I have tested some of the settings for scale and aspect=true, with vgaonly and without. Scaler only appears to effect how the game is displayed to the player but does not effect the actual screen capture. A great example of this would be Dungeon Master 2, svga_s3 with scaler=hq3x. Even though the game window is scaled 3x and some of the graphics have the edges softened for the hq part, the screen capture is still 320x200, 8 bit color.
Aspect=true scales the game window to 640x480, but if coupled with vgaonly still yields 640x400 - 24 bit color captures. I haven't tested too many other combinations because I feel I have found out what I needed to know. I thought it may have been something I had done.
This all started when I was working on Lost City of Atlantis but I didn't take the time to resolve it then. I have an example which might help explain one of the situations I have run into. Since using your tutorial (
), it allowed me to pick up on a very simple and organized way of getting my DOSBox games in one place, finally. I don't want the DOSBox icon for everything so I started making icons from captures. Now this is why it is a "problem".
The attachment shows the final icon, a capture of the title, a capture of the graphic for an in-between level change, the same graphic with a palette swap and a capture of aspect=true. All of the captures were done with the vgaonly setting except the aspect=true, which was a screen capture with alt+prntscrn. The aspect=true capture was done this way to show the size of the game display reflected 640x480, even though the DOSBox capture was 640x400 - 24 bit.
This game, Cool World, is set up so that any keypress advances gameplay. While on the title screen, a keypress will bring up the options screen, blocking the graphic. With vgaonly, you grab a capture but with 24 bit color. The Title screen contains the same 256 color palette as the level screen, but the level screen was captured while it was beginning to dim after pressing ALT+F5 for the capture.
If you take both captures, resize them to 320x200, save their respective 256 color palette after decreasing from 16 million colors, the colors saved are not the same. And as far as indexes go, if you substitute the title palette for the level palette and maintain indexes, the mess you see in the level w/ title pal picture is what you get. If you substitute and choose nearest color match, it will just display the same dimmed level picture, with the colors slightly dimmer. Without vgaonly, the palette can be swapped from title to level and you get the full brightness back.
The reason behind wanting a reliable indexed palette in this example was simple. It saved time. To make the icon, I wanted the title pic of the woman with the actual graphic text for 'Cool World'. The choice was to try and cut out the text then repair the places where her hands covered the letters, or get a clean shot of the text. The clean shot was afforded by the level capture, but with the inherent color palette problem only IF the palette was 24 bit and not the original 8 bit.
So on a case by case basis, I don't think every combination of configurations could be covered with just one post. I was just trying to figure this out for myself and then share the vgaonly caveat to anyone else who might be affected by it.
@Japo: Your tutorial was very well written. I didn't need to read it all but I was able to scan for just the bits I needed, which I feel is a key element to any good reference source.
Thank you!