Extra bottom line on native screens, chipset feature or WinUAE?

[PeterK]

When I tried to display a PAL HiRes Interlaced screen optimal on my FullHD monitor (1920x1080) and first set the size to 724x540 I expected that it could be scaled with a factor of 2.0 exactly, but it did not.

Using WinUAE 4.2.1 64 bit. D3D11, Automatic Scaling and Aspect Ratio Correction 16:9 are enabled, but that's not the point.

I noticed that on all native screens I get an additional gray scanline on the bottom which is also counted for computing the scaling factor. So when I set the PAL overscan height to 270 lines, the display gets finally 271 (542 interlaced) lines and the scaling factors are 1.989637 and 1.992620. That sometimes causes bad looking text characters, for example.

Display Size: 724x540 Offset: 6x18
First: 35 Last: 305 MinV: 31 MaxV: 313 Min: 26
POS (0 0 1920 1080) - (0 0 960 540)[960,540] (-112 18) S=1920*1080 B=752*574
8 -1 2 2
-> -736.000000 576.000000 768.000000 -572.000000 2.000000 2.000000
Display Size: 724x540 Offset: 2x18
First: 35 Last: 305 MinV: 34 MaxV: 312 Min: 26
POS (0 0 1920 1080) - (0 0 960 540)[960,540] (-116 18) S=1920*1080 B=752*574
12 -1 2 2
-> -728.000000 576.000000 776.000000 -572.000000 2.000000 2.000000
SNDRATE 312.5*227.0*50.000282=3546895.024776
PAL mode lace V=50.0003Hz H=15625.0879Hz (227x312+1) IDX=10 (PAL) D=0 RTG=0/0
Display Size: 724x542 Offset: 2x18
First: 35 Last: 306 MinV: 34 MaxV: 313 Min: 26
POS (0 0 1920 1080) - (0 0 965 542)[965,542] (-118 18) S=1920*1080 B=752*574
11 -2 2 2
-> -726.217590 575.867126 769.989624 -567.896667 1.989637 1.992620

With an overscan height of only 269 the display size is really 724x540 and the scaling works correctly with 2.0.

Display Size: 724x538 Offset: 6x18
First: 35 Last: 304 MinV: 31 MaxV: 313 Min: 26
POS (0 0 1920 1080) - (0 0 956 538)[956,538] (-110 18) S=1920*1080 B=752*574
8 0 2 2
-> -739.079529 576.133789 771.213379 -576.133789 2.008368 2.007435
Display Size: 724x538 Offset: 2x18
First: 35 Last: 304 MinV: 34 MaxV: 312 Min: 26
POS (0 0 1920 1080) - (0 0 956 538)[956,538] (-114 18) S=1920*1080 B=752*574
12 0 2 2
-> -731.046021 576.133789 779.246887 -576.133789 2.008368 2.007435
SNDRATE 312.5*227.0*50.000282=3546895.024776
PAL mode lace V=50.0003Hz H=15625.0879Hz (227x312+1) IDX=10 (PAL) D=0 RTG=0/0
Display Size: 724x540 Offset: 2x18
First: 35 Last: 305 MinV: 34 MaxV: 313 Min: 26
POS (0 0 1920 1080) - (0 0 960 540)[960,540] (-116 18) S=1920*1080 B=752*574
12 -1 2 2
-> -728.000000 576.000000 776.000000 -572.000000 2.000000 2.000000

So, for the PAL screens I can fix this issue by just using 269 overscan lines, but I can't change the overscan height for monitor drivers like Xtreme (1280x1024), and only reducing their screenmode height to 720 or 718 interlaced lines doesn't help.

There always appears this additional gray line at the bottom, except for the case that I move the display rectangle down in the overscan settings, which makes 270 lines with a correct scaling possible, but the lowest interlaced line doesn't appear and the last but one is flickering. (Disable utilities like BlackBorder.)

Is this gray bottom line a chipset feature or caused by WinUAE (even v3.0.0 shows it)? Is it required to display this line and send it to the graphics card?

[Toni Wilen]

It is correct. Interlaced modes always have odd number of lines and due to some odd chipset feature, last line (interlaced or not) is always blank and drawn in background color. (Except if A1000!)

[PeterK]

But could you make an option in WinUAE to suppress it on the display and not to send it to the graphics card?

[Toni Wilen]

Not going to happen. Line is there in hardware level and it is normal scanline like any other scanline and it can have background color changes. PAL or NTSC mode is not a programmed mode where number of scanlines can change.

Why not just set manual 2x scale and move the display so that last line is not visible? Or at least automatic integer scale so that there is no scaling artifacts.

[Photon]

How does this work?

1. Display > Native: Fullscreen, 1920x1080

2. Host > Filter > Null Filter and 2x scaling?

I have a 1920x1080 monitor and here it looks fine with no extra line.

If you change resolution of the monitor, you're in the hands of the monitor scaling chip.

[PeterK]

Originally Posted by Toni Wilen

Not going to happen.

Ok, I can live with it, but an option would have been nice.

Why not just set manual 2x scale and move the display so that last line is not visible? Or at least automatic integer scale so that there is no scaling artifacts.

Already tried that and many other filter settings, but nothing seems to work. I'm using the OS 3.1.4 WBPattern checkerboard background and that always shows scaling artifacts. Maybe it's caused by the Intel UHD Graphics 600 chip or driver, but I thought that in this case the scaling should be done by WinUAE, because I'm using Fullscreen and Native resolution (1920x1080).

@Photon
Can you post a "Display" and "Filter" screenshot or your config file, please. Thx.