How to build and use an SDK for QT

The OpenSTLinux distribution offers the possibility to generate examples of images based on the QT framework (st-example-image-qt and, for ecosystem release ≥ v2.1.0 , st-example-image-qtwayland) as demonstrators, not for developing products.

This article provides information on how to create the SDK for building QT applications based on the example images above.

1 Prerequisites

Being able to rebuild an OpenSTLinux image

2 OpenSTLinux QT images and SDK

OpenSTLinux distribution provides two examples of images based on 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 and will be displayed in full-screen mode.

To build the images and the associated SDK, the first step requires installing the OpenSTLinux distribution through the steps listed in chapter Installing the OpenSTLinux distribution.

2.1 QT image and SDK with weston/wayland

This image and SDK will use QTwayland backend to run QT applications in independent windows managed by weston. It 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

and read and accept EULA. Further details are available in Initializing the OpenEmbedded build environment.

Then build the image and the SDK

 bitbake st-example-image-qtwayland
 bitbake st-example-image-qtwayland -c populate_sdk

Further details are available in Generating your own Starter and Developer Packages and How to create an SDK for OpenSTLinux distribution.

Note: the legacy command bitbake meta-toolchain-qt5 is not suggested 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 in folder tmp-glibc/deploy/sdk/. It can be installed as described in Run the SDK installation script, with the 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

This image and SDK will use QT backend to run a single QT applications in fullscreen mode.

Initialize the OpenEmbedded build environment for the openstlinux-eglfs distro

 DISTRO=openstlinux-eglfs MACHINE=stm32mp1 source layers/meta-st/scripts/envsetup.sh

and read and accept EULA. Further details are available in Initializing the OpenEmbedded build environment.

Then build the image and the SDK

 bitbake st-example-image-qt
 bitbake st-example-image-qt -c populate_sdk

Further details are available in Generating your own Starter and Developer Packages and How to create an SDK for OpenSTLinux distribution.

Note: the legacy command bitbake meta-toolchain-qt5 is not suggested 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 in folder tmp-glibc/deploy/sdk/. It can be installed as described in Run the SDK installation script, with the 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 Select display resolution and size in EGLFS

When using a display that accepts multiple resolutions, it is possible to specify the preferred resolution 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 will expand the application to run it in full screen. This can produce blurred images on the display and can impact the system performance.

It is possible to configure QT 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 QT configuration

By default, QT internal data uses 64 bit per pixel (16 bit for each R, G, B, A components). It is possible to slightly improve the performance by forcing QT to use 32 bit per pixel (8 bit 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

-QT_CONFIG_FLAGS += " -no-sse2 -no-opengles3"
+QT_CONFIG_FLAGS += " -no-sse2 -no-opengles3 -no-feature-raster-64bit"

Note: the above setup can produce visible artefacts, so has to be evaluated case by case.

4 Build a QT application

Enter in 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