Re: [stella] z26 (1.31)

[Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx>]

At 17:55 11.06.99 -0700, you wrote:

>Eckhard also wrote a pretty neat demo that helped to map out some of the
>weird properties that we implement.

In case anyone else wants to try this out, here is the demo. The
Stella programmers guide warns not to change the HMxx registers within
24 cycles after a HMOVE. This is what this demo does. It changes
HMxx, RESxx or HMCLR at various cycles after a HMOVE. Since this is
mostly relevant to games that do a HMOVE in every scanline to cover
up the HMOVE blanks, the demo does the HMOVE command at the beginning
of a scanline.

Moving the joystick left or right lets you change the value that gets
put into HMxx before the HMOVE. Moving the stick up or down lets you
change the value that gets put into HMxx after the HMOVE. It also lets
you select H for HMCLR and R for RESxx to be written to after the HMOVE.
Pushing the joystick button cycles through the different moving objects.
The top of the screen shows the prevalue, the postvalue and the object.
then there are 24 rows which show the object. The first row is the
object with no HMOVE motion. The others have hits to HMxx happen at
3 to 25 cycles after the HMOVE.

Since the ball graphics is always the same colour as the playfield,
I made it eight pixels wide, so that it can be seen more easiely.
The right difficulty switch lets you shift the background a bit,
which also hepls this.

The left difficulty switch changes into a special mode, where the
prevalue, the postvalue and the object are fixed and moving the
joystick left and right changes the cycle from $03 to $19. In this
mode only one of the rows of the other mode is shown, but this time
it's fullscreen. This help to identify the different Cosmic Ark stars
effects better. For example it shows, that the shift in CA is actually
17 pixels to the left and not 15 as I claimed before.

If you are to lazy to figure out the movement tables on your own,
you can have a look at John's source code for Z26 1.31.


Ciao, Eckhard Stolberg

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