MEGA65: VIC-IV X Expanded sprites should display partially behind border.

[smnjameson]

From Discord:

TheNewGuy — Today at 4:44 PM
I'm currently converting a small C64 game to the MEGA65, using Xemu (merger branch) for testing. I've noticed the following issue:
On an actual C64 and in the VICE emulator, the right part of an x-expanded sprite will be visible near the left border if the x-coordinate is in range $e1 to $f7 and the MSB in $d010 is set.
In Xemu, the sprite is not visible at all, neither in C64 mode or for a 40 or 80 column screen in MEGA65 mode.
Does anybody know if this is just an issue/bug in Xemu, or if it happens on actual MEGA65 hardware as well?

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This is behaviour that existed on the C64 to allow the proper left hand border partial display of expanded sprites, and should be something that the Mega65 also allows. Note this also does not work on the real hardware so will be creating a duplicate issue there.

Test File (menu option A-E):
vic4tests.zip
Test shows no sprite at all.

MEGA65 issue on this: MEGA65/mega65-core#404

[lgblgblgb]

Just to be sure: unless MEGA65-core implements this, I won't do it for sure, otherwise it would be an emulation inaccuracy. In theory though it's not that hard to implement in Xemu as it sounds, just the sprite renders needs to allow to overflow the x_display_pos value, I would assume.