The Amiga Boing Ball Explained

We stayed in a mountain bungalow during summer vacation, there was a waterfall close enough to hear (and be loud) but far enough away that it's noise sounded like a pleasant version of TV static.

I had my best night's sleep in years. My theory was that it drowned out ambient bumps and crashes that usually wake me up at night.

It's worth mentioning the reveal, which the page omits entirely, and was the astonishing bit of the CES demo at the time.

In the original demo they were showing the normal desktop screen, showing window dragging, resizing, showing text editors, clocks, shell and what not. Running 640x480 4 colour. The whole time you could hear the bang bang of the boing ball bouncing, but see nothing.

At some point a viewer asks "what the heck's that noise?" and the demoer pulls down the desktop screen to smoothly, and without glitching, reveal a 320x240 32 colour screen running the Boing demo behind it. In its day, that was almost unbelievable. PCs had just got 16 colour EGA and switching res resulted in a couple of seconds of monitor blanking or losing sync as it switched.

I can't remember if they also had a 4096 colour HAM image (Hold and Modify - a way of cheating with palettes and getting a LOT more colours) behind that.

The Amiga had virtual screens that operated a little differently to a modern approach - they could be massive with a monitor sized viewport onto it. They could have multiple resolutions and bit depths. They could be brought forward and sent back, and dragged (only up and down) to reveal multiple screens at a time. Visualise having a full size browser window, and dragging the whole window down to reveal the desktop, but switching resolution and colours as you go.

People left speechless.

The copper (display co-processor) allowed switching of palette and resolution, with 0 cpu use, on a particular scan line every frame.

It seriously took 10 years or more before a Windows desktop could move stuff around the screen as smoothly, mainly as the Amiga didn't actually move a lot of stuff a PC did. PCs were upping colour depth as they aged rather than chasing more speed though. Virtual screens were a shadow of their Amiga implementation.

It might be obvious from the name, but there's also just one bit per pixel in a bitplane, and then you stack five bitplanes to get 32 colors.

You can have different offsets into each bitplane, which is why the grid could stay in the same place while the ball bounced.

The Amiga only supported bitplanes and not "chunky" modes like VGA where you have one byte per pixel. This made graphics with 256 colors (supported by the later AGA chipset) really slow as you had to do eight writes per pixel.

For a while there was a lot of competition between coders to write the best chunky to planar routine. This enabled you to write graphics effects with a chunky graphics buffer and then convert every frame on the fly to planar. One of the fastest was written by Kalms:

http://www.lysator.liu.se/~mikaelk/doc/c2ptut/

Water sounds are usually very relaxing.

The original demo had a bouncing effect.