Sprite Noob Question

[Anes]

Im rewriting my sprites engine since i was using the old "brad taylor" method as we know is outdated.
I find a problem when sprites have X=255 or 0xFF. When a sprite has this coordinate value is it visible?, since im getting errors.

Thanks in advance.

[lidnariq]

Sprite 0 hits don't trigger on sprites with X=255, even if there are visible pixels. Otherwise I think it's normal?

[Anes]

I know it doesn't trigger when its 255, but my question is if X is set intentionally at 255, is the the sprite pixel shown??

[Anes]

mean this:
I have 8 output units wich this unit is a C struct:

Code: Select all

typedef struct
{
	unsigned char Y, TileIndex, Attr, PT0, PT1, pre_spr_zero, spr_zero;
	int X;
} SPRBUFFER, * PSPRBUFFER;

"X" is copied from "sprite temp" memory in sprite fetches phase.

When rendering each ppu cc i decrese this "X", when X == 0 the unit is "active" and check if the sprite is not transparent.

What i got is this:

[mkwong98]

The game should not set 255 to the left sprite when Mario moves to the left edge of the screen so I think it is a bug with the CPU, not PPU.

[Sik]

Maybe it just assumes that Mario can never be off-screen horizontally? Especially since it'd be impossible to see on a TV anyway (due to overscan).

[Anes]

I solved it!! it was an sprite logic problem anyway I tested it in a real NES and it doesn't produce that effect.

[Zepper]

Now I'm curious.

Is this a bug? Isn't Mario sprite supposed to wrap?

[mkwong98]

Now I'm curious.

Is this a bug? Isn't Mario sprite supposed to wrap?

You are right, somehow that glitch didn't cross my mind when I saw the first picture.

[Zepper]

I solved it!! it was an sprite logic problem anyway I tested it in a real NES and it doesn't produce that effect.

What was your fix?? I'd like to know in details to fix my emu too.

[nostromo]

I've tested it in my Sony Triniton using service menu and it happends on real hardware(sorry by the image).

[tokumaru]

IIRC, SMB calculates sprite positions in a strange way, it doesn't surprise me that this bug is actually in the game.

[tepples]

Is this along the glitches that ShaneM fixed?

[Anes]

Yeah it happens in real hardware.

I have a real NES and a PAL Dendy. The thing that i couldn't test it in the real NES yestarday becouse my current transformer was broken and i tought that Dendy was the same, but not.

I have just bought one for the NES and IT DO HAPPEN.

[Zepper]

This sprite wrapping occurs in Nintendulator, but not on puNES. If Anes "has fixed it", it just took ppu_cycle MINUS sprite_xpos > 0 (should be >= 0).

So, that's it. No panic - it's not an emulator glitch.