crunch@well.UUCP (John Draper) (12/01/85)
HOW I THINK BOUNCING BALL WORKS - John Draper
I think there is an outer loop which scoots along getting addresses
of a round object (The ball). The ball appears to be the same size,
which must be a "Bob" type object. Probably the Anamation routines
were used. Each X, Y coord for the next incremental position would
only be stored in a table. The outer loop just increments a pointer
along the table (And no doubt arranged it "wrap around" fashion).
At the same time, the color registers were changed which gives the
ball a "Solid appearance" by drawing prescribe squares. Each of the
bitplanes were grouped as twos. Because the inside of the ball is in
two colors. This can give up to 8 positions the ball could be in
during one incremental phase.
The built in collision detection is used to trigger the "Boing" sound
when the ball collides with the bottom and the sides.
There are possibly two "Playfields" involved, because on the other
playfield, the "Shadow" could be drawn. When you put it all together,
the loop might look like this:
forever:
get next coords and data from table
"blit" the ball to the new position
and do the same for the shadow.
"toggle" the color registers to make it look like
the ball rotated, by selecting one of eight bitplanes
containing a "position" of the ball
handle collisions messages (if any).
loop back to "forever".
The kaleidescope program works in a similar fashion, except the
different mode where the image is "Stamped" or "Blitted" onto the
screen, then "Not erasing" itself. This must be some flag
set somewhere.
Now, to you Amiga Folks, this is the best guess I have as to how
it's done. I based this assumption when one of the Amiga folk said
that "sneaky tricks" were used to render the ball.
I spend a lot of time staring at the Amiga screen, wondering how
all that fast "Blitter" is done, along with collecting a large amount
of example source code. I am posting the majority of the code into
the Networks. BIX, WELL, Usenet, and Delphi. Sorry, Compuserve
but you are two expensive for me.
John Draper
The Crunch