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SFML development / Providing own WindowImpl backend?

« on: October 27, 2023, 07:02:04 pm »

Hi there.
I am currently trying to adapt SFML for rendering with EGL on raspberry, and it requires OpenGL ES
which are supported by SFML, but there's a small nuance:
- its initializing it in different way, than in other example that using DRM mode for creating context..
Basically with SFML the OpenGL ES gives me this:

OpenGL ES 2.x information:
  version: "2.1 Mesa 20.3.5"
  shading language version: "1.20"
  vendor: "Broadcom"
  renderer: "V3D 4.2"

But with kmscube example, i have this:

OpenGL ES 2.x information:
  version: "OpenGL ES 3.1 Mesa 20.3.5"
  shading language version: "OpenGL ES GLSL ES 3.10"
  vendor: "Broadcom"
  renderer: "V3D 4.2"

This is of course unfortunate, that when creating context using SFML library i cannot get 3.1 feature set.

So, my question whether it is possible to "extend" SFML library by providing own custom implementation of WindowImpl,
which will create & initialize system resources in proper way.
I don't wanna hack inside the library itself, is there a clean way to do that at all?

I would like to have something like that:

class MyWindowImpl : ....
class MyContextImpl : ...

int main() {
...

sf::RenderWindow<MyWindowImpl, MyContextImpl> myWindow( ... );
,,,
myWindow.draw(...)
}

Is there a way how to do that without hacking the library source code itself?
If so, it would be nice if you can provide some guidance.

Because i found it is determining WindowImpl in the library itself, and it is nailed down to platform-specific ifdefs..

for context:
#elif defined(SFML_OPENGL_ES)

#include <SFML/Window/EglContext.hpp>
using ContextType = sf::priv::EglContext;

and similarly for window:

#if defined(SFML_USE_DRM)

#include <SFML/Window/DRM/WindowImplDRM.hpp>
using WindowImplType = sf::priv::WindowImplDRM;

It would be nice to make it extensible, i.e.
using template arguments for specific context and window implementation class, and provide the above configuration
as a convenient defaults, but in case, like mine, for those who would like to create/initialize context & window using own way,
provide own implementation..

How hard it would be to do ?