update README

CMakeLists.txt

@@ -72,7 +72,7 @@ endif()
 
 macro(plugin_option optionVariableName displayName defaultEnabled defaultPlugin)
     option(WITH_${optionVariableName} "Build ${displayName}" ${defaultEnabled})
-    option(WITH_${optionVariableName}_PLUGIN "Build ${displayName} as a plugin" ${defaultPlugin})
+    option(WITH_${optionVariableName}_PLUGIN "Build ${displayName} as a plugin" ${defaultPlugin} AND WITH_${optionVariableName})
 endmacro()
 
 macro(plugin_compilation_info optionVariableName detectionVariable displayName)

README.md

@@ -26,10 +26,13 @@ libheif has support for:
 * decoding of files while downloading (e.g. extract image size before file has been completely downloaded)
 
 Supported codecs:
-* HEIC: libde265, x265, kvazaar
-* AVIF: libaom, dav1d, rav1d, svt-av1
-* JPEG: libjpeg
-* JPEG-2000: OpenJPEG
+| Format       |  Decoders        |  Encoders      |
+|:-------------|:----------------:|:--------------:|
+| HEIC         | libde265, ffmpeg | x265, kvazaar  |
+| AVIF         | AOM, dav1d       | rav1d, svt-av1 |
+| JPEG         | libjpeg          | libjpeg        |
+| JPEG2000     | OpenJPEG         | OpenJPEG       |
+| uncompressed | builtin          | builtin        |
 
 ## API
 
@@ -113,9 +116,11 @@ There is also an experimental Go API, but this is not stable yet.
 
 This library uses the CMake build system (the earlier autotools build files have been removed in v1.16.0).
 
+For a minimal configuration, we recommend to use the codecs libde265 and x265 for HEIC and AOM for AVIF.
 Make sure that you compile and install [libde265](https://github.com/strukturag/libde265)
 first, so that the configuration script will find this.
-Also install x265 and its development files if you want to use HEIF encoding.
+Also install x265 and its development files if you want to use HEIF encoding, but note that x265 is GPL.
+An alternative to x265 is kvazaar (BSD).
 
 The basic build steps are as follows:
 
@@ -136,7 +141,35 @@ There are CMake presets to cover the most frequent use cases.
 * `fuzzing`: similar to `testing`, this builds the fuzzers. The library should not distributed.
 
 You can optionally adapt these standard configurations to your needs.
-This can be done, for example, by calling `ccmake ..` from within the `build` directory.
+This can be done, for example, by calling `ccmake .` from within the `build` directory.
+
+### CMake configuration variables
+
+Libheif supports many different codecs. In order to reduce the number of dependencies and the library size,
+you can choose which of these codecs to include. Each codec can be compiled either as built-in to the library
+with a hard dependency, or as a separate plugin file that is loaded dynamically.
+
+For each codec, there are two configuration variables:
+
+* `WITH_{codec}`: enables the codec
+* `WITH_{codec}_PLUGIN`: when enabled, the codec is compiled as a separate plugin.
+
+In order to use dynamic plugins, also make sure that `ENABLE_PLUGIN_LOADING` is enabled.
+
+Further options are:
+
+* `WITH_UNCOMPRESSED_CODEC`: enable support for uncompressed images according to ISO/IEC 23001-17:2023. This is *experimental*
+   and not available as a dynamic plugin.
+* `WITH_DEFLATE_HEADER_COMPRESSION`: enables support for compressed metadata. When enabled, it adds a dependency to `zlib`.
+   Note that header compression is not widely supported yet.
+* `WITH_LIBSHARPYUV`: enables high-quality YCbCr/RGB color space conversion algorithms (requires `libsharpyuv`,
+   e.g. from the `third-party` directory).
+* `ENABLE_MULTITHREADING_SUPPORT`: can be used to disable any multithreading support, e.g. for embedded platforms.
+* `ENABLE_PARALLEL_TILE_DECODING`: when enabled, libheif will decode tiled images in parallel to speed up compilation.
+* `PLUGIN_DIRECTORY`: the directory where libheif will search for dynamic plugins when the environment
+  variable `LIBHEIF_PLUGIN_PAT` is not set.
+* `WITH_REDUCED_VISIBILITY`: only export those symbols into the library that are public API.
+  Has to be turned off for running the tests.
 
 ### macOS