At 15:22 29.05.99 -0700, you wrote:
>does this mean that i can position an object and perform a reset for the
>player/ball/
>missile and it will show up on the line FOLLOWING the scan line where
>the
>reset was performed (at the interval where it was reset)?
You have to position the object by hitting RESPxx and then you apply the
fine movement in the HMxx register by accessing HMOVE at the beginning
of the next scanline. When you store the value to the HMxx registers
doesn't matter much, because HMOVE will shift all five objects at
the same time according to the values in the five HMxx registers.
The thing about objects not showing up in scanlines where RESxx for that
object is accessed is a bit more complicated, but as long as you are
still learning the basics, it is OK to assume, that the object will
start displaying in the following scanline.
>2. if the HMOVE command has to be performed following a WSYNC, how does
>one place objects on the far left side of the screen and move them
>relative with the
>horizontal movement register if, to store a value in memory, takes 3
>cycles (9 pixels)? i would not need to actually write to the horizontal
>movement registers
>because i figure i can obtain the position and relative movement needed,
>during the
>housekeeping part of the program (which would be in non-picture
>lines)...
A scanline is 228 pixels wide, but only the last 160 pixels are
visible. So you have 68 pixels / 3 = 22 processor cycles to
prepare the values for positioning or to set up graphics for that
scanline etc.
BTW objects don't get positioned at the pixel that corresponds
with the processor cycle when the access to RESxx happens.
The missiles and the ball have a 4 pixel offset to the right,
normal players have a 5 pixel offset and double/quadruple
players seem to have a 6 pixel offset.
>3. this one doesnt really have to do with the horizontal movement...but
>if i write to the playfield registers during the actual scan line at
>different times for each register and leave playfield reflect off, is it
>possible to actually make a playfield thats longer
>than 20 bits?
Yes, that is possible. Many games that for example use the playfield
to display a title screen use this technique.
Ciao, Eckhard Stolberg
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