update the readme

Signed-off-by: M. Fatih Cırıt <[email protected]>

ansible/roles/qt5ct_setup/README.md

@@ -2,27 +2,71 @@
 
 ## Overview
 
-The `qt5ct_setup` Ansible role automates the configuration of the `qt5ct` environment for Autoware. It ensures `qt5ct` is installed, configures the `qt5ct` settings, updates the QSS file paths, and ensures the correct Autoware directory is used.
+The `qt5ct_setup` Ansible role automates the configuration of the `qt5ct` environment for Autoware.
+It won't affect the system-wide configuration.
 
 ## Installation
 
+Follow the instructions below to **install** or **update** the custom theme for `RViz2` in Autoware.
+
+> **Important:** Both steps must be completed during the initial installation and when you want to update the theme.
+
+
 ### Install ansible collections
 
 ```bash
 cd ~/autoware # The root directory of the cloned repository
 ansible-galaxy collection install -f -r "ansible-galaxy-requirements.yaml"
 ```
 
-This step should be repeated when a new playbook is added.
+This step should be repeated when you want to update the theme.
 
 ### Run the playbook
 
 ```bash
 ansible-playbook autoware.dev_env.install_rviz_theme  --ask-become-pass
 ```
 
-This will download and extract the artifacts to the specified directory and validate the checksums.
+This will install the custom theme for `RViz2` in Autoware.
+
+## How to use the custom theme in RViz2
+
+To apply a custom theme to RViz2, you can use the `qt5ct` platform theme. Follow these steps to ensure that the `QT_QPA_PLATFORMTHEME` environment variable is set correctly for your RViz2 instance when used with Autoware.
+
+### Manual setup for running RViz2
+
+Before running RViz2 manually, set the `QT_QPA_PLATFORMTHEME` environment variable to `qt5ct`.
+This ensures that the custom theme settings are applied.
+
+```bash
+export QT_QPA_PLATFORMTHEME=qt5ct
+```
+
+Then, start RViz2 as usual.
+
+```bash
+rviz2
+```
 
-## Usage
+### Automatic setup in Autoware
+
+In Autoware, the `QT_QPA_PLATFORMTHEME` environment variable is automatically set within the main [autoware.launch.xml](https://github.com/autowarefoundation/autoware_launch/blob/main/autoware_launch/launch/autoware.launch.xml) file.
+Therefore, you do not need to manually set this environment variable when launching Autoware.
+
+In the `autoware.launch.xml` file, RViz2 is configured with the following `<node>` element:
+
+```xml
+<node
+  pkg="rviz2"
+  exec="rviz2"
+  name="rviz2"
+  output="screen"
+  args="-d $(var rviz_config) -s $(find-pkg-share autoware_launch)/rviz/image/autoware.png"
+  if="$(var rviz)"
+  respawn="$(var rviz_respawn)">
+  <env name="QT_QPA_PLATFORMTHEME" value="qt5ct"/>
+</node>
+```
 
-Include the `qt5ct_setup` role in your playbook. Ensure your playbook includes the `autoware` directory and the required files (`base-qt5ct.conf` and `autoware.qss`) in the appropriate locations.
+This configuration automatically sets the `QT_QPA_PLATFORMTHEME` to `qt5ct` when RViz2 is launched as part of Autoware.
+It also includes additional options such as respawn behavior and custom RViz2 configurations.