Re: [Qemu-devel] [RfC PATCH 2/3] sdl2: add support for display rendering using opengl.

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> >>> +    glBegin(GL_QUADS);
> >>> +    glTexCoord2f(0, 1);  glVertex3f(-1, -1, 0);
> >>> +    glTexCoord2f(0, 0);  glVertex3f(-1, 1, 0);
> >>> +    glTexCoord2f(1, 0);  glVertex3f(1, 1, 0);
> >>> +    glTexCoord2f(1, 1);  glVertex3f(1, -1, 0);
> >>> +    glEnd();
> >> I've been trained to hate direct mode, but it should be fine for just
> >> this quad.
> > --verbose please.  Guess for longer sequences it would be much more
> > efficient to compile this into a shader program?
> 
> Well, again, I'm used to OpenGL 3/4 Core now which doesn't have the 
> immediate mode any more. [ ... ]

> [ ... ] and maybe for some 
> reason there are people which want to use qemu with OpenGL acceleration 
> on a pre OpenGL 2 machine.

For virtio-gpu we'll need OPENGL 3 anyway, so I don't feel like caring
too much about old opengl versions.  How would the opengl 3/4 version of
the above would look like?

> >> Using glTexSubImage2D() would give us the advantage of being able to
> >> perform partial updates on the texture; but it seems to fit pretty bad
> >> into the existing code. To make it fit, I'd call glTexSubImage2D()
> >> directly in sdl2_gl_update() and just draw the quad here.
> > Yes, that should work.

Done, also factoring this into helper functions so gtk can use this too
some day, new series sent out, please have a look.

thanks,
  Gerd