AngleFromSlope

AngleFromSlope Calculate angle given slope

#include <ToolUtils.h> Toolbox Utilities

short AngleFromSlope(theSlope );

Fixed theSlope ; ratio of dh/dv

returns angle in degrees (-180 to 180)

Given the slope of a line (the dh/dv or the horizontal change divided by the

vertical change between any two points on the line) AngleFromSlope

calculates the angle of that line. The calculation is approximate to the nearest

degree.

theSlope a 4-byte Fixed value; the dh/dv ratio of points on a line.

Returns: a signed short integer representing the angle most closely matching

the specified slope ratio. Positive values are clockwise from vertical

and negative values are counterclockwise.

Notes: The returned angle is expressed in circular degrees, going clockwise with

12 o'clock at 0°, 3 o'clock at 90°, etc. Negative values are

counterclockwise from straight up; e.g., 9 o'clock is -90°.

The following example calculates the slope of a line represented by two

endpoints and uses AngleFromSlope to derive the angle of the line.

Example

#include <ToolUtils.h>

#define INT2FIX(i) ((long) i << 16 )/* short to Fixed conversion macro */

Fixed theSlope;

Point startPt, endPt;

short theAngle, dh, dv;

dh = startPt.h - endPt.h; /* calculate the deltas */

dv = startPt.v - endPt.v;

theSlope = FixRatio( INT2FIX(dh), INT2FIX(dv) ); /* slope=dh/dv */

theAngle = AngleFromSlope( theSlope );

Referenced by (3):