Dragonfire is an arcade game by Imagic, a very popular game programming company that originally started with titles for the Atari 2600 console (and, in fact, was founded by ex-programmers from Atari itself). The game played in two stages: in the first stage one had to navigate between two turrets in a castle, jumping and ducking your way past fireballs and pits. Once you got through this stage, you entered the interior of the castle, where you had to collect treasures while dodging fireballs being hurtled at you by a large dragon.
Dragonfire was unique, and a technical marvel in Coco 1/2 gaming, due to the fact that it used sophisticated timing techniques to change video modes repeatedly during a scan refresh of the screen, in order to get a full 8 colors on the screen at once in the 128x192 graphics mode (which could normally only support 4 colors at a time). If you look closely at the intro and level 1 screenshots above, you will see that the top half of the screen has the left and right border areas using the pastel color set (white, cyan, magenta and orange, although not all of those colors were used), while the middle portion used the regular color set of green, yellow, blue and red). In fact, the size of the border areas where the color sets were changed actually changes itself, depending on how far down the screen refresh you were; you will notice the dark blue sky extends further at the very top, and it actually switches modes 5 times per scan line near the middle of the screen, where the center white/cyan bricks jut upwards into the other color set. Considering that the CPU ran at .895 MHz, and that the required timing to do such color set changes smoothly had to be done on a sub-scanline basis using the horizontal refresh (which occurs 15,750 times per second for a full scanline... and, remember, we are doing it up to 5 times DURING each scanline, or 5 times within 1/15,750th of a second), this was quite the programming feat. It is the ONLY game I know of that did this, and the only other programs I saw that used this technique was a demo by Steve Bjork in Color Computer Magazine, and Musica, which did split text/graphics screens... and even they only dealt with full scanlines, not sub-divided ones as done here. Very impressive programming.
It should noted: the color switching does NOT quite work correctly on a Coco 3, because of subtle timing changes on the GIME chip's emulation of the original 6847 VDG chip.
Author: Frank Ellis (artwork by Matthew Sarconi) (Imagic)
Publisher: Radio Shack/Tandy
Requires: Color Computer 1,2,3, 16K RAM, cartridge, joystick.
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