Re: [PATCH] ui/sdl2: Allow high-dpi

[Antonio Caggiano]

Hi Marc-André,

On 07/06/2023 12:21, Marc-André Lureau wrote:
> Hi Antonio
>
> On Wed, Jun 7, 2023 at 1:05 PM Antonio Caggiano <quic_acaggian@quicinc.com>
> wrote:
>
> > Add the SDL_WINDOW_ALLOW_HIGHDPI flag when creating a window and get the
> > drawable size instead of the window size when setting up the framebuffer
> > and the viewport.
> What does this actually change?

The sdl2-gl backend does not work properly on high-DPI windows. [0]
My understanding is that by allowing high-DPI, SDL creates a framebuffer 
with the right size in pixels which might be different than the size of 
the window. [1]
I believe we just need to use the framebuffer size for GL viewport and 
texture, by retrieving it with SDL_GL_GetDrawableSize.

> What about non-gl display, Mouse motion, and display resize?

From what I can see by testing the SDL2 renderer, it seems to handle 
all of this transparently, so there is nothing we need to do in sdl2-2d.

Same for mouse motion, which I believe is using window "screen coordinates".

Display resize is a bit weird for a bunch of frames, but then it fixes 
itself.

[0] 
https://user-images.githubusercontent.com/6058008/244368628-329241dc-267d-452f-b8ce-816ae1623131.png
[1] https://wiki.libsdl.org/SDL2/SDL_GetWindowSize#remarks

> thanks
>
> Signed-off-by: Antonio Caggiano <quic_acaggian@quicinc.com>
> > ---
> >   ui/sdl2-gl.c | 4 ++--
> >   ui/sdl2.c    | 2 +-
> >   2 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/ui/sdl2-gl.c b/ui/sdl2-gl.c
> > index bbfa70eac3..251b7d56d6 100644
> > --- a/ui/sdl2-gl.c
> > +++ b/ui/sdl2-gl.c
> > @@ -53,7 +53,7 @@ static void sdl2_gl_render_surface(struct sdl2_console
> > *scon)
> >       SDL_GL_MakeCurrent(scon->real_window, scon->winctx);
> >       sdl2_set_scanout_mode(scon, false);
> >
> > -    SDL_GetWindowSize(scon->real_window, &ww, &wh);
> > +    SDL_GL_GetDrawableSize(scon->real_window, &ww, &wh);
> >       surface_gl_setup_viewport(scon->gls, scon->surface, ww, wh);
> >
> >       surface_gl_render_texture(scon->gls, scon->surface);
> > @@ -239,7 +239,7 @@ void sdl2_gl_scanout_flush(DisplayChangeListener *dcl,
> >
> >       SDL_GL_MakeCurrent(scon->real_window, scon->winctx);
> >
> > -    SDL_GetWindowSize(scon->real_window, &ww, &wh);
> > +    SDL_GL_GetDrawableSize(scon->real_window, &ww, &wh);
> >       egl_fb_setup_default(&scon->win_fb, ww, wh);
> >       egl_fb_blit(&scon->win_fb, &scon->guest_fb, !scon->y0_top);
> >
> > diff --git a/ui/sdl2.c b/ui/sdl2.c
> > index 9d703200bf..c9c83815ca 100644
> > --- a/ui/sdl2.c
> > +++ b/ui/sdl2.c
> > @@ -95,7 +95,7 @@ void sdl2_window_create(struct sdl2_console *scon)
> >       }
> >   #ifdef CONFIG_OPENGL
> >       if (scon->opengl) {
> > -        flags |= SDL_WINDOW_OPENGL;
> > +        flags |= SDL_WINDOW_OPENGL | SDL_WINDOW_ALLOW_HIGHDPI;
> >       }
> >   #endif
> >
> > --
> > 2.40.0

Cheers,
Antonio