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Quick question about venetian blinds for 96-pixel displays

venetian venetian blinds 96 pixel kernel beginner

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#1 JeremiahK OFFLINE  

JeremiahK

    Space Invader

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Posted Thu Aug 10, 2017 3:03 PM

I'm sure this has been asked a dozen times before, but I tried searching the forums to no avail.

 

If you want to create a 96-pixel display (perhaps for a 12x 8-pixel-wide character display), you might set NUSIZ to 3-copies-medium for something like this:

 

P0 - P1 - P0 - P1 - P0 - P1 -     (the dashes represent 8-pixel-wide spaces)

 

Then, on the next scanline, you would shift P0 and P1 eight pixels to the right:

 

- P0 - P1 - P0 - P1 - P0 - P1

 

Then you would shift back to the left for the next scanline.  Classic venetian blinds effect.

 

So my question is this.  How do you deal with the problem of only being able to HMOVE 7 pixels to the left per scanline when you need 8 pixels?  Do you need to perform a shift on the graphics to fake it? (...if you have enough cycles, otherwise you would need a second graphics table that is already shifted).  That could work for a character display because there are spaces between letters.  But is there a better way to do this, especially if you need to use all 96 pixels without any blank spaces?  Do you need to strobe the RESPx registers in order to do this?  That's the only other way I can think of that might work, but I'm not sure, I haven't done any of that yet.

 

I don't have any example code yet.  I simply set up the players and NUSIZ, but that's it, no graphics or HMOVE's yet.  I'm just trying to figure out the best way to do it now rather than going down a few dead ends.



#2 RevEng ONLINE  

RevEng

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Posted Thu Aug 10, 2017 3:20 PM

Check out the HMOVE timing chart in the 2600 advanced programming guide. For the bB titlescreen 96-pixel minikernel, I used a cycle 74 hmove to go left 8 pixels.



#3 JeremiahK OFFLINE  

JeremiahK

    Space Invader

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Posted Thu Aug 10, 2017 7:22 PM

I will take a look at that, thank you so much for the fast reply.  I'm preparing for my first project which will be yet another 2048 game, hopefully with 24x24 pixel square tiles so the higher numbers will still look nice.







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