Chapter 3: Against Intentions
These are the examples for chapter 3. Change to other chapters in the left menu.
The $64.000 Glitch
Page 3: In the December 1986 issue of Zzap!64 magazine, writer Julian Rignall explains his reaction to sideborder demos received from Dutch 1001 Crew:
"It was a portion of Bob Stevenson's Tutankhamen picture - which filled the whole screen! Somehow, the 1001 Crew have managed to dispose of the border - and as you hopefully can see from these screen shots the effect is quite stunning."
The Commodore Christmas Demo
Page 125: The 1982 Commodore Christmas Demo was distributed to Commodore dealers, demonstrating the music and colorful graphics of the machine. (Loading is authentically slow!)
The Aesthetics of 1989 C64 Demos
Page 137: Bones’ Larch 3 is oriented towards technical effects, with nearly every screen claiming technical novelty. The sideborder multiplexer is preceded by a screen explaining why the effect is technically impressive; the raster split and vertical sprite stretching routine; and real-time 3d with hidden lines.
Page 138: By comparison, Triangle’s Road of Excess (on which the author worked) has technical claims that are less explicit. Road of Excess is more designed, and more centered on cultural references – both in the title’s reference to William Blake’s poetry, and in callouts to bands. The second screen reuses the now well-known Tutankhamen image but remakes it in the FLI mode with additional colors and scrolling the image. The third screen first scrolls in the Triangle logo in perspective (and sideborder), then displays 3d objects. This demo also makes technical claims, but some of the screens establish cultural capital by referencing high culture or underground culture and exhibiting design skills such as graphic design.
Raster Beams and Raster Interrupts
Page 144: The TV’s raster beam draws the image line by line, from top to bottom. This small program waits for the raster beam to reach line 100, then sets the border color to red; it waits for line 200, then sets the color back to light blue. No characters, bitmaps, or sprites are changed, just the border color. (Source code.)
A program changing the border color using raster interrupts, changing the border 8 lines in a row for a raster bar effect. Note that the BASIC interface continues to function. (Source code.)
Showing more than 8 sprites (multiplexing)
Page 146: Simple multiplexing routine. Remember that the TV draws an image from top to bottom, and from left to right on each line. In this example, the program waits for line 10 at the top of the screen, then places the first 8 sprites in the top half of the screen. After these sprites have been displayed, the program moves the sprites to the bottom half of the screen, where they are displayed once the TV draws them there. At the top of the screen, we place the sprites in the top half of the screen again. This simple program shows 16 sprites in all. (Source code.)
Page 147-148: Sprite multiplexer program where the Commodore balloon is shown 32 times. The colored bars in the border show the time taken when new sprite positions are calculated (orange), the sprite list is sorted (red), the first sprites are positioned (black), and when sprites are moved for reuse (gray). Since the 6510 has no trigonometric functions, the circle movement is created using a precalculated table of sine and cosine values. In the 1980s, this table would be created with a BASIC program, but many present-day development tools have built-in facilities for making such tables. (Source code.)
Opening the borders
Page 148: Switching between 24 and 25-line mode at the right time - line 248 - tricks the VIC-II chip into forgetting to draw a border, allowing sprites to be shown. (Source code.)
Page 148: The sideborder trick is conceptually similar, but based on switching between 38 and 40 columns once every line, and requires more precise timing. (Source code.)
Later Demos and the Puzzling C64
Page 151: In this later demo, the 2008 Edge of Disgrace, where the C64 is used to produce graphically interesting visual effects with surprising colors, layouting the screen, and appearing more designed than the previous demos. Demos of this type rarely claim to represent novel hardware exploits, but they will present puzzles for the viewer, as much effort goes into breaking free from standard C64 dimensions (such as the size of a sprite) and layout (such as the border). They do often numerically improve on existing techniques or combine techniques such that it is non-obvious what is happening technically.
Page 152: The 2020 Memento Mori combines technically challenging effects such as sideborder scrolls and graphical rotation with references to art history. Its double-layered scrolling raises questions about what the layers are made of.
The 2023 Next Level demo combines several newer demo trends: Collaborations between groups previously competing, complicated programming that surprises without using new hardware tricks, nostalgia for early computing (here games), and assertions about the camaraderie of the demoscene.
Page 158: The Demoscene Starts Here. Magnification and analysis of the VIC- II chip,
pointing to the chip components that can be tricked into failing to activate the border