96 pixels with 2 colors
The inspiration came from Chris' Star Castle logo. There's a couple minor differences due to the extra processing time that using DPC+ provides.
- The logo is centered instead of being slightly offset to the left.
- Instead of using VLBANK, I'm using SCORE mode to change the playfield pixels from green to black to hide the right and left edges of the screen
- I'm changing PF1 (in conjunction with SCORE) to hide an extra 8 pixels on the right that couldn't be masked with a missile.
Stella's debug colors:
The alternativing frames (phosphor mode off)
The blended image (phosphor mode on)
I could have changed the Playfield Color instead of using SCORE mode, but I'm planning to add the TV Type option from Timmy! so the color value to change the playfield back to green could not be hard coded. When writing the routine I didn't know I'd have X free for use, so thought I'd have to cache Green in ZP RAM which would required a 3 cycle read instead of 2. There's enough free time in the kernel that using ZP RAM would have been fine, but just like the free X register I didn't know that would be the case when I started coding the routine.
The TV-Type option will let me build a single ROM that works on NTSC, PAL and SECAM systems - though it has been reported that SECAM has a weird issue of sometimes turning red to grey.
When I came up with the 2-color 48 pixel routine for Stay Frosty 2 I also used VBLANK. It does have a minor issue, if the brightness of the display is too high the use of VBLANK is noticeable - I showed off that problem before when I finished the initial menu for Frantic.
http://www.atariage.com/forums/uploads//monthly_09_2011/blogentry-3056-0-09401600-1316196948.jpghttp://www.atariage.com/forums/uploads//monthly_09_2011/blogentry-3056-0-92516700-1316196960.jpg
With some inspiration from Omegamatrix, I was able to eliminate the use of VBLANK.
There is a minor issue with the technique - due to the way TIA generates the video signal there are vertical lines in the image.
I believe it's related to how the TIA generates its signal, which can cause other minor display issues like artifact colors.
If you're checking this out with Stella, be sure to turn on phosphor mode!
- open Draconian in Stella
- hit TAB for the in-game-menu
- select Game Properties
- Select the Display tab
- change Use Phosphor to Yes
- click OK
- select Exit Menu
- Reload the ROM (Control-R)
ROM
Source
Here's the stand alone program I worked up to figure out the timing.
Source and ROM for just the logo
Images without PF1 getting updated, alternating frames:
Blended:
actual:
ROM w/out PF1 changing
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