Maths (Geometry): SNE

       Name: SNE                                                     [Show more]
       Type: Variable
   Category: Maths (Geometry)
    Summary: Sine/cosine table
  Deep dive: The sine, cosine and arctan tables
             Drawing circles
             Drawing ellipses
    Context: See this variable in context in the source code
 References: This variable is used as follows:
             * FMLTU2 uses SNE


 This lookup table contains sine values for the first half of a circle, from 0
 to 180 degrees (0 to PI radians). In terms of circle or ellipse line segments,
 there are 64 segments in a circle, so this contains sine values for segments
 0 to 31.

 In terms of segments, to calculate the sine of the angle at segment x, we look
 up the value in SNE + x, and to calculate the cosine of the angle we look up
 the value in SNE + ((x + 16) mod 32).

 In terms of radians, to calculate the following:

   sin(theta) * 256

 where theta is in radians, we look up the value in:

   SNE + (theta * 10)

 To calculate the following:

   cos(theta) * 256

 where theta is in radians, look up the value in:

   SNE + ((theta * 10) + 16) mod 32

 Theta must be between 0 and 3.1 radians, so theta * 10 is between 0 and 31.


.SNE

 FOR I%, 0, 31

  N = ABS(SIN((I% / 64) * 2 * PI))

  IF N >= 1
   B% = 255
  ELSE
   B% = INT(256 * N + 0.5)
  ENDIF

  EQUB B%

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