I'm working on creating a lookup table I can use in the collision routine
for Death Derby where given the gremlin's X and Y, I figure out which RAM
strip to write to, which row of the RAM strip, and which bit to turn on.
Here is the preliminary in HTML with some assembly tables at the bottom:
http://www.homebrewgames.net/DeathDerby/index.cfm?action=playfield
Given this data structure what do you think the fastest lookup routing
would be?
I'm thinking the flow would be (in pcode):
copy Gremlin_X to a Gremlin_X_Temp
if (Gremlin_X_Temp > 79)
{
flag Temp_PF_Right for overwrite
Gremlin_X_Temp = Gremlin_X_Temp - 80 + 16
}
else
{
flag Temp_PF_Left for overwrite
}
loop through
Tombstone_Cell_Lookup_Table using index of "Cell"
if (current table number > Gremlin_X_Temp)
break out of loop
loop through
Row_Lookup_Table: using index of "Row"
find out which row we're on
if (current table number < Gremlin_Y)
break out of loop
use the Cell as in index into the
Temp_PF_Bit_Set_Table table and use that byte as a mask.
Set the bit of either the left or right RAM strip, indexed forward based on
the "Row"
This seems pretty straightforward, I hope.
But what I don't like is the two loops, which could result in a maximum of
11 iterations on rows and 8 iterations on cells.
Is there a faster approach?
If the row boundaries are every 16 scanlines and the tombstone cell
boundaries are every 8 pixels then I'm thinking some kind of left/right
shift approach could be used instead?
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