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.

1 files changed, 4 insertions, 1 deletions

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