08587: bgfx: Changing the BGFX chain at runtime in the slider menu turns off -prescale if it's on

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
08587	Image Enhancement	Minor	Always	Mar 22, 2023, 19:34	Mar 25, 2023, 22:32

Tester	ICEknight	View Status	Public	Platform	MAME (Official Binary)
Assigned To		Resolution	Open	OS	Windows 10/11 (64-bit)
Status [?]	Confirmed			Driver
Version	0.252	Fixed in Version		Build	64-bit
		Fixed in Git Commit		Github Pull Request #

Summary	08587: bgfx: Changing the BGFX chain at runtime in the slider menu turns off -prescale if it's on
Description	When using bgfx (any backend), setting a prescale value higher than 1 will make shaders like crt-geom look like the actual screen resolution is x times the real one (double amount of "scanlines", etc). Re-selecting the shader will discard the prescale and display the game's original resolution. No idea which of the two behaviors is the intended one.
Steps To Reproduce	-Set video to bgfx. -Set prescale to 2. -Set bgfx_screen_chains to lcd-grid, crt-geom, crt-geom-deluxe, etc. -Run any game with regular SD resolution (e.g.: "mame pbobble -prescale 2 -video bgfx -bgfx_screen_chains crt-geom"). The shader will treat the game's resolution as twice its size. -Open the slider controls, select another shader then reselect the previous one. Now the shader will treat the game's resolution as its regular size.
Additional Information
Github Commit

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Regression Version
Affected Sets / Systems

Attached Files	bgfx-crtgeom-prescale1.png (1,544,855 bytes) Mar 23, 2023, 16:13 Uploaded by ICEknight bgfx, crt-geom, prescale 1
	bgfx-crtgeom-prescale2.png (1,231,074 bytes) Mar 23, 2023, 16:14 Uploaded by ICEknight bgfx, crt-geom, prescale 2
	bgfx-crtgeom-prescale1-detail.png (13,796 bytes) Mar 23, 2023, 16:18 Uploaded by ICEknight bgfx, crt-geom, prescale 1
	bgfx-crtgeom-prescale2-detail.png (11,235 bytes) Mar 23, 2023, 16:18 Uploaded by ICEknight bgfx, crt-geom, prescale 2

No.21188 Robbbert Senior Tester Mar 23, 2023, 03:50	I'm not really sure what to look for here, but I couldn't seem to replicate your description. Using crt-geom, the frame rate drops to 69% and the sound is bad. The other choices all ran at 100%. My command line: >mame pbobble -prescale 2 -video bgfx -bgfx_screen_chains crt-geom The slider is called: Window 0, Screen 0 Effect crt-geom
No.21191 ICEknight Tester Mar 23, 2023, 16:19 edited on: Mar 23, 2023, 16:21	I've uploaded a couple of examples, only seems to happen with bgfx.
No.21193 Robbbert Senior Tester Mar 24, 2023, 00:11	Finally able to confirm it.
No.21211 john_iv Senior Tester Mar 25, 2023, 18:42	From RB in the Bannister shoutbox: R. Belmont: what actually happens: changing the BGFX chain at runtime in the slider menu turns off -prescale if it's on.
No.21212 ICEknight Tester Mar 25, 2023, 20:39	Ok, just updated the title and description.
No.21214 john_iv Senior Tester Mar 25, 2023, 22:32	Perhaps some related info (the overly large Fighters chain effect): https://github.com/mamedev/mame/issues/10859#issuecomment-1416892353 My pole position example from that comment produces the same effect in a clean x64 Windows build from tip of master this morning. mame.exe -version: 0.252 (mame0252-395-ge79f5257b01). Windowed or fullscreen. mame polepos -norc -bgfx_screen_chains hlsl -video bgfx -prescale 5 mame dkong -bgfx_screen_chains Fighters -norc -video bgfx -prescale 5