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So I am writing a game in C++, currently I am working on a 'Compass', but I am having some problems with the vector math..

Here is a little image I created to possibly help explain my question better enter image description here

Ok, so as you can see the 2D position of A begins at (4, 4), but then I want to move A along the 45 degree angle until the 2D position reaches (16, 16), so basically there is a 12 distance between where A starts and where it ends. And my qustion is how would I calculate this?

rflxdev
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    I remember seeing an earily similar question to this just the other day, but it doesn't make sense. Are you asking how to translate a point on a 2d plane, given a direction as an angle and a magnitude? – George May 02 '17 at 22:52
  • The question is very poorly defined, and as @George says simply doesn't make sense. Why do you want to move `A` using trig if you already know where it'll end up? Please clearly define the given information and consider moving the question to somewhere more appropriate such as the math stack exchange, as this has nothing to do with programming or c++. – Geoff May 02 '17 at 23:01

2 Answers2

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the simplest way in 2D is to take angle 'ang', and distance 'd', and your starting point 'x' and 'y':

x1 = x + cos(ang) * distance;
y1 = y + sin(ang) * distance;

In 2D the rotation for any object can be just stored as a single value, ang.

using cos for x and sin for y is the "standard" way that almost everyone does it. cos(ang) and sin(ang) trace a circle out as ang increases. ang = 0 points right along the x-axis here, and as angle increases it spins counter-clockwise (i.e at 90 degrees it's pointing straight up). If you swap the cos and sin terms for x and y, you get ang = 0 pointing up along the y axis and clockwise rotation with increasing ang (since it's a mirror image), which could in fact be more convenient for making game, since y-axis is often the "forward" direction and you might like that increasing ang spins to the right.

x1 = x + sin(ang) * distance;
y1 = y + cos(ang) * distance;

Later you can get into vectors and matricies that do the same thing but in a more flexible manner, but cos/sin are fine to get started with in a 2D game. In a 3D game, using cos and sin for rotations starts to break down in certain circumstances, and you start really benefiting from learning the matrix-based approaches.

Jason Lang
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  • