL;
+	avifResult result;
+	avifIO *io;
+	avifDecoder *decoder;
+	avifRGBImage rgb;
+
+	// this lets us know that memory hasn't been allocated yet for the pixels
+	rgb.pixels = NULL;
+
+	decoder = avifDecoderCreate();
+
+	io = createAvifIOFromCtx(ctx);
+	if (!io) {
+		gd_error("avif error - Could not allocate memory");
+		goto cleanup;
+	}
+
+	avifDecoderSetIO(decoder, io);
+
+	result = avifDecoderParse(decoder);
+	if (isAvifError(result, "Could not parse image"))
+		goto cleanup;
+
+	// Note again that, for an image sequence, we read only the first image, ignoring the rest.
+	result = avifDecoderNextImage(decoder);
+	if (isAvifError(result, "Could not decode image"))
+		goto cleanup;
+
+	if (!isAvifSrgbImage(decoder->image))
+		gd_error_ex(LOG_WARNING, "Image's color profile is not sRGB");
+
+	// Set up the avifRGBImage, and convert it from YUV to an 8-bit RGB image.
+	// (While AVIF image pixel depth can be 8, 10, or 12 bits, GD truecolor images are 8-bit.)
+	avifRGBImageSetDefaults(&rgb, decoder->image);
+	rgb.depth = 8;
+	avifRGBImageAllocatePixels(&rgb);
+
+	result = avifImageYUVToRGB(decoder->image, &rgb);
+	if (isAvifError(result, "Conversion from YUV to RGB failed"))
+		goto cleanup;
+
+	im = gdImageCreateTrueColor(decoder->image->width, decoder->image->height);
+	if (!im) {
+		gd_error("avif error - Could not create GD truecolor image");
+		goto cleanup;
+	}
+
+	im->saveAlphaFlag = 1;
+
+	// Read the pixels from the AVIF image and copy them into the GD image.
+
+	uint8_t *p = rgb.pixels;
+
+	for (y = 0; y < decoder->image->height; y++) {
+		for (x = 0; x < decoder->image->width; x++) {
+			uint8_t r = *(p++);
+			uint8_t g = *(p++);
+			uint8_t b = *(p++);
+			uint8_t a = alpha8BitTo7Bit(*(p++));
+			im->tpixels[y][x] = gdTrueColorAlpha(r, g, b, a);
+		}
+	}
+
+cleanup:
+	// if io has been allocated, this frees it
+	avifDecoderDestroy(decoder);
+
+	if (rgb.pixels)
+		avifRGBImageFreePixels(&rgb);
+
+	return im;
+}
+
+
+/*** Encoding functions ***/
+
+/*
+	Function: gdImageAvifEx
+
+		<gdImageAvifEx> outputs the specified image to the specified file in
+		AVIF format. The file must be open for writing. Under MSDOS and
+		all versions of Windows, it is important to use "wb" as opposed to
+		simply "w" as the mode when opening the file, and under Unix there
+		is no penalty for doing so. <gdImageAvifEx> does not close the file;
+		your code must do so.
+
+	Variants:
+
+		<gdImageAvifEx> writes the image to a file, encoding with the default quality and speed.
+
+		<gdImageAvifPtrEx> stores the image in RAM.
+
+		<gdImageAvifPtr> stores the image in RAM, encoding with the default quality and speed.
+
+		<gdImageAvifCtx> stores the image using a <gdIOCtx> struct.
+
+	Parameters:
+
+		im			- The image to save.
+		outFile - The FILE pointer to write to.
+		quality - Compression quality (0-100). 0 is lowest-quality, 100 is highest.
+		speed	 - The speed of compression (0-10). 0 is slowest, 10 is fastest.
+
+	Notes on parameters:
+		quality - If quality = -1, we use a default quality as defined in QUALITY_DEFAULT.
+			For information on how we convert this quality to libavif's quantity param, see <quality2Quantizer>.
+
+		speed - At slower speeds, encoding may be quite slow. Use judiciously.
+
+		Qualities or speeds that are lower than the minimum value get clamped to the minimum value,
+		abd qualities or speeds that are lower than the maximum value get clamped to the maxmum value.
+
+
+	Returns:
+
+		* for <gdImageAvifEx>, <gdImageAvif>, and <gdImageAvifCtx>, nothing.
+		* for <gdImageAvifPtrEx> and <gdImageAvifPtr>, a pointer to the image in memory.
+*/
+
+/*
+	 Function: _gdImageAvifCtx
+
+	 We need this underscored function because gdImageAvifCtx() can't return anything.
+	 And our functions that operate on a memory buffer need to know whether the encoding has succeeded.
