Merge "Add doc for image_generator"
diff --git a/README.md b/README.md
index bd1cf7d..5ab19d1 100644
--- a/README.md
+++ b/README.md
@@ -143,3 +143,17 @@
Both of the two conditions need to be satisfied. Although `ro.adb.secure` is a runtime property, its
value is set at build time (written into `/prop.default`). It defaults to `1` on `-user` builds, and
`0` for other build variants. The value is overridable via `PRODUCT_DEFAULT_PROPERTY_OVERRIDES`.
+
+Localization of the background texts
+------------------------------------
+
+The recovery image supports localization of several background texts, e.g. installing, error,
+factory reset warnings, etc. For devices using `xxhdpi` and `xxxhdpi`, the build system generates
+these localization images dynamically since android-10 when building the recovery image. While
+the static images under res-*dpi/images/ is used for other display resolutions and as a
+backup.
+
+Check the invocation of the image_generator tool in the [makefile]. And the detailed usage of the
+image_generator is documented [here](./tools/image_generator/README.md).
+
+[makefile]: https://android.googlesource.com/platform/build/+/refs/heads/master/core/Makefile#1800
diff --git a/tools/image_generator/README.md b/tools/image_generator/README.md
index 5d70354..1230ad5 100644
--- a/tools/image_generator/README.md
+++ b/tools/image_generator/README.md
@@ -19,3 +19,13 @@
4. `resourceDirectory`: The resource directory that contains all the translated
strings in xml format, e.g. bootable/recovery/tools/recovery_l10n/res/
5. `outputFilename`: Path to the generated image.
+
+# Locales
+Supported locales and background texts are located in
+[tools/recovery_l10n/res/](../recovery_l10n/res/values). For each background text, the tool renders
+a localized image for every supported locale.
+
+Each individual localized image contains an encoded locale header string, and the rendered
+background text. The locale header string is generated by `Locale.forLanguageTag`. And sample
+result include `en-US`, `zh-CN`, etc. These individual images are then concatenated together to
+form the final resource image that locates in res/images, e.g. `install_text.png`