[Scummvm-tracker] [ScummVM] #9643: SDL2: Graphic issues with bilinear filtering enabled

[Lothar Serra Mari]

#9643: SDL2: Graphic issues with bilinear filtering enabled
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Reporter:  rootfather  |      Owner:
    Type:  defect      |     Status:  new
Priority:  normal      |  Component:  --Unset--
Keywords:              |       Game:
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 Note: This bug seems to be related with #9592.

 OS: Windows 10
 ScummVM: currently at f7381c2, but happens with all versions that include
 SDL2+filtering
 GPU: AMD Radeon HD 6320 [integrated solution]

 I noticed that when I enable the linear filtering feature in fullscreen
 mode, on my Windows system, it seems that the image is about 1px too small
 on each side and the image starts to 'wrap around'. See the attached
 screenshot from 'Myst', it should be much clearer than my explanation.

 Basically, it seems that the linear filter uses image data from the last
 pixel column on the right side to draw/fill/interpolate the image data of
 the first pixel column on the left side (and the same going on with the
 top and the bottom). This does *not* happen when you turn off the linear
 filtering.

 criezy couldn't reproduce the issue on his system. After some poking
 around in the source code from my side, criezy suggested to insert the
 lines
 {{{
 SDL_SetHint(SDL_HINT_RENDER_DRIVER, "direct3d11")
 }}}
 or
 {{{
 SDL_SetHint(SDL_HINT_RENDER_DRIVER, "opengl")
 }}}
 right before the call of SDL_CreateRenderer in line 2622 of surfacesdl-
 graphics.cpp.

 First, I tried direct3d11. It really works like a charm, it fixes this bug
 and even resolves #9592. The downside of this is that direct3d11 support
 in SDL is pretty new (from 2015), and we don't know how it behaves on
 older SDL2 versions or unsupported Windows versions (although I think
 DirectX 11 is supported in Windows XP SP3 and higher). Will it just ignore
 the setting and do a fallback to the first supported driver? Will it
 segfault? Will it kill your hamster? We have to investigate this.

 Next, I tried opengl. Using OpenGL solved this issue, but #9592 is
 persisting, although the rendering artefacts in the launcher changed the
 location. While both direct3d11 and opengl have a good ingame-performance,
 it is interesting to see that opengl has a better performance when
 switching between scalers (like 2x->3x and vice versa).

 Because using direct3d11 solves both issues for me, I would opt for using
 this if there are no unwanted side-effects with older versions of SDL2 or
 Windows or even with other operating systems. In case we can't use
 direct3d11 due to non-existing fallback mechanisms, opengl seems to be a
 good solution too (but then, we have to care about #9592 again).

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Ticket URL: <https://bugs.scummvm.org/ticket/9643>
ScummVM <https://bugs.scummvm.org>
ScummVM