+
+	 If we're passed the QUALITY_DEFAULT of -1, set the quantizer params to QUANTIZER_DEFAULT.
+
+	 This function returns 0 on success, or 1 on failure.
+ */
+static avifBool _gdImageAvifCtx(gdImagePtr im, gdIOCtx *outfile, int quality, int speed)
+{
+	avifResult result;
+	avifRGBImage rgb;
+	avifRWData avifOutput = AVIF_DATA_EMPTY;
+	avifBool failed = AVIF_FALSE;
+	avifBool lossless = quality == 100;
+	avifEncoder *encoder = NULL;
+
+	uint32_t val;
+	uint8_t *p;
+	uint8_t a;
+	int x, y;
+
+	if (im == NULL)
+		return 1;
+
+	if (!gdImageTrueColor(im)) {
+		gd_error("avif doesn't support palette images");
+		return 1;
+	}
+
+	if (!gdImageSX(im) || !gdImageSY(im)) {
+		gd_error("image dimensions must not be zero");
+		return 1;
+	}
+
+	if (overflow2(gdImageSX(im), gdImageSY(im))) {
+		gd_error("image dimensions are too large");
+		return 1;
+	}
+
+	if (speed != AVIF_SPEED_DEFAULT)
+		speed = CLAMP(speed, AVIF_SPEED_SLOWEST, AVIF_SPEED_FASTEST);
+
+	avifPixelFormat subsampling = quality >= HIGH_QUALITY_SUBSAMPLING_THRESHOLD ?
+		CHROMA_SUBAMPLING_HIGH_QUALITY : CHROMA_SUBSAMPLING_DEFAULT;
+
+	// Create the AVIF image.
+	// Set the ICC to sRGB, as that's what gd supports right now.
+	// Note that MATRIX_COEFFICIENTS_IDENTITY enables lossless conversion from RGB to YUV.
+
+	avifImage *avifIm = avifImageCreate(gdImageSX(im), gdImageSY(im), 8, subsampling);
+
+	avifIm->colorPrimaries = AVIF_COLOR_PRIMARIES_BT709;
+	avifIm->transferCharacteristics = AVIF_TRANSFER_CHARACTERISTICS_SRGB;
+	avifIm->matrixCoefficients = lossless ? AVIF_MATRIX_COEFFICIENTS_IDENTITY : AVIF_MATRIX_COEFFICIENTS_BT709;
+
+	avifRGBImageSetDefaults(&rgb, avifIm);
+	// this allocates memory, and sets rgb.rowBytes and rgb.pixels.
+	avifRGBImageAllocatePixels(&rgb);
+
+	// Parse RGB data from the GD image, and copy it into the AVIF RGB image.
+	// Convert 7-bit GD alpha channel values to 8-bit AVIF values.
+
+	p = rgb.pixels;
+	for (y = 0; y < rgb.height; y++) {
+		for (x = 0; x < rgb.width; x++) {
+			val = im->tpixels[y][x];
+
+			*(p++) = gdTrueColorGetRed(val);
+			*(p++) = gdTrueColorGetGreen(val);
+			*(p++) = gdTrueColorGetBlue(val);
+			*(p++) = alpha7BitTo8Bit(gdTrueColorGetAlpha(val));
+		}
+	}
+
+	// Convert the RGB image to YUV.
+
+	result = avifImageRGBToYUV(avifIm, &rgb);
+	failed = isAvifError(result, "Could not convert image to YUV");
+	if (failed)
+		goto cleanup;
+
+	// Encode the image in AVIF format.
+
+	encoder = avifEncoderCreate();
+	int quantizerQuality = quality == QUALITY_DEFAULT ?
+		QUANTIZER_DEFAULT : quality2Quantizer(quality);
+
+	encoder->minQuantizer = quantizerQuality;
+	encoder->maxQuantizer = quantizerQuality;
+	encoder->minQuantizerAlpha = quantizerQuality;
+	encoder->maxQuantizerAlpha = quantizerQuality;
+	encoder->speed = speed;
+
+	failed = !setEncoderTilesAndThreads(encoder, &rgb);
+	if (failed)
+		goto cleanup;
+
+	//TODO: is there a reason to use timeSscales != 1?
+	result = avifEncoderAddImage(encoder, avifIm, 1, AVIF_ADD_IMAGE_FLAG_SINGLE);
+	failed = isAvifError(result, "Could not encode image");
+	if (failed)
+		goto cleanup;
+
+	result = avifEncoderFinish(encoder, &avifOutput);
+	failed = isAvifError(result, "Could not finish encoding");
+	if (failed)
+		goto cleanup;
+
+	// Write the AVIF image bytes to the GD ctx.
