SDL2 works differnetly with widget from code or from ui file

[kepeter]

I succeeded to connect SDL2 to a widget using code, but when using a winId of a widget coming from the ui (designer) it works only partially...

file:///home/peter/Pictures/Screenshots/Screenshot%20from%202023-05-14%2007-13-32.png

It is obvious that that SDL2 did connect to the top widget (otherwise it wasn't painted black), but the red rectangle (that bouncing left-to-right) shows only on the bottom one.

The top comes from the ui (designer) and the bottom from the code...

Extract from the ui file:

<widget class="QWidget" name="centralwidget">
   <layout class="QGridLayout" name="gridLayout">
    <item row="0" column="0">
     <widget class="QGraphicsView" name="graphicsView"/>
    </item>
   </layout>
  </widget>

The code adds the second widget (in the constructor of the main window):

ui->setupUi(this);

view = new QGraphicsView();
ui->gridLayout->addWidget(view);

The code binds the widgets to SDL2:

void MainWindow::SDLInit() {
    SetWindow1(SDL_CreateWindowFrom((void *)ui->graphicsView->winId()));
    SetWindow2(SDL_CreateWindowFrom((void *)view->winId()));
    SetRenderer1(SDL_CreateRenderer(GetWindow1(), -1, SDL_RENDERER_SOFTWARE));
    SetRenderer2(SDL_CreateRenderer(GetWindow2(), -1, SDL_RENDERER_SOFTWARE));
}

I really would like to understand the difference here...

[Kent-Dorfman]

@kepeter

Because you are breaking the framework by managing the widget window independently of the Qt framework. All bets are off when you reference a section of screen real-estate via an X11 winID instead of using the Qt primitives.

There are a "few" legitimate reasons to do this, such as assigning a media player visual to a Qt widget window, but don't expect to rely upon the framework behaving well WRT the shared window region.

FWIW, the QWidget::autoFillBackground gives some minor control over you the widget is painted but it isn't a fix.

I would ask the 10,000$ question of why you feel you must use SDL in a Qt window in the first place.

[kepeter]

@Kent-Dorfman
That does not explain the difference... Both windows are passed to SDL2, but only one fully works, the other only partially, and nobody screams about...

[JonB]

@kepeter said in SDL2 works differnetly with widget from code or from ui file:

I really would like to understand the difference here...

uic preprocesses the .ui file into ui_....h file in the build output directory. That is the complete C++ code, compare that against your own case which works till you find the difference.

[SGaist]

Hi,

Do you have any SDL error checking done in your code ?
There might be useful information there.