.PLS4 STA Q \ Set Q = A JSR ARCTAN \ Call ARCTAN to calculate: \ \ A = arctan(P / Q) \ arctan(P / A) \ \ The result in A will be in the range 0 to 128, which \ represents an angle of 0 to 180 degrees (or 0 to PI \ radians) LDX INWK+14 \ If nosev_z_hi is negative, skip the following BMI P%+4 \ instruction to leave the angle in A as a positive \ integer in the range 0 to 128 (so when we calculate \ CNT2 below, it will be in the right half of the \ anti-clockwise arc that we describe when drawing \ circles, i.e. from 6 o'clock, through 3 o'clock and \ on to 12 o'clock) EOR #%10000000 \ If we get here then nosev_z_hi is positive, so flip \ bit 7 of the angle in A, which is the same as adding \ 128 to give a result in the range 129 to 256 (i.e. 129 \ to 0), or 180 to 360 degrees (so when we calculate \ CNT2 below, it will be in the left half of the \ anti-clockwise arc that we describe when drawing \ circles, i.e. from 12 o'clock, through 9 o'clock and \ on to 6 o'clock) LSR A \ Set CNT2 = A / 4 LSR A STA CNT2 RTS \ Return from the subroutineName: PLS4 [Show more] Type: Subroutine Category: Drawing planets Summary: Calculate CNT2 = arctan(P / A) / 4Context: See this subroutine in context in the source code References: This subroutine is called as follows: * PL9 (Part 2 of 3) calls PLS4
Calculate the following: CNT2 = arctan(P / A) / 4 and do the following if nosev_z_hi >= 0: CNT2 = CNT2 + 32 which is the equivalent of adding 180 degrees to the result (or PI radians), as there are 64 segments in a full circle. This routine is called with the following arguments when calculating the equator and meridian for planets: * A = roofv_z_hi, P = -nosev_z_hi * A = sidev_z_hi, P = -nosev_z_hi So it calculates the angle between the planet's orientation vectors, in the z-axis.
Subroutine ARCTAN (category: Maths (Geometry))
Calculate A = arctan(P / Q)