+
+	gdPutBuf(avifOutput.data, avifOutput.size, outfile);
+
+cleanup:
+	if (rgb.pixels)
+		avifRGBImageFreePixels(&rgb);
+
+	if (encoder)
+		avifEncoderDestroy(encoder);
+
+	if (avifOutput.data)
+		avifRWDataFree(&avifOutput);
+
+	return failed;
+}
+
+BGD_DECLARE(void) gdImageAvifEx(gdImagePtr im, FILE *outFile, int quality, int speed)
+{
+	gdIOCtx *out = gdNewFileCtx(outFile);
+
+	if (out == NULL)
+		return;
+
+	gdImageAvifCtx(im, out, quality, speed);
+	out->gd_free(out);
+}
+
+BGD_DECLARE(void) gdImageAvif(gdImagePtr im, FILE *outFile)
+{
+	gdImageAvifEx(im, outFile, QUALITY_DEFAULT, AVIF_SPEED_DEFAULT);
+}
+
+BGD_DECLARE(void *) gdImageAvifPtrEx(gdImagePtr im, int *size, int quality, int speed)
+{
+	void *rv;
+	gdIOCtx *out = gdNewDynamicCtx(NEW_DYNAMIC_CTX_SIZE, NULL);
+
+	if (out == NULL) {
+		return NULL;
+	}
+
+	if (_gdImageAvifCtx(im, out, quality, speed))
+		rv = NULL;
+	else
+		rv = gdDPExtractData(out, size);
+
+	out->gd_free(out);
+	return rv;
+}
+
+BGD_DECLARE(void *) gdImageAvifPtr(gdImagePtr im, int *size)
+{
+	return gdImageAvifPtrEx(im, size, QUALITY_DEFAULT, AVIF_SPEED_DEFAULT);
+}
+
+
+BGD_DECLARE(void) gdImageAvifCtx(gdImagePtr im, gdIOCtx *outfile, int quality, int speed)
+{
+	_gdImageAvifCtx(im, outfile, quality, speed);
+}
+
+#else /* !HAVE_LIBAVIF */
+
+static void *_noAvifError(void)
+{
+	gd_error("AVIF image support has been disabled\n");
+	return NULL;
+}
+
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvif(FILE *ctx)
+{
+	return _noAvifError();
+}
+
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvifPtr(int size, void *data)
+{
+	return _noAvifError();
+}
+
+BGD_DECLARE(gdImagePtr) gdImageCreateFromAvifCtx(gdIOCtx *ctx)
+{
+	return _noAvifError();
+}
+
+BGD_DECLARE(void) gdImageAvifCtx(gdImagePtr im, gdIOCtx *outfile, int quality, int speed)
+{
+	_noAvifError();
+}
+
+BGD_DECLARE(void) gdImageAvifEx(gdImagePtr im, FILE *outFile, int quality, int speed)
+{
+	_noAvifError();
+}
+
+BGD_DECLARE(void) gdImageAvif(gdImagePtr im, FILE *outFile)
+{
+	_noAvifError();
+}
+
+BGD_DECLARE(void *) gdImageAvifPtr(gdImagePtr im, int *size)
+{
+	return _noAvifError();
+}
+
+BGD_DECLARE(void *) gdImageAvifPtrEx(gdImagePtr im, int *size, int quality, int speed)
+{
+	return _noAvifError();
+}
+
+#endif /* HAVE_LIBAVIF */
diff --git a/src/gd_filename.c b/src/gd_filename.c
index 6b67c3a..ddfaa02 100644
--- a/src/gd_filename.c
+++ b/src/gd_filename.c
@@ -51,6 +51,10 @@ static const struct FileType {
     {".xbm",    gdImageCreateFromXbm,   NULL,           NULL},
     {".tga",    gdImageCreateFromTga,   NULL,           NULL},
 
+#ifdef HAVE_LIBAVIF
+    {".avif",   gdImageCreateFromAvif,  gdImageAvif,    NULL},
+#endif
+
 #ifdef HAVE_LIBPNG
     {".png",    gdImageCreateFromPng,   gdImagePng,     NULL},
 #endif
diff --git a/src/gd_webp.c b/src/gd_webp.c
index ab15109..a0b4787 100644
--- a/src/gd_webp.c
+++ b/src/gd_webp.c
@@ -42,10 +42,10 @@
 
   Variants:
 
-    <gdImageCreateFromJpegPtr> creates an image from WebP data
+    <gdImageCreateFromWebpPtr> creates an image from WebP data
     already in memory.
 
-    <gdImageCreateFromJpegCtx> reads its data via the function
+    <gdImageCreateFromWebpCtx> reads its data via the function
     pointers in a <gdIOCtx> structure.
