Filter overscan setting causes HAM artifacts

Rotareneg · 27 December 2019, 16:17

When rendering an overscanned HAM display, HAM artifacts are visible on the left edge if the image is cropped off by the filter overscan settings. Is this an expected result or a bug?

I was under the impression that the filter settings were entirely a post-processing thing that happened to the video data that the emulated computer output, sort of like a virtual monitor, but it actually seems to crop the data before even HAM "decompression" happens.

Screenshots taken in WinUAE with "Take screenshot before filtering" show what is happening, with the first image using filter overscan set to Fullscreen (Max) and the second with overscan on Default:

Toni Wilen · 29 December 2019, 16:10

It shouldn't happen and I can't duplicate it. Could you include your config file + bootable adf or statefile that shows the problem?

Rotareneg · 30 December 2019, 04:55

It is related to the size of the WinUAE display: With an 800x600 window everything is fine, but at 1024x768 the image scales differently and the HAM artifacts appear. It also seems to happen at any full screen resolution, from 640x480 on up. Attached is a config and savestate with an overscan HAM image being displayed. Just change the window size between 800x600 and 1024x768 and it should happen.

Also included are logs, in case it's something specific to my system.

Toni Wilen · 30 December 2019, 14:38

Thanks. Now I see it, it probably only can happen if HAM uses overscan. HAM not being fully visible is handled correctly normally but in this case horizontal "blanking" is extended too far which breaks it. Not yet sure how to fix it.

27 December 2019, 16:17	#1
Rotareneg Registered User Join Date: Sep 2017 Location: Kansas, USA Posts: 328	Filter overscan setting causes HAM artifacts When rendering an overscanned HAM display, HAM artifacts are visible on the left edge if the image is cropped off by the filter overscan settings. Is this an expected result or a bug? I was under the impression that the filter settings were entirely a post-processing thing that happened to the video data that the emulated computer output, sort of like a virtual monitor, but it actually seems to crop the data before even HAM "decompression" happens. Screenshots taken in WinUAE with "Take screenshot before filtering" show what is happening, with the first image using filter overscan set to Fullscreen (Max) and the second with overscan on Default:

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29 December 2019, 16:10	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,534	It shouldn't happen and I can't duplicate it. Could you include your config file + bootable adf or statefile that shows the problem?

30 December 2019, 14:38	#4
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,534	Thanks. Now I see it, it probably only can happen if HAM uses overscan. HAM not being fully visible is handled correctly normally but in this case horizontal "blanking" is extended too far which breaks it. Not yet sure how to fix it.

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