Black area at bottom of emulator

[Jestin 4]

I've mostly been ignoring this, but I get a black area at the bottom of the emulator whenever I set the screen mode to 320x200@256C.  Everything runs fine, as if the black area is simply not part of the screen.  However, when I look at other people's demos, I never see this black area.  I'm starting to worry it will be there on the actual hardware and not just the emulator.

When I have an application that only runs this code:

    lda #$80
    sec
    jsr screen_set_mode

Here is what I see:

Is this expected for some reason, or am I doing something wrong?

[StephenHorn 61]

No, that seems correct. Same thing happens to me when I do SCREEN $80.

I can't speak for everyone, but my demos do not run in 320x200@256C. My demos leave the VERA at 640x480 scale, and takes advantage of the VERA's multiple layers and sprites at that "resolution".

@SlithyMatt's Chase Vault's title screen scales the screen to 320x240 resolution, and configures VERA layer 0 to be a 320-wide 4bpp bitmap. Gameplay leaves the global scaling and layer 0 configured like this, and configures layer 1 to a 128x128 tilemap using 16x16x4bpp tiles.

Edited June 28 by StephenHorn

[SlithyMatt 125]

I think this is correct for the emulator, which is fixed at a 640x480 display, and just doubles the pixels when you pick a mode that is 320 pixels wide. @Frank van den Hoef might be able to tell you if 320x200 mode can output to an appropriate monitor in full screen with the actual hardware.

[StephenHorn 61]

I doubt the VERA is capable of swapping to an entirely different VGA resolution. Also, it appears that none of the scaling settings will allow the VERA to cleanly present a 200 pixel height. The closest you can get is a DC_VSCALE of 54, which shows 202.5 pixels, or 53, which shows 198.75 pixels. In the end, it might be worth suggesting that the kernal use DC_VSTART and DC_VSTOP to limit the drawn area and center in on the display. If maintaining something close to the original 4:3 aspect ratio is desired, it might also consider DC_VSCALE of 56, which isn't a clean multiple of 2 but draws 210 pixels height, which could then be trimmed appropriately.

Edit: Here's what DC_SCALE 56,  DC_VSTART 6, DC_VSTOP 234 looks like, blown up 2X:

Versus a 320x240 scale, but seeing VSTART and VSTOP to 20 and 220 so there's a 200-high display area:

Edited June 29 by StephenHorn

[Frank van den Hoef 11]

The hardware really only has one output resolution: 640x480. 320x200 isn't a resolution that is natively supported by VERA. As far as I know the kernal has this 320x200 resolution as part of the GEOS drawing code, which Michael didn't yet update to make use of the full 240 lines height. As Stephon Horn showed, you can use the scaling to make the 200 lines cover (almost) the full 480 output lines, but it will give some scaling artifacts.