Trouble with 2D speed vectoring.

Math and Physics Programming

Started by xzbobzx November 08, 2012 05:20 PM

2 comments, last by xzbobzx 11 years, 5 months ago

120

Author

November 08, 2012 05:20 PM

So I'm working on a 2D, top-down racer-ish game and I devised an interesting algorithm using cosines and angles to calculate the speed vector. Too bad for me, it doesn't work like it's supposed to.



if( Rotation > 0 && Rotation < 90 )

{

  float Section_A = Speed*cos(90-Rotation);

  Velocity_Y = Speed*cos(Rotation);

  Velocity_X = Section_A - Section_A - Section_A;

}

else if( Rotation > 90 && Rotation < 180)

{

  float Section_B = Speed*cos(180-Rotation);

  float Section_C = Speed*cos(Rotation-90);

  Velocity_Y = Section_B - Section_B - Section_B;

  Velocity_X = Section_C - Section_C - Section_C;

}

else if( Rotation > 180 && Rotation < 270)

{

  float Section_D = Speed*cos(Rotation-180);

  Velocity_Y = Section_D - Section_D - Section_D;

  Velocity_X = Speed*cos(270-Rotation);

}

else if( Rotation > 270 && Rotation < 360)

{

  Velocity_Y = Speed*cos(360-Rotation);

  Velocity_X = Speed*cos(Rotation-270);

}

else if( Rotation < 1 )

{ Velocity_Y = Speed; Velocity_X = 0; }

else if( Rotation > 89 && Rotation < 91 )

{ Velocity_Y = 0; Velocity_X = Speed - Speed - Speed; }

else if( Rotation > 179 && Rotation < 181 )

{ Velocity_Y = Speed - Speed - Speed; Velocity_X = 0; }

else if( Rotation > 269 && Rotation < 271 )

{ Velocity_Y = 0; Velocity_X = Speed; }

Position_Y = Position_Y + Velocity_Y;

Position_X = Position_X + Velocity_X;

(0 rotation means the car is facing down, 90 it's facing left, 180 up, 270 right.
At >359 rotation goes insta 0.)

All that this does, is spaz out.
In my theory it should work, but apparently it does not.
Can anyone help?

alvaro

21,604

November 08, 2012 06:03 PM

I think this is all you need:

double const pi = atan(1.0)*4.0;

double const degrees = pi/180.0;



Velocity_X = -Speed * sin(Rotation * degrees);

Velocity_Y = Speed * cos(Rotation * degrees);

You need to make sure your angles are in radians before you pass them to cos() or sin().

Cornstalks

7,033

November 08, 2012 06:07 PM

Wild guess: most trig functions (sin, cos, etc.) work with radians, not degrees. Try converting your degrees to radians ([font=courier new,courier,monospace]radians = degrees * 3.14159265359f / 180.0f[/font]) before doing sin/cos.

[edit]

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xzbobzx

120

Author

November 08, 2012 07:14 PM

I think this is all you need:
double const pi = atan(1.0)*4.0; double const degrees = pi/180.0; Velocity_X = -Speed * sin(Rotation * degrees); Velocity_Y = Speed * cos(Rotation * degrees);

You need to make sure your angles are in radians before you pass them to cos() or sin().

That works great!
Thanks man, massive kudos.

Trouble with 2D speed vectoring.

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