07876: genesis and clones: NTSC composite "rainbow effect" inaccuracies with HLSL (bgfx)

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
07876	Image Enhancement	Minor	Always	Feb 15, 2021, 23:02	May 1, 2023, 16:09

Tester	ICEknight	View Status	Public	Platform	MAME (Official Binary)
Assigned To		Resolution	Open	OS
Status [?]	Acknowledged			Driver	sega/mdconsole.cpp
Version	0.228	Fixed in Version		Build	64-bit
		Fixed in Git Commit		Github Pull Request #

Summary	07876: genesis and clones: NTSC composite "rainbow effect" inaccuracies with HLSL (bgfx)
Description	Trying to get HLSL's NTSC emulation to look like my Genesis Nomad and Japanese Mega Drive's composite output, I noticed that the "rainbow effect" looks more saturated than real hardware and its position seems to be a bit shifted (which might be related to https://mametesters.org/view.php?id=6892 ?). Best game for testing has to be Zero Tolerance, which shows some (accidental?) "holographic foil" effect on the title screen when using composite NTSC video (the effect isn't visible over RGB or on PAL systems).
Steps To Reproduce	-First load zerotol under the Genesis or Mega Drive system, using -video bgfx -Then, in order to get clean screenshots comparable to what you'd get on real hardware captures, configure HLSL like this: ----Effect: hlsl ----Shadow Mask: white ----Enable NTSC: On ----NTSC A Value: 0.00 ----NTSC B Value: 0.00 ----Scanline Duration (uSec): 47.7 ----Phosphor Persistence, Red: 0.00 ----Phosphor Persistence, Green: 0.00 ----Phosphor Persistence, Blue: 0.00 ----Scanline Amount: 0.00 -Then just wait for a bit for the title screen to show up.
Additional Information	I'm including direct video captures with both a generic Scart to HDMI adapter and an OSSC, for reference (all of them adjusted to a correct 4:3 aspect ratio): NTSC composite: NTSC RGB: PAL composite: PAL RGB:
Github Commit

Flags	Verified with Original
Regression Version
Affected Sets / Systems	genesis and clones

Attached Files	mame 47.7.png (323,829 bytes) Feb 15, 2021, 23:02 Uploaded by ICEknight MAME HLSL (scanline duration 47.7)
	crop composite generic.png (879,349 bytes) Feb 15, 2021, 23:05 Uploaded by ICEknight Genesis Nomad, composite, captured with generic Scart to HDMI (cropped)
	composite generic.png (993,588 bytes) Feb 15, 2021, 23:07 Uploaded by ICEknight Genesis Nomad, composite, captured with generic Scart to HDMI (full)

No.18834 ICEknight Tester May 11, 2021, 22:17 edited on: May 11, 2021, 22:50	Updated links to corrected footage and removed redundant video (sorry for any inconveniences due to the bump).