 
   Parameters:
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 6775948..b279f63 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -17,6 +17,7 @@ if (BUILD_TEST)
 	include_directories (BEFORE ${GD_INCLUDE_DIR} "${GDTEST_SOURCE_DIR}" "${CMAKE_BINARY_DIR}" "${CMAKE_BINARY_DIR}/tests/gdtest")
 
 	SET(TESTS_DIRS
+		avif
 		bmp
 		fontconfig
 		freetype
diff --git a/tests/Makefile.am b/tests/Makefile.am
index efbe26a..3630810 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -13,6 +13,7 @@ CLEANFILES =
 EXTRA_DIST =
 TESTS =
 
+include avif/Makemodule.am
 include bmp/Makemodule.am
 include fontconfig/Makemodule.am
 include freetype/Makemodule.am
@@ -99,6 +100,7 @@ EXTRA_DIST += \
 
 # We don't keep any media files in the top dir ... just generated outputs.
 CLEANFILES += \
+	*.avif \
 	*.bmp \
 	*.gd \
 	*.gd2 \
diff --git a/tests/avif/.gitignore b/tests/avif/.gitignore
new file mode 100644
index 0000000..66233b0
--- /dev/null
+++ b/tests/avif/.gitignore
@@ -0,0 +1,5 @@
+/avif_im2im
+/avif_null
+/avif_ptr_double_free
+/bad_input
+/compare_avif_to_png
diff --git a/tests/avif/CMakeLists.txt b/tests/avif/CMakeLists.txt
new file mode 100644
index 0000000..e2df47b
--- /dev/null
+++ b/tests/avif/CMakeLists.txt
@@ -0,0 +1,17 @@
+IF(AVIF_FOUND)
+LIST(APPEND TESTS_FILES
+	avif_ptr_double_free
+	avif_im2im
+	avif_null
+	bad_input
+)
+
+IF(PNG_FOUND)
+LIST(APPEND TESTS_FILES
+	compare_avif_to_png
+)
+ENDIF(PNG_FOUND)
+
+ENDIF(AVIF_FOUND)
+
+ADD_GD_TESTS()
diff --git a/tests/avif/Makemodule.am b/tests/avif/Makemodule.am
new file mode 100644
index 0000000..b446a93
--- /dev/null
+++ b/tests/avif/Makemodule.am
@@ -0,0 +1,16 @@
+if HAVE_LIBAVIF
+libgd_test_programs += \
+	avif/avif_ptr_double_free
+	avif/avif_im2im
+	avif/avif_null
+	avif/bad_input
+
+if HAVE_LIBPNG
+libgd_test_programs += \
+	avif/compare_avif_to_png
+endif
+
+endif
+
+EXTRA_DIST += \
+	avif/CMakeLists.txt
diff --git a/tests/avif/avif_im2im.c b/tests/avif/avif_im2im.c
new file mode 100644
index 0000000..3a07ebd
--- /dev/null
+++ b/tests/avif/avif_im2im.c
@@ -0,0 +1,67 @@
+/**
+ * File: avif_im2im
+ *
+ * Sanity check for AVIF encoding and decoding.
+ * We create a simple gd image, we encode it to AVIF, and we decode it back to gd.
+ * Then we make sure the image we started with and the image we finish with are the same.
+ *
+ */
+
+#include "gd.h"
+#include "gdtest.h"
+#include <stdio.h>
+
+int main()
+{
+	gdImagePtr srcGdIm, destGdIm;
+	void *avifImageDataPtr;
+	FILE *fp;
+	int r, g, b;
+	int size = 0;
+	CuTestImageResult result = {0, 0};
+
+	// Create new gd image and add some shapes to it.
+	srcGdIm = gdImageCreateTrueColor(100, 100);
+	gdTestAssertMsg(srcGdIm != NULL, "could not create source image\n");
+
+	r = gdImageColorAllocate(srcGdIm, 0xFF, 0, 0);
+	g = gdImageColorAllocate(srcGdIm, 0, 0xFF, 0);
+	b = gdImageColorAllocate(srcGdIm, 0, 0, 0xFF);
+	gdImageFilledRectangle(srcGdIm, 0, 0, 99, 99, r);
+	gdImageRectangle(srcGdIm, 20, 20, 79, 79, g);
+	gdImageEllipse(srcGdIm, 70, 25, 30, 20, b);
+
+	// Encode the gd image to a test AVIF file.
+	fp = gdTestTempFp();
+	gdImageAvif(srcGdIm, fp);
+	fclose(fp);
+
+	// Encode the gd image to an AVIF image in memory.
