The OpenSTLinux distribution enables the generation of example images based on the QT framework (st-example-image-qt and, for ecosystem release ≥ v2.1.0 
, st-example-image-qtwayland) for demonstration purposes, not for developing products.
This article provides information on how to create the SDK for building QT applications based on the above example images.
1. Prerequisites[edit source]
Be able to rebuild an OpenSTLinux image
2. OpenSTLinux QT images and SDK[edit source]
OpenSTLinux distribution provides two examples of images based on the QT framework:
- st-example-image-qtwayland (requires 'openstlinux-weston' distro and ecosystem release ≥ v2.1.0 ): thanks to weston window management, QT applications are displayed in independent windows and can coexist on the same screen with other non-QT applications;
- st-example-image-qt (requires 'openstlinux-eglfs' distro): only one QT application can access the screen. It is displayed in full-screen mode.
To build the images and the associated SDK, first install the OpenSTLinux distribution by following the procedure described in chapter Installing the OpenSTLinux distribution.
2.1. QT image and SDK with weston/wayland[edit source]
The QT image and SDK use QTwayland back-end to run QT applications in independent windows managed by weston. This requires ecosystem release ≥ v2.1.0 .
Initialize the OpenEmbedded build environment for the openstlinux-weston distro:
DISTRO=openstlinux-weston MACHINE=stm32mp1 source layers/meta-st/scripts/envsetup.sh
Read and accept EULA. Refer to Initializing the OpenEmbedded build environment for further details.
Then build the image and the SDK:
bitbake st-example-image-qtwayland bitbake st-example-image-qtwayland -c populate_sdk
Refer to Generating your own Starter and Developer Packages and How to create an SDK for OpenSTLinux distribution for further details.
Note: the legacy command bitbake meta-toolchain-qt5 is not recommended because the resulting SDK would miss some target packages.
The image can be flashed on the target board as in Flashing the built image.
The generated SDK is available in the tmp-glibc/deploy/sdk/ folder. It can be installed as described in Run the SDK installation script, using the following command:
./tmp-glibc/deploy/sdk/st-example-image-qtwayland-openstlinux-weston-stm32mp1-x86_64-toolchain-3.1-snapshot.sh -y -d <working directory absolute path>/Developer-Package/SDK
2.2. QT image and SDK with EGLFS[edit source]
The QT image and SDK use QT back-end to run single QT applications in full-screen mode.
Initialize the OpenEmbedded build environment for the openstlinux-eglfs distro:
DISTRO=openstlinux-eglfs MACHINE=stm32mp1 source layers/meta-st/scripts/envsetup.sh
Read and accept EULA. Refer to Initializing the OpenEmbedded build environment for further details.
Then build the image and the SDK:
bitbake st-example-image-qt bitbake st-example-image-qt -c populate_sdk
Refer to Generating your own Starter and Developer Packages and How to create an SDK for OpenSTLinux distribution for further details.
Note: the legacy command bitbake meta-toolchain-qt5 is not recommended because the resulting SDK would miss some target packages.
The image can be flashed on the target board as in Flashing the built image.
The generated SDK is available in the tmp-glibc/deploy/sdk/ folder. It can be installed as described in Run the SDK installation script, using the following command:
./tmp-glibc/deploy/sdk/st-example-image-qt-openstlinux-eglfs-stm32mp1-x86_64-toolchain-3.1-snapshot.sh -y -d <working directory absolute path>/Developer-Package/SDK
2.2.1. Selecting the display resolution and size in EGLFS[edit source]
When using a display that accepts multiple resolutions, the preferred resolution can be specified by editing the board file /usr/share/qt5/cursor.json. For example, for an HDMI display, change the line
{ "name": "HDMI1", "mode": "1280x720" },
and enter one of the valid resolutions reported by the command
modetest
If the current display resolution is higher than the resolution requested by the QT application, QT expands the application to run it in full screen. This can produce blurred images on the display and can impact the system performance.
The QT framework can be configured to use only one part of the overall display. For example, to use only an area of 400x300 pixels, add:
{ "name": "HDMI1", "mode": "1280x720", "size": "400x300" },
3. Configuring the QT framework[edit source]
By default, QT internal data use 64 bits per pixel (16 bits for each R, G, B and A component). The performance can be slightly improved by forcing the QT framework to use 32 bits per pixel (8 bits for each component). This can be achieved by editing the file layers/meta-st/meta-st-openstlinux/recipes-qt/qt5/qtbase_git.bbappend before the build and replacing the line
QT_CONFIG_FLAGS += " -no-sse2 -no-opengles3"
with
QT_CONFIG_FLAGS += " -no-sse2 -no-opengles3 -no-feature-raster-64bit"
Note: the above setup can produce visible artefacts and has to be evaluated on a case by case basis.
4. Building a QT application[edit source]
Open the folder that contains the application, enable the QT SDK and compile the application:
cd <path_of_app> . <install_path_sdk>/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi qmake && make