[Gambas-user] gb3 (rev. 3641) and SDL surfaces

[Benoît Minisini]

> I've been experimenting with gb.sdl and found that I could achieve frame
> rates higher than 380 fps at 1920x1080, including alpha channel. This
> involves writing directly to the SDL window/surface with a 1920x1080
> image loaded from a file, for example:
> 
> Public Screen As New Window As "Screen"
> Public SomeImage As Image = Image.Load("someimage.png")
> 
> Public Sub Main()
> 
>    ' Create screen.
>    With Screen
>      .Width = 1920
>      .Height = 1080
>      .Framerate = 1000
>      .FullScreen = True
>      .Show()
>    End With
> 
> End
> 
> Public Sub Screen_Draw()
> 
>    Draw.Image(SomeImage, 0, 0)
>    Draw.Text(Screen.Framerate & " FPS", 0, 0)
> 
> End
> 
> While this is awesome, there is a problem if images need to be
> composited before being written to the SDL surface. For example, if I
> wanted to do something like this:
> 
> Water.Draw(WaterRipples, 0, 0)
> Water.Draw(SkyReflection, 0, 0)
> Water.DrawAlpha(WaterDepth, 0, 0)
> 
> and then draw Water to the SDL window, not only is the imlib2 component
> required (otherwise it states the .Draw method is unknown), it kills the
> frame rate because the Draw method is done in software (imlib2) and only
> the writes done directly to the SDL window are hardware accelerated.
> 
> Attempting to circumvent this I created a second SDL window, hoping I
> could write the contents of window B to window A. The idea was to create
> multiple secondary SDL windows, using them as image buffers, then write
> the buffers as necessary to the main SDL window when its Draw event was
> called. This didn't work at all and I don't think it's supported.
> 
> Is there a way to use the Draw method, or an equivalent, so that
> image-to-image writes can be done entirely in SDL? I've already
> converted my app to use the SDL component but too much of it currently
> uses the .Draw and .DrawAlpha methods which bring the framerate to 21
> fps at 1280x720. The framerate is only going to get worse from here, as
> I'm just getting started.

I think (only Laurent can confirm) that SDL uses internally OpenGL to do its 
stuff. So the speed of the SDL component depends on the graphics driver (which 
is a very sensible thing on Linux).

Then, if you want to compose images, I think only doing direct OpenGL call 
will help you, by stacking textured rectangles. But I don't know if OpenGL can 
do the equivalent of Draw.Alpha().

Regards,

-- 
Benoît Minisini