[Scummvm-tracker] [ScummVM :: Bugs] #16820: OpenGL Even Pixels/Pixel Perfect Scaling produces uneven pixel rows in text/glyphs

[ScummVM :: Bugs]

#16820: OpenGL Even Pixels/Pixel Perfect Scaling produces uneven pixel rows in
text/glyphs
-----------------------+---------------------------------------
Reporter:  DennyThray  |      Owner:  (none)
    Type:  defect      |     Status:  new
Priority:  normal      |  Component:  --Unset--
 Version:              |   Keywords:  pixel perfect, even pixel
    Game:              |
-----------------------+---------------------------------------
 ScummVM version:
 Version: ScummVM 2026.2.0 (Mar 28 2026 20:10:59)
 Using SDL backend with SDL 2.26.2
 Features compiled in: Vorbis FLAC MP3 RGB zLib MPEG2 FluidSynth MikMod
 Theora VPX AAC A/52 FreeType2 FriBiDi JPEG PNG GIF taskbar TTS cloud
 libcurl SDL_net ENet SDL2 TinyGL OpenGL (with shaders) RetroWave

 Game:
 Reproduced in multiple supported games. Screenshots attached from King's
 Quest VI.

 Game language:
 English

 Game version:
 [DOS CD / DOS floppy / etc.]

 Graphics settings:
 Graphics mode: OpenGL
 Render mode: <default>
 Stretch mode: Even pixels scaling
 Scaler: Normal, 2x
 Shader: None
 Aspect ratio correction: Off
 Fullscreen mode: Off
 Filter graphics: Off
 V-Sync: Off

 Issue:
 When using OpenGL with Even Pixels Scaling, pixel rows in text/glyphs are
 not rendered evenly. This is especially visible in pixel fonts. Individual
 rows of pixels in letters appear thicker or thinner than adjacent rows,
 creating a muddy/uneven appearance.

 This occurs even in windowed mode, with aspect ratio correction disabled,
 filtering disabled, no shader, and Windows DPI scaling override set to
 Application.

 Expected behavior:
 With Even Pixels Scaling, pixels should be scaled uniformly. Pixel font
 glyphs should have consistent row/column thickness, with no uneven
 stretching of individual scanlines.

 Actual behavior:
 Some glyph rows are visibly thicker than others. The artifact is easy to
 see in text. For example, in the attached screenshots, compare the
 lowercase "s" and period characters. In one screenshot the bottom row of
 the "s" appears uneven/thickened; in another, the middle/top row appears
 too wide instead.

 This does not appear to be normal fullscreen scaling, filtering, or aspect
 correction. It remains visible in non-fullscreen mode.

 Steps to reproduce:
 1. Launch ScummVM.
 2. Set Graphics mode to OpenGL.
 3. Set Stretch mode to Even pixels scaling.
 4. Set Scaler to Normal, 2x.
 5. Disable Aspect ratio correction.
 6. Disable Fullscreen mode.
 7. Disable Filter graphics.
 8. Set Shader to None.
 9. Launch a supported low-resolution pixel-art game with pixel font text,
 such as King's Quest VI.
 10. Trigger dialogue text and inspect the rendered pixel font.

 Result:
 Text glyphs show uneven pixel row thickness despite Even Pixels Scaling.

 Notes:
 This appears reproducible across multiple games I have tried, so it may be
 an OpenGL renderer/scaler issue rather than a game-specific engine issue.
-- 
Ticket URL: <https://bugs.scummvm.org/ticket/16820>
ScummVM :: Bugs <https://bugs.scummvm.org>
ScummVM