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jotego / jtcores

FPGA cores compatible with multiple arcade game machines and KiCAD schematics of arcade games. Working on MiSTer FPGA/Analogue Pocket
https://patreon.com/jotego
GNU General Public License v3.0
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s18: sub pixel mixing #727

Closed jotego closed 3 months ago

jotego commented 4 months ago

There is a faint yellow line around the character portrait

image

Likely cause

This might be due to the vdp_sel being evaluated at the full clock rate. The vdp pixel is changing in between two pxl_cen pulses causing sub-pixel effects.

This should be visible in simulation waveforms, but maybe not in the simulation output image (as it is sampled at pxl_cen).

asturur commented 4 months ago

just a notice that the initial screen of moonwalker that is black and white is a great example of the issue ( clearly visible ) and is immediately after boot if that helps with simulation

jotego commented 4 months ago

just a notice that the initial screen of moonwalker that is black and white is a great example of the issue ( clearly visible ) and is immediately after boot if that helps with simulation

Very good advice. Thank you.

Zichio commented 4 months ago

I think these might be the same issue. I'm seeing blue outlines on both Moonwalker and Shadow Dancer ("Shadow Dancer (World).mra" and "Michael Jackson's Moonwalker (World) (FD1094-8751 317-0159).mra"). Looks like a blue outline to the left of the text. Been like this since the first release, was waiting to see if it would be fixed before reporting it.

These blue pixels are not present in MAME (tested newest version 0.267). I also did not spot the issue in some direct pcb footage i watched (but that was really low quality and hard to tell 100%).

Attatching two cropped screenshots (direct screenshot capture on MiSTer).

Moonwalker start-screen after adding a credit: Screenshot 2024-07-14 133904

Shadow Dancer, intro to the first level: Screenshot 2024-07-14 134021

Thanks for the excellent work as always JT and Team!

gyurco commented 3 months ago

Likely cause

This might be due to the vdp_sel being evaluated at the full clock rate. The vdp pixel is changing in between two pxl_cen pulses causing sub-pixel effects.

Just a note: on the schematics, while vdp_sel is combinatorial inside the PAL, the signals coming from the tilemap chip are delayed by 2 pixels (and registered with the pixel clock), due to they goes through 2 D flip-flops.

gyurco commented 3 months ago

The bug (and the fix) also affects Super Hang-On.

jotego commented 3 months ago

Fixed in 9807462 by @gyurco. @jtmiki mark it as completed.