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Edit the dosbox configuration file and change aspect=0 to aspect=1, it'll resize the output to be aspect correct but it might be a bit blurry (IIRC the scale3x

by Crinus 7y ago

Edit the dosbox configuration file and change aspect=0 to aspect=1, it'll resize the output to be aspect correct but it might be a bit blurry (IIRC the scale3x scaler will do a pixel-scale and then that will be bilinearly resized, giving mostly crispy pixels with a bit of in-between bleeding which is probably the best you can get with an LCD monitor)

susam 7y ago
With aspect=1, the square is 400 pixels high and 384 pixels wide, not exactly an aspect ratio of 1:1 but quite close, 1.04:1. The parent of my earlier comment, i.e., the one by klodolph, claims that the pixel aspect ratio would be square by default in DOSBox, so I thought I would verify it once. As per my experiments, that does not seem to be the case.
- fireattack 7y ago
  I think what he meant is that, The pixels are square in DOSBox, but the graphics from these old programs are designed for non-square pixel ratio. So, if you display it with square pixel, the display aspect ratio will be wrong. (Of course, this still contradicts with what neatcoder said, but I can't remember if these programs were "squished" on CRTs or not.)
  - susam 7y ago
    See these screenshots of SCREEN 2 in GW-BASIC running in DOSBox: - https://imgur.com/NZUGL1e https://imgur.com/NZUGL1e (aspect=0) - https://imgur.com/rnQOfA4 https://imgur.com/rnQOfA4 (aspect=1) The one with aspect=1 looks very odd.
    - klodolph 7y ago
      The one with aspect=1 looks incorrectly configured. There are a number of different graphics modes, they have different pixel aspect ratios, you can also adjust the monitor, it is possible that back in school you were using a different mode or a different monitor. I think there are some other factors that can affect this.
      - susam 7y ago
        Back in school, I played with SCREEN 0, SCREEN 1, and SCREEN 2 documented in the GW-BASIC user manual. Here's a copy: http://www.antonis.de/qbebooks/gwbasman/screens.html http://www.antonis.de/qbebooks/gwbasman/screens.html . The reason why I stick to aspect=0 (the DOSBox default) is that this is the one that more closely reproduces the experience I had with the CRT monitors at school. I agree that the actual monitor or the way it is configured could affect the aspect ratio we observe. Perhaps ours was not adjusted to produce 1:1 square while working with IBM Logo. But it did produce 1:1 square with GW-BASIC SCREEN 1 mode.
        klodolph 7y ago
        CGA/EGA/VGA is supposed to have a pixel aspect ratio of 1:1.2 in 320x200 mode. If you adjusted the monitor to give 1:1 square pixels, then this was unusual.
        susam 7y ago
        I think I know why the screenshot for SCREEN mode looks odd with aspect=1. The documentation at https://www.dosbox.com/wiki/Dosbox.conf https://www.dosbox.com/wiki/Dosbox.conf mentions, > Do aspect correction. It only affects non-square pixel modes like VGA Mode 13h, which has a resolution of 320x200 pixels and is used by many DOS games (DOOM, etc). However SCREEN 2 mode of GW-BASIC has a resolution of 640x200 ( http://www.antonis.de/qbebooks/gwbasman/screens.html http://www.antonis.de/qbebooks/gwbasman/screens.html ).
        klodolph 7y ago
        That mode is also non-square, with an aspect of 0.6:1. The IBM PC and its various video cards in the early days used a number of tricks to keep the cost down, one of those tricks is to keep the horizontal and vertical sync signals the same for different modes as much as possible. (Recently I’ve started to appreciate just how many tricks they used to keep the cost down, without sacrificing hardware reliability in the process!) For both 320x200 and 640x200, HSYNC ran at 15.75 kHz, VSYNC ran at 60 Hz. When you go from 320x200 to 640x200, all that happens is the pixel clock (the rate at which you read out from RAM) is doubled, so you get exactly two pixels horizontally packed in where there used to be one pixel. The older hardware, like EGA video cards, can only generate one other HSYNC speed: 21.8 kHz, for special 350-line modes. When VGA came out, it doubled the HSYNC frequency and, for these modes, would just read each row out twice. http://www.minuszerodegrees.net/video/bios_video_modes.htm http://www.minuszerodegrees.net/video/bios_video_modes.htm So SCREEN 1 should have 1.2:1 ratio, and SCREEN 2 should have a 0.6:1 ratio. One of the better ways to verify this kind of thing is to compare box art from DOS video games to screenshots taken from DOSBox or sprites extracted from the data files. You can see that the screenshots from DOSBox match the sprite files, if you leave aspect unadjusted, but if you look at the box art from the retail packaging, you will (often) see artwork and screenshots with the correct aspect ratio, just like you see on real hardware. Here's a DOOM Wiki page discussing it, with a number of pictures and sources: https://doom.fandom.com/wiki/Aspect_ratio https://doom.fandom.com/wiki/Aspect_ratio
- klodolph 7y ago
  This is a misinterpretation of the experiment results. By default, aspect=false. This gives incorrect results, as you observed, with Logo producing a squashed circle and square. The fix is aspect=true (or aspect=1). This gives correct results, with non-square aspect for pixels, with Logo producing a more correct circle and square. Because the Logo implementation was written for an actual IBM PC or compatible, it assumes that the aspect ratio of a 320x200 pixel screen is about 4:3. However, when displayed with the incorrect square-pixel aspect ratio given by default in DOSBox, it will be 8:5. In other words, DOSBox displays graphics with a square pixel ratio by default, which is different from the original hardware. If you wrote a DOS program to draw a square number of pixels, say 128x128, then you would see that in DOSBox it would also be square, but on real hardware it would be about 20% taller than it is wide. If you use Logo you will get the opposite results, because Logo is correctly designed for the original hardware.

