VDELP0 Making P0 invisible?

[three2em]

Hey,

 

I'm working on a Kernel that needs to utilize VDELP for one of the players, but I'm running into this weird bug where if I have VDELP0 turned off, the sprite shows fine (albeit with some glitches because GRP0 is being changed mid-screen.) However, when I turn VDELP0 on, the sprite disappears. I can see GRP0 being written to properly in the Stella debugger, but that data never appears on screen. Any clue what's happening?

Edited October 2, 2015 by three2em

[three2em]

Whoops... Was just tinkering with the Kernel, and realized that because I'm only currently display P0 (haven't yet implemented P1 code), this was causing GRP0 not to be written. Weird.

[+SpiceWare]

Yep, you have to be updating both players for VDELPx to work.

 

Have you seen my blog series Collect? It teaches how to write a 2K Atari game from scratch, including how VDELPx works.

[three2em]

Darrell,

 

Thanks. Did not know about Collect, or maybe I did but don't recall the name. Will definitely be checking it out. Most of my kernel ideas I've been playing around with have been from reverse engineering Defender II's kernel, and unfortunately you can miss little bits of data like VDELP only works when both sprites are being updated. Anyway - Thanks for the link, checking it out now!