Hi together ! I am working on an adventure in the old Lucas-Arts-Style. To the question : What is the fastest way to determine the angle between a line (between 2 points) and the y-axis (meaning that 0° "is on top" of the y-axis)? In the moment I use vectors for that : Result := round(radtodeg(arccos((-Vector1.y)) / sqrt(sqr(Vector1.x)+sqr(Vector1.y))))); (thats Delphi-Code ...;-) I need the angle to determine the "facing" of the main character ! thx -crent-

Here's how I do it:

float
GetAngle(float x, float y)
{
float rslt;

1) handle special cases (0,PI/2,PI,3PI/2)
2) switch(quadrant)
2a) Q0: rslt = atanf(x/y);
2b) Q1: rslt = TWO_PI_F - atanf(-x/y);
2c) Q2: rslt = atanf(x/y) + PI_F;
2d) Q3: rslt = PI_F - atanf(-x/y);

return rslt; // (rslt in rads)
}

(I dunno Delphi but:
atanf is inverse tan (float version)
PI_F, TWO_PI_F are my float pi constants)

Also, this is assuming x,y are in rads already.

If anyone knows a faster way I'd surely like to hear about it!


-ns-


Edited by - NightShade on 1/10/00 3:16:40 PM

Edited by - NightShade on 1/11/00 8:54:51 AM