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Editorial Team
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Asked: 2026-06-16T23:39:17+00:00

In the accepted answer on this question: Java game – how to stop player

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In the accepted answer on this question: Java game – how to stop player from walking over obstacles I came across this code:

xSpeed = Math.cos(direction) * speed;
ySpeed = Math.sin(direction) * speed;

What does this do? I read (and guessed of course, because of the variable names) that it translates a direction and speed to an x speed and y speed. But what are sin and cos for? What kind of direction does this accept? Because AlekHalfHeart gave no further explanation I take it this is a quite common snippet, but I have never seen it before.

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1 Answer

  1. Editorial Team

    I think I figured it out thanks to Oli Charlesworth’s comment ‘If you draw a diagram of what is happening, you will get a triangle! ;)’ and a fair amount of diagrams. I’ll try to explain it, but I’ve never had math in English (I’m Dutch), so I don’t know the appropriate mathematical terms for everything, but I’ll try:

    I first didn’t understand where O. Charlesworth’s triangle was. But after a few drawings I figured out that the line of the movement the ‘player’ makes forms a triangle with the x axis or the y axis.
    After that I still didn’t understand what sine and cosine did there, but after rereading and generalising my math book I figured out that the the relation between the x-axis and the hypothenuse (the movement of the player – hey, I knew the English word for it!) equaled the distance along the x-axis traveled by the ‘player’. Fortunately (but not coincidentally, it’s MATHS), this is exactly what the cosine returns. If you replace x-axis with y-axis and cosine with sine, you got my explanation of why ySpeed = ... works.

    I fear my English explanation is not entirely correct, but that’s because of my English skills, not my maths skills. I hope it helps someone.

    PS I now realize my question was really vague. It’s a miracle it isn’t already closed.

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