by Crinus 7y ago

susam 7y ago

With aspect=1, the square is 400 pixels high and 384 pixels wide, not exactly an aspect ratio of 1:1 but quite close, 1.04:1. The parent of my earlier comment, i.e., the one by klodolph, claims that the pixel aspect ratio would be square by default in DOSBox, so I thought I would verify it once. As per my experiments, that does not seem to be the case.

fireattack 7y ago
I think what he meant is that, The pixels are square in DOSBox, but the graphics from these old programs are designed for non-square pixel ratio. So, if you display it with square pixel, the display aspect ratio will be wrong. (Of course, this still contradicts with what neatcoder said, but I can't remember if these programs were "squished" on CRTs or not.)
- susam 7y ago
  See these screenshots of SCREEN 2 in GW-BASIC running in DOSBox: - https://imgur.com/NZUGL1e https://imgur.com/NZUGL1e (aspect=0) - https://imgur.com/rnQOfA4 https://imgur.com/rnQOfA4 (aspect=1) The one with aspect=1 looks very odd.
  - klodolph 7y ago
    The one with aspect=1 looks incorrectly configured. There are a number of different graphics modes, they have different pixel aspect ratios, you can also adjust the monitor, it is possible that back in school you were using a different mode or a different monitor. I think there are some other factors that can affect this.
    - susam 7y ago
      Back in school, I played with SCREEN 0, SCREEN 1, and SCREEN 2 documented in the GW-BASIC user manual. Here's a copy: http://www.antonis.de/qbebooks/gwbasman/screens.html http://www.antonis.de/qbebooks/gwbasman/screens.html . The reason why I stick to aspect=0 (the DOSBox default) is that this is the one that more closely reproduces the experience I had with the CRT monitors at school. I agree that the actual monitor or the way it is configured could affect the aspect ratio we observe. Perhaps ours was not adjusted to produce 1:1 square while working with IBM Logo. But it did produce 1:1 square with GW-BASIC SCREEN 1 mode.
      - klodolph 7y ago
        CGA/EGA/VGA is supposed to have a pixel aspect ratio of 1:1.2 in 320x200 mode. If you adjusted the monitor to give 1:1 square pixels, then this was unusual.
        susam 7y ago
        I think I know why the screenshot for SCREEN mode looks odd with aspect=1. The documentation at https://www.dosbox.com/wiki/Dosbox.conf https://www.dosbox.com/wiki/Dosbox.conf mentions, > Do aspect correction. It only affects non-square pixel modes like VGA Mode 13h, which has a resolution of 320x200 pixels and is used by many DOS games (DOOM, etc). However SCREEN 2 mode of GW-BASIC has a resolution of 640x200 ( http://www.antonis.de/qbebooks/gwbasman/screens.html http://www.antonis.de/qbebooks/gwbasman/screens.html ).
        klodolph 7y ago
        That mode is also non-square, with an aspect of 0.6:1. The IBM PC and its various video cards in the early days used a number of tricks to keep the cost down, one of those tricks is to keep the horizontal and vertical sync signals the same for different modes as much as possible. (Recently I’ve started to appreciate just how many tricks they used to keep the cost down, without sacrificing hardware reliability in the process!) For both 320x200 and 640x200, HSYNC ran at 15.75 kHz, VSYNC ran at 60 Hz. When you go from 320x200 to 640x200, all that happens is the pixel clock (the rate at which you read out from RAM) is doubled, so you get exactly two pixels horizontally packed in where there used to be one pixel. The older hardware, like EGA video cards, can only generate one other HSYNC speed: 21.8 kHz, for special 350-line modes. When VGA came out, it doubled the HSYNC frequency and, for these modes, would just read each row out twice. http://www.minuszerodegrees.net/video/bios_video_modes.htm http://www.minuszerodegrees.net/video/bios_video_modes.htm So SCREEN 1 should have 1.2:1 ratio, and SCREEN 2 should have a 0.6:1 ratio. One of the better ways to verify this kind of thing is to compare box art from DOS video games to screenshots taken from DOSBox or sprites extracted from the data files. You can see that the screenshots from DOSBox match the sprite files, if you leave aspect unadjusted, but if you look at the box art from the retail packaging, you will (often) see artwork and screenshots with the correct aspect ratio, just like you see on real hardware. Here's a DOOM Wiki page discussing it, with a number of pictures and sources: https://doom.fandom.com/wiki/Aspect_ratio https://doom.fandom.com/wiki/Aspect_ratio
klodolph 7y ago
This is a misinterpretation of the experiment results. By default, aspect=false. This gives incorrect results, as you observed, with Logo producing a squashed circle and square. The fix is aspect=true (or aspect=1). This gives correct results, with non-square aspect for pixels, with Logo producing a more correct circle and square. Because the Logo implementation was written for an actual IBM PC or compatible, it assumes that the aspect ratio of a 320x200 pixel screen is about 4:3. However, when displayed with the incorrect square-pixel aspect ratio given by default in DOSBox, it will be 8:5. In other words, DOSBox displays graphics with a square pixel ratio by default, which is different from the original hardware. If you wrote a DOS program to draw a square number of pixels, say 128x128, then you would see that in DOSBox it would also be square, but on real hardware it would be about 20% taller than it is wide. If you use Logo you will get the opposite results, because Logo is correctly designed for the original hardware.