MiSTer FPGA Forum

mapf wrote: ↑Thu Oct 14, 2021 4:48 pm Scandoubler and vga_scaler are two functions that are independent. Scandoubling turns the 15kHz TV-compatible signal into a 31kHz VGA CRT-compatible signal. In order to use your monitor, scandoubling is sufficient.

The scaler works on the image produced by the core and scales it to fit into a fixed resolution. It is normally active on the HDMI output. The vga_scaler option activates it also on the analog output. I is an option when the scandoubled image cannot be displayed by your crt monitor, or when you want to play a "tate" mode arcade game on your horizontally oriented CRT.

Both functions can be active at the same time, but they interfere with each other. The scandoubler doubles the vertical resolution of the image, and depending on the input and output resolution, integer scaling might no longer be possible - then you either have a very small image on the screen or need to use non-integer scaling, which has visual artifacts.

Regarding your question on filters and scandoubler fx: Filters work on the scaled image, the fx change the behaviour of the scandoubler.

As for recommendations: With a VGA CRT, using the scandoubler with 25% black lines looks very similar to a high-quality PWM monitor image. If you want to try more elaborate filters, disable the scandoubler and use a high resolution (like 1280×960) video mode with the vga_scaler active.

FoxbatStargazer wrote: ↑Thu Oct 14, 2021 11:58 pm 1) You must use scandoubler *IF* using "original" analog output (vga_scaler=0 on the VGA port, of direct_video=1 on an HDMI->VGA adapter.)

2) vga_scaler=1 will let you use the scaler on the VGA port, so you can turn scandoubler off. It will use whatever resolution in your video_mode.

3) Varies based on what your monitor can do. For horizontal scanline filters I would say you want at least a 3x vertical scale for them to be visible, and 4x delivers better quality. If you want absolute best results you can customize to an integer multiple for each core (example: 1280x89y for Genesis), or for a more generic pick you can use a "superwide" resolution (like 1920x976), with any kind of interpolation you won't notice horizontal scaling artifacts as you are probably pushing past your monitor's effective TVL. See note 5 about the aspect ratio though.

4) Don't know about C64 in particular but some NTSC cores draw around 244p instead of 240p. Sometimes there is some kind of border/cropping setting in the core menu's video settings that reduces this area to like 224p so it can scale better. If not something like 976p (244x4) might be a safer value for integer scaling. You can make your own resolutions with a custom video mode.

5) the scaler assumes you are using an LCD display with square pixels, so 1280x720 would be a 16:9 display, and default "normal" scaling uses black borders on the sides to have the active image be around 4:3. A CRT monitor compresses the pixel width to be 4:3 anyway so in these cases, in the core menu video options set aspect ratio to "full" or "wide" and it will effectively remove the side borders and the monitor will squish it to appear correct.

A simple setting for DOS is something like 1920x400, that gives you perfect 6x width for 320x200 games, and enough pixels so the 720x400 DOS text isn't garbled. Make sure refresh rate is set to be variable and vsync_adjust=1 or 2 though, because 400p typically won't show on a VGA monitor unless you are at least 70hz. If you are using WIndows I would try to match your video mode to the resolution you are emulating.