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POHow to do this coordinate system operation more efficiently?
 

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  1. POHow to do this coordinate system operation more efficiently?
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    <p>I'm making a 3D game, where the player's back should always be facing the camera and he should move in that direction. I didn't come to the "back facing the camera" part yet, but I believe that it will be simple once I figure out how to move the player in the right direction...</p> <p>Though it is a 3D coordinate system, height can be ignored (z-axis) because no matter how high the camera is, the player should always be going in the same speed (the camera system is planned to function much like in the game World of Warcraft).</p> <p>Now, I have summarized my problem to this...</p> <ul> <li>Point (0, 0) is the players position. </li> <li>Point (x, y) is the camera's position.</li> <li>The camera is (dx, dy) units away from the player (and because player is at (0, 0), it is also (x, y) units away, although this is a position vector, not a translation one)</li> </ul> <p>Problem: how do I get a point (a, b) in this 2D space that lies on a circle r = 1 but is on the same line as (0, 0) and (x, y)?</p> <p>Visualization:</p> <p><img src="https://i.stack.imgur.com/Ptqsj.png" alt="enter image description here"></p> <p>By doing this, I should have a 2D vector (a, b), which would, when multiplied by -30, act as the speed for the player.</p> <p>I know how to do this, but in a very expensive and inefficient way, using the Pythagora's theorem, square roots, and all those out-of-the-question tools (working in Javascript).</p> <p>Basically, something like this:</p> <pre><code>c = sqrt(dx*dx + dy*dy); //Get the length of the line rat = 1/c; //How many times is the desired length (1) bigger than the actual length a = x*rat; b = y*rat; </code></pre> <p>There must be something better!</p> <p>For reference, I'm making the game in Javascript, using the Three.js engine.</p>
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    1. UScorazza
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    1. COYes, that's pretty much what you have to do. How often do you need to calculate this? If it's only at the frame rate, it doesn't sound like a very big deal...
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      1. POHow to do this coordinate system operation more efficiently?
      1. USOliver Charlesworth
    2. COEvery time the mouse is moved, I guess. There's no other way? Bummer.
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    3. COThat's "expensive"? What kind of method are you hoping for?
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      1. POHow to do this coordinate system operation more efficiently?
      1. USWill Vousden
 

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