+	avifImageDataPtr = gdImageAvifPtrEx(srcGdIm, &size, 100, 10);
+	gdTestAssertMsg(avifImageDataPtr != NULL, "gdImageAvifPtr() returned null\n");
+	gdTestAssertMsg(size > 0, "gdImageAvifPtr() returned a non-positive size\n");
+
+	// Encode the AVIF image back into a gd image.
+	destGdIm = gdImageCreateFromAvifPtr(size, avifImageDataPtr);
+	gdTestAssertMsg(destGdIm != NULL, "gdImageAvifPtr() returned null\n");
+
+	// Encode that gd image to a test AVIF file.
+	fp = gdTestTempFp();
+	gdImageAvif(destGdIm, fp);
+	fclose(fp);
+
+	// Make sure the image we started with is the same as the image after two conversions.
+	 gdTestImageDiff(srcGdIm, destGdIm, NULL, &result);
+	 gdTestAssertMsg(result.pixels_changed == 0, "pixels changed: %d\n", result.pixels_changed);
+
+	if (srcGdIm)
+		gdImageDestroy(srcGdIm);
+
+	if (destGdIm)
+		gdImageDestroy(destGdIm);
+
+	if (avifImageDataPtr)
+		gdFree(avifImageDataPtr);
+
+	return gdNumFailures();
+}
diff --git a/tests/avif/avif_null.c b/tests/avif/avif_null.c
new file mode 100644
index 0000000..bbcc9c6
--- /dev/null
+++ b/tests/avif/avif_null.c
@@ -0,0 +1,23 @@
+/**
+ * File: avif_null.c
+ *
+ * Simple test case, confirming that if you try to create an AVIF image from a
+ * null file pointer, the creation will fail, and it will return NULL.
+ */
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+	gdImagePtr im;
+
+	im = gdImageCreateFromAvif(NULL);
+	if (!gdTestAssert(im == NULL))
+		gdImageDestroy(im);
+
+	gdImageAvif(im, NULL); /* noop safely */
+
+	return gdNumFailures();
+}
diff --git a/tests/avif/avif_ptr_double_free.c b/tests/avif/avif_ptr_double_free.c
new file mode 100644
index 0000000..8160950
--- /dev/null
+++ b/tests/avif/avif_ptr_double_free.c
@@ -0,0 +1,34 @@
+/**
+ * Test that failure to convert to AVIF returns NULL
+ *
+ * We are creating an image, set its width to zero, and pass this image to
+ * gdImageAvifPtr().
+ * This is supposed to fail, and as such should return NULL.
+ *
+ * See also <https://github.com/libgd/libgd/issues/381>
+ */
+
+#include "gd.h"
+#include "gdtest.h"
+
+int main()
+{
+	gdImagePtr src, dst;
+	int size;
+
+	src = gdImageCreateTrueColor(1, 10);
+	gdTestAssert(src != NULL);
+
+	src->sx = 0;  // making the width 0 should cause gdImageAvifPtr() to fail
+
+	dst = gdImageAvifPtr(src, &size);
+	gdTestAssert(dst == NULL);
+
+	if (src)
+		gdImageDestroy(src);
+
+	if (dst)
+		gdImageDestroy(dst);
+
+	return gdNumFailures();
+}
diff --git a/tests/avif/baboon.avif b/tests/avif/baboon.avif
new file mode 100644
index 0000000..f5821db
--- /dev/null
+++ b/tests/avif/baboon.avif
diff --git a/tests/avif/baboon.png b/tests/avif/baboon.png
new file mode 100644
index 0000000..fdc5dcb
--- /dev/null
+++ b/tests/avif/baboon.png
diff --git a/tests/avif/bad_input.c b/tests/avif/bad_input.c
new file mode 100644
index 0000000..a9f976b
--- /dev/null
+++ b/tests/avif/bad_input.c
@@ -0,0 +1,72 @@
+/**
+ * File: bad_input.c
+ *
+ * Make sure that the AVIF encoding and decoding functions handle bad input gracefully.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include "gd.h"
+#include "gdtest.h"
+
+#define PATH "avif/"
+#define MAX_FILEPATH_LENGTH 50
+
+#define NON_AVIF_FILE_NAME "sunset.png"
+#define AVIF_FILE_NAME "sunset.avif"
+
+int main() {
+	FILE *fp;
+	int retval;
+	char nonAvifFilePath[MAX_FILEPATH_LENGTH], avifFilePath[MAX_FILEPATH_LENGTH];
+	gdImagePtr realIm, badIm;
+	void *rv;
+	int size;
+
+// Create paths for our files.
+	strcpy(avifFilePath, PATH);
+	strcat(avifFilePath, AVIF_FILE_NAME);
+
+	strcpy(nonAvifFilePath, PATH);
+	strcat(nonAvifFilePath, NON_AVIF_FILE_NAME);
+
+// Read in an AVIF image for testing.
