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# Trouble with 2D speed vectoring.

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3 replies to this topic

### #1xzbobzx  Members

Posted 08 November 2012 - 11:20 AM

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?

### #2Álvaro  Members

Posted 08 November 2012 - 12:03 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().

### #3Cornstalks  Members

Posted 08 November 2012 - 12:07 PM

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

Aaaaaand ninja'd

Edited by Cornstalks, 08 November 2012 - 12:07 PM.

[ I was ninja'd 71 times before I stopped counting a long time ago ] [ f.k.a. MikeTacular ] [ My Blog ] [ SWFer: Gaplessly looped MP3s in your Flash games ]

### #4xzbobzx  Members

Posted 08 November 2012 - 01:14 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.

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.