Scratch

Project Notes

A ball bouncing in a room.

This new version should be easier to work out and also to make remixes from.

One loop does all the display, and another one does the position in 3D - bouncing, falling etc.

To remix, try duplicating the ball, and you'll get a second ball in no time. Change its starting coordinates and speed.

The old notes are here:

To understand this, download it first (!). The ball has 3 co-ordinates in the room: x, y, z positions (z is depth away from you). First, we decide on the proportions of the space where we are working. I wanted the ball to be half the size when it's at the far end, so z is transformed following this formula:

zfactor = 1+(z/400)

This way, if
- z=0, zfactor = 1 (max size)
- z=400, zfactor = 2 (furthest away, min size)

Now to place the ball we do:

screen x = x/zfactor
screen y = y/zfactor
size % = 100/zfactor

Simple, innit? It's called one-point perspective.

To get the ball to move, we use speed co-ordinates, like a ball in 2D, only there are 3 speeds, for the 3 axes. I added a co-ordinate to the "gravity ball" example provided with the samples.


Enjoy scratching