Routines
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39081: Move a star depending upon the signs and magnitudes of its "direction"
Each time this routine runs, we add the smaller of the x- and y-magnitudes to the running "ratio" value in (IX+6).
If the larger of the x- and y-magnitudes is smaller than this, then we move the star in both x- and y-directions and subtract the larger magnitude from the running value in (IX+6).
If the larger of the x- and y-magnitudes is larger than this, then we move the star only in that direction with the larger magnitude and do not update (IX+6) further beyond adding the smaller magnitude (i.e. we do NOT subtract the larger one)
Used by the routine at 38884.
Input
IX Points to entry in star data table at 25614
Output
B New y-coordinate to plot
C New x-coordinate to plot
39081 LD A,(IX+6) Load current "ratio" value into A
39084 ADD A,(IX+8) Add smaller of x- and y-component magnitudes
39087 JR C,39094 If result is crosses the 255-0 boundary then skip ahead to 39094
39089 CP (IX+7) If result is less than larger of x- and y-component magnitudes...
39092 JR C,39105 ...then skip ahead to 39105 (move star only on axis with larger magnitude)
39094 SUB (IX+7) Subtract larger of x- and y-magnitudes
39097 LD H,(IX+5) Load y-step into H...
39100 LD L,(IX+4) ...and x-step into H (moving star on BOTH axes)
39103 JR 39111 Skip ahead to 39111
39105 LD H,(IX+3) Load 0 / y-step into H
39108 LD L,(IX+2) Load 0 / x-step into H
39111 LD (IX+6),A Update "ratio" value
39114 LD A,(IX+1) Add previous y-coordinate...
39117 ADD A,H ...to y-step...
39118 LD B,A ...in B
39119 LD A,(IX+0) Add previous x-coordinate...
39122 ADD A,L ...to x-step...
39123 LD C,A ...in C
39124 RET Return
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