Basic question, a beginner !

[alvaro]

Hi,

can somebody tell me when this formula can be used, where can I get more information about it?

dir_x =  Math.cos(alpha*(Math.PI/180));
dir_y =  Math.sin(alpha*(Math.PI/180));
....

ball.pos_x+=dir_x ...
ball.pos_y+=dir_y ...

regards
Alvaro

[Orangy Tang]

Looks like an equation to generate a unit circle, what do you actually want it to do?

[Herkules]

You use it when calculating the x/y translation when you have a angle of direction given in degrees [0,360].

Did I get the question right?

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[Orangy Tang]

/me slaps forehead
Oh  yeah, convert an angle to a vector, that makes more sense. I had assumed that the alpha meant it was being interpolated over, instead its actually an input angle.

Guessing the question is still the tricky part though

[cfmdobbie]

Okay, while we're playing some kind of bizzare Jeopardy, try this:

Programmer Tom is writing some code and uses the decimal number 1597463007.  What is his method likely intended to do?

[kevglass]

Random number generator

Kev

[Jeff]

Thats fundemental trig.  Try any trigonometry textbook.

Alpha is your angle of direction in degrees.  pi/180 is a conversion from degress to radians, which is what all of the trig functions want.

sin == opposite/hypotenuse == Y part of that angle (assuming a total movement of 1,  hypotenuse is actually the total distance moved, opposite is the Y component.)  Note that this assumes a
trig style coordinate system where poitive Y is at the top and negative Y at the bottom.  if you are working in screen space you'll need to reverse it.

cos == adjacent/hypotenuse == X part of that component.

So your simple answer is. given a ship position x,y  and angle of motion alpha,  that math calculates the new position if the ship moves 1 unit in alpha direction.

Basic trig.  if you can't handle this you will have a LOT of "fun" trying to write game code....

[Jeff]

Btw...

This question has nothing to do with physcis and really belongs in "Newless Clubies" which is our total beginner topic.

[alvaro]

thank Jeff, you give me the answer I was looking for. Your answer about radians makes completly sence.

regards

[Jeff]

Glad I could help.

JK