+
+	fp = gdTestFileOpen(avifFilePath);
+	realIm = gdImageCreateFromAvif(fp);
+	fclose(fp);
+	if (!gdTestAssertMsg(realIm != NULL, "gdImageCreateFromAvif() failed\n"))
+		return 1;
+
+// Try to decode a non-AVIF file.
+
+	fp = gdTestFileOpen(nonAvifFilePath);
+	badIm = gdImageCreateFromAvif(fp);
+	fclose(fp);
+	gdTestAssertMsg(badIm == NULL, "gdImageCreateFromAvif() failed to return NULL when passed a non-AVIF file\n");
+
+	if (badIm)
+		gdImageDestroy(badIm);
+
+ // Try to encode a valid image with bad quality parameters. This should still work.
+
+	rv = gdImageAvifPtrEx(realIm, &size, 400, 10);
+	gdTestAssertMsg(rv != NULL, "gdImageAvifPtrEx() rejected an overly high quality param instead of clamping it to a valid value");
+	gdFree(rv);
+
+	rv = gdImageAvifPtrEx(realIm, &size, -4, 10);
+	gdTestAssertMsg(rv != NULL, "gdImageAvifPtrEx() rejected a negative quality param instead of clamping it to a valid value");
+	gdFree(rv);
+
+	rv = gdImageAvifPtrEx(realIm, &size, 30, 30);
+	gdTestAssertMsg(rv != NULL, "gdImageAvifPtrEx() rejected an overly high speed param instead of clamping it to a valid value");
+	gdFree(rv);
+
+	rv = gdImageAvifPtrEx(realIm, &size, 30, -4);
+	gdTestAssertMsg(rv != NULL, "gdImageAvifPtrEx() rejected a negative speed param instead of clamping it to a valid value");
+	gdFree(rv);
+
+	gdImageDestroy(realIm);
+
+	return gdNumFailures();
+}
diff --git a/tests/avif/compare_avif_to_png.c b/tests/avif/compare_avif_to_png.c
new file mode 100644
index 0000000..716eae9
--- /dev/null
+++ b/tests/avif/compare_avif_to_png.c
@@ -0,0 +1,100 @@
+/**
+ * File: compare_avif_to_png
+ *
+ * Thorough check for AVIF encoding and decoding.
+ * This test reqiures a set of PNG images that have been losslessly encoded to AVIFs.
+ * For each such image, we encode the PNG into an AVIF, with the GD format as an intermediary,
+ * then compare the resulting AVIF with the original PNG.
+ *
+ * We then do this process in reverse, encoding the AVIF into a PNG,
+ * and compare the resulting PNG with the original AVIF.
+ *
+ * We report any discrepancies in the images, or any other errors that may occur.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include "gd.h"
+#include "gdtest.h"
+
+#define PATH "avif/"
+#define MAX_FILEPATH_LENGTH 200
+
+int main() {
+	FILE *fp;
+	gdImagePtr imFromPng = NULL, imFromAvif = NULL;
+	void *avifImDataPtr = NULL, *pngImDataPtr = NULL;
+	int size;
+	char filePath[MAX_FILEPATH_LENGTH], pngFilePath[MAX_FILEPATH_LENGTH], avifFilePath[MAX_FILEPATH_LENGTH];
+	char errMsg[MAX_FILEPATH_LENGTH + 100];
+
+	const int filesCount = 4;
+	const char *filenames[filesCount] = {"baboon", "dice_with_alpha", "plum_blossom_12bit", "sunset"};
+
+	for (int i = 0; i < filesCount; i++) {
+
+		// First, encode each PNG into an AVIF (with the GD format as an intermediary),
+		// then compare the result with the original PNG.
+
+		strcpy(filePath, PATH);
+		strcat(filePath, filenames[i]);
+		strcat(strcpy(pngFilePath, filePath), ".png");
+		strcat(strcpy(avifFilePath, filePath), ".avif");
+
+		fp = gdTestFileOpen(pngFilePath);
+		imFromPng = gdImageCreateFromPng(fp);
+		fclose(fp);
+
+		strcat(strcpy(errMsg, filenames[i]), ".png: gdImageCreateFromPng failed\n");
+		if (!gdTestAssertMsg(imFromPng != NULL, errMsg))
+			goto avif2png;
+
+		strcat(strcpy(errMsg, filenames[i]), ": gdImageAvifPtrEx failed\n");
+		avifImDataPtr = gdImageAvifPtrEx(imFromPng, &size, 100, 0);
+		if (!gdTestAssertMsg(avifImDataPtr != NULL, errMsg))
+			goto avif2png;
+
+		strcat(strcpy(errMsg, filenames[i]), ": gdImageCreateFromAvifPtr failed\n");
+		imFromAvif = gdImageCreateFromAvifPtr(size, avifImDataPtr);
+		if (!gdTestAssertMsg(imFromAvif != NULL, errMsg))
+			goto avif2png;
+
+		strcat(strcpy(errMsg, filenames[i]), ".png: Encoded AVIF image did not match original PNG\n");
+		gdTestAssertMsg(gdAssertImageEquals(imFromPng, imFromAvif), errMsg);
+
+		// Then, decode each AVIF into a GD format, and compare that with the orginal PNG.
