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The Story of Stay Frosty 2, Part 2


In 2009 a lot of work was taking place on the development of the Harmony/Melody Cart. October 17th saw this exchange in the Holiday Cart discussion area:

 

2009 Holiday Cart!

On 10/17/2009 at 1:32 AM, batari said:

<snip>

Now's the time to start talking about it.

On 10/17/2009 at 2:29 AM, Nathan Strum said:

Wouldn't August have been the time to start talking about it? icon_wink.gif

On 10/17/2009 at 11:06 AM, Albert said:

I have brought it up before, I think, but people were pretty distracted (rightfully so) with the Harmony cart. I'd be glad even to see a hack of an existing game at this point. icon_ponder.gif

 

..Al

On 10/17/2009 at 12:50 PM, SpiceWare said:

Yeah, I plan to get a Harmony and see what could be done for SF2 on Melody. I suspect it would be possible to use the full width of the playfield. Doing so would allow for multiple exits per screen that go to different screens.

 

Wonder if 3 fireballs per section would be Ok or generate too much flicker icon_ponder.gif

 

In spite of that, work was progressing on another holiday game - one that I hope will bear fruit (hehe) in the future.

 

 

In February 2010, while in Trinidad, I did some brainstorming:

On 2/22/2010 at 8:11 AM, SpiceWare said:

I'm down in Trinidad visiting my folks, but had some thoughts last night on SF2:

 

revised controls

  • left/right = move left/right
  • up = jump
  • down = stretch
  • fire = throw snowball

Stretch would be done by 2x and 4xing the player. The stretch would occur the direction you were facing and would be used to get to platforms you couldn't jump to (because of a platform over your head that prevents you from jumping). You're more vulnerable while stretched and would take twice the damage. If you've melted you can't stretch as far. Stretching would also cancel any momentum.

 

Throwing a snowball would shrink Frosty, just like running into a fireball does, so you have to make your shots count. Shrinkage may need to be a less than running into a fireball, that could be revised during play testing. <snip>

 

Revise the horizon routine to allow Frosty to be drawn over it so he doesn't "disappear" while jumping on the topmost platforms. This might preclude the night horizon though as the stars use NUSIZ and we'd end up with multiple Frostys in the horizon.

 

Level indicator - possibly flickered with lives remaining so there's no additional vertical space used up.

 

use DPC abilities of Harmony/Melody to draw players, missiles, ball. I'm not familiar with the capabilities, but will research more when I return home. I suspect tweeking the DPC support could provide interesting features, such as having a 16K game with the graphics data stored outside of the that 16K.

 

Things that would be nice to do with the time saved by using DPC:

  • full width playfield (this would also ease up timing by using a repeated instead of reflected playfield).
  • use ball as an elevator that is not fixed within a platform zone
  • carrot nose

 

The stretching idea came from Super Putty, a game I used to play on my Amiga 2000HD.

 

I bought my Harmony Cart in March, then began experimenting with DPC.

 

DPC only supports an 10K cartridge, consisting of two 4K banks and 2K of Graphics Data. Stay Frosty was a 12K game, so I asked if it'd be possible to make an "Expanded DPC "that supported seven 4K banks and 4K of Graphics data. Fred Quimby (batari), Chris Walton (cd-w) and I worked out the details and started to implement it. Because we also added new features, instead of just expanding the size, we changed the name to "Enhanced DPC". With Stephen Anthony(stephena)'s help, we updated Stella to support it. We also changed the name again, to DPC+, in order to fit Stella's one word only naming convention for the bankswitch formats. In April Stella 3.1 was released with preliminary support for DPC+. In May DPC+ was released. A week later the information for having DPC+ run ARM code was released, though at this time Stella did not support the execution of ARM code (that ability was added a year later in May 2011).

 

 

In September, thinking it'd be done in time for the 2010 holidays, I started over on Stay Frosty 2 using DPC+:

blogentry-3056-0-90397100-1418655742_thumb.png

 

A key feature was the snowman could appear in the horizon area:

blogentry-3056-0-35192000-1418655747_thumb.png

 

unlike in Stay Frosty, where he gets clipped:

blogentry-3056-0-30248400-1418655753_thumb.png

 

 

sf2_20100913.bin

 

Note: DPC+ saw numerous revisions during Stay Frosty 2's development so this ROM is not compatible with the latest version of Stella. The DPC+ driver is part of the ROM image, so this ROM will work on a Harmony Cartridge.

 

Blog entry covers 2009 thru September 13, 2010

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DPC

a co-processor chip created by David Patrick Crane. It speeds up things like the drawing of players, making it possible to draw a multicolored player(sprite) in 14 cycles instead of 26 (there's only 76 cycles per scanline, so freeing up 12 cycles allows you do additional updates on each scanline, resulting in a better looking game). Adds ability to use one of the Atari's voices to do in-game 3 voice music, leaving the other voice free for sound effects. It was used for Pitfall II. It can do a number of other things, like line drawing, which weren't used in Pitfall II. It would have been used for additional games, but the console market collapsed*. In Pitfall II the game uses bankswitching for 8K. It's probable that later DPC games could have used more ROM, we don't know. There's an additional 2K of graphic data that can't be directly accessed by the 6507, the DPC co-processor must be used to hand that data over to the 6507.

 

DPC+

An updated version of DPC. It speeds things up even more - that 14 cycle multi-color player(sprite) is now down to just 10 cycles. Takes away the "unused features" and replaces them with new ones, like the ability to manipulate the graphic data (in DPC the data is in ROM, in DPC+ it's in RAM). The bankswitching ability was expanded to 24K, the Graphics Data was expanded to 4K. The ARM chip emulates the DPC+ co-processor, just like it emulates the DPC coprocessor if you use a Harmony/Melody to play Pitfall II.

 

The ARM only needs to work as the co-processor when the visible portion of screen is being generated. So we added the ability to call ARM code during Vertical Blank and Overscan. You don't have to use it, but the ARM's a 70 MHz 32 bit CPU so it's able to do significantly more calculations than the Atari's 1 MHz 8 bit CPU.

 

*A big part of that was home computers had just become affordable in the USA - my friends and I all put away our consoles and were gaming on our new home computers.

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