+
+avif2png:
+		continue;
+
+/* Skip this reverse test for now, until we can find images that encode to PNGs
+	 losslessly.
+
+		fp = gdTestFileOpen(avifFilePath);
+		imFromAvif = gdImageCreateFromAvif(fp);
+		fclose(fp);
+
+		strcat(strcpy(errMsg, filenames[i]), ".avif: gdImageCreateFromAvif failed\n");
+		if (!gdTestAssertMsg(imFromAvif != NULL, errMsg))
+			continue;
+
+		strcat(strcpy(errMsg, filenames[i]), ".avif: Encoded PNG image did not match original AVIF\n");
+		gdTestAssertMsg(gdAssertImageEqualsToFile(pngFilePath, imFromAvif), errMsg);
+*/
+
+}
+
+	if (imFromPng)
+		gdImageDestroy(imFromPng);
+
+	if (imFromAvif)
+		gdImageDestroy(imFromAvif);
+
+	if (avifImDataPtr)
+		gdFree(avifImDataPtr);
+
+	if (pngImDataPtr)
+		gdFree(pngImDataPtr);
+
+	return gdNumFailures();
+}
diff --git a/tests/avif/dice_with_alpha.avif b/tests/avif/dice_with_alpha.avif
new file mode 100644
index 0000000..dce625b
--- /dev/null
+++ b/tests/avif/dice_with_alpha.avif
diff --git a/tests/avif/dice_with_alpha.png b/tests/avif/dice_with_alpha.png
new file mode 100644
index 0000000..d2809d1
--- /dev/null
+++ b/tests/avif/dice_with_alpha.png
diff --git a/tests/avif/plum_blossom_12bit.avif b/tests/avif/plum_blossom_12bit.avif
new file mode 100644
index 0000000..7959d15
--- /dev/null
+++ b/tests/avif/plum_blossom_12bit.avif
diff --git a/tests/avif/plum_blossom_12bit.png b/tests/avif/plum_blossom_12bit.png
new file mode 100644
index 0000000..e6901e2
--- /dev/null
+++ b/tests/avif/plum_blossom_12bit.png
diff --git a/tests/avif/sunset.avif b/tests/avif/sunset.avif
new file mode 100644
index 0000000..4964558
--- /dev/null
+++ b/tests/avif/sunset.avif
diff --git a/tests/avif/sunset.png b/tests/avif/sunset.png
new file mode 100644
index 0000000..21f45d5
--- /dev/null
+++ b/tests/avif/sunset.png
diff --git a/travis/main.sh b/travis/main.sh
index 2d29b5d..9965c40 100755
--- a/travis/main.sh
+++ b/travis/main.sh
@@ -78,6 +78,9 @@ build_autotools() {
 	m distclean
 }
 
+# TODO: When we switch to Ubuntu 21+ (Hirsute), we can reenable libavif coverage,
+# as Ubuntu 21+ supports libavif 0.8.2+.
+#	"-DENABLE_AVIF=1"
 cmake_args=(
 	"-DBUILD_SHARED_LIBS=1"
 	"-DBUILD_STATIC_LIBS=1"
@@ -94,7 +97,7 @@ cmake_args=(
 )
 
 # libxpm-dev is unavaible in brew repo
-# Once it gets avaible, please modify this code block.
+# Once it gets available, please modify this code block.
 if [[ ${TRAVIS_OS_NAME} == "linux" ]]; then
 	cmake_args+=("-DENABLE_XPM=1")
 fi
diff --git a/windows/Makefile.vc b/windows/Makefile.vc
index d97b22f..3fefe80 100644
--- a/windows/Makefile.vc
+++ b/windows/Makefile.vc
@@ -95,10 +95,11 @@ LIB_OBJS= \
   $(LIBGD_OBJ_DIR)\gd_crop.obj \
   $(LIBGD_OBJ_DIR)\gd_color_map.obj \
   $(LIBGD_OBJ_DIR)\gd_heif.obj \
+  $(LIBGD_OBJ_DIR)\gd_avif.obj \
   $(LIBGD_OBJ_DIR)\gd_webp.obj
 
 LIBS=kernel32.lib ole32.lib user32.lib advapi32.lib shell32.lib ws2_32.lib Dnsapi.lib Gdi32.Lib
-LIBS_GD=libjpeg_a.lib freetype_a.lib libpng_a.lib libiconv_a.lib  zlib_a.lib libheif_a.lib libwebp_a.lib libxpm_a.lib libtiff.lib
+LIBS_GD=libjpeg_a.lib freetype_a.lib libpng_a.lib libiconv_a.lib  zlib_a.lib libheif_a.lib libwebp_a.lib libxpm_a.lib libavif_a.lib libtiff.lib
 
 PROG_EXES= \
 	$(LIBGD_OBJ_DIR)\gdcmpgif.exe \
@@ -135,11 +136,13 @@ CFLAGS= $(CFLAGS) \
        /DHAVE_FT2BUILD_H=1\
        /DHAVE_GD_H=1\
        /DHAVE_ICONV_H=1\
+       /DHAVE_LIBAVIF=1\
        /DHAVE_LIBFREETYPE=1\
        /DHAVE_LIBJPEG=1\
        /DHAVE_LIBPNG=1\
        /DHAVE_LIBWEBP=1\
        /DHAVE_LIBHEIF=1\
+       /DHAVE_LIBAVIF=1\
        /DHAVE_LIBZ=1\
        /DHAVE_LIBXPM=1\
        /DHAVE_LIBTIFF=1\
@@ -186,6 +189,9 @@ make_dirs:
 	@echo #ifndef HAVE_ICONV_H>> $(GD_CONFIG_H)
 	@echo #define HAVE_ICONV_H>> $(GD_CONFIG_H)
 	@echo #endif>> $(GD_CONFIG_H)
+	@echo #ifndef HAVE_LIBAVIF>> $(GD_CONFIG_H)
+	@echo #define HAVE_LIBAVIF>> $(GD_CONFIG_H)
+	@echo #endif>> $(GD_CONFIG_H)
 	@echo #ifndef HAVE_LIBFREETYPE>> $(GD_CONFIG_H)
 	@echo #define HAVE_LIBFREETYPE>> $(GD_CONFIG_H)
 	@echo #endif>> $(GD_CONFIG_H)
@@ -201,6 +207,9 @@ make_dirs:
 	@echo #ifndef HAVE_LIBHEIF>> $(GD_CONFIG_H)
 	@echo #define HAVE_LIBHEIF>> $(GD_CONFIG_H)
 	@echo #endif>> $(GD_CONFIG_H)
+	@echo #ifndef HAVE_LIBAVIF>> $(GD_CONFIG_H)
+	@echo #define HAVE_LIBAVIF>> $(GD_CONFIG_H)
+	@echo #endif>> $(GD_CONFIG_H)
 	@echo #ifndef HAVE_LIBZ>> $(GD_CONFIG_H)
 	@echo #define HAVE_LIBZ>> $(GD_CONFIG_H)
 	@echo #endif>> $(GD_CONFIG_H)
diff --git a/windows/Makefiletest.vc b/windows/Makefiletest.vc
index 827a4e7..6e5d598 100644
--- a/windows/Makefiletest.vc
+++ b/windows/Makefiletest.vc
@@ -1,5 +1,10 @@
 TESTS=bmp\bmp_im2im \
 bmp\bmp_null \
+avif\avif_ptr_double_free \
+avif\avif_im2im \
+avif\avif_null \
+avif\compare_avif_to_png \
+avif\bad_input \
 freetype\bug00132 \
 gd\gd_im2im \
 gd\gd_null \
diff --git a/windows/msys/Makefile b/windows/msys/Makefile
index 8c5d380..d183ac2 100644
--- a/windows/msys/Makefile
+++ b/windows/msys/Makefile
@@ -98,7 +98,8 @@ gd_topal.c gd_wbmp.c gdcache.c gdfontg.c gdfontl.c gdfontmb.c		\
 gdfonts.c gdfontt.c gdft.c gdhelpers.c gdkanji.c gdtables.c gdxpm.c	\
 wbmp.c gd_filter.c gd_nnquant.c gd_rotate.c gd_matrix.c				\
 gd_interpolation.c gd_crop.c gd_webp.c gd_heif.c gd_tiff.c gd_tga.c	\
-gd_bmp.c gd_xbm.c gd_color_match.c gd_version.c gd_filename.c
+gd_bmp.c gd_xbm.c gd_color_match.c gd_version.c gd_filename.c \
+gd_avif.c
 
 OBJ=$(SRC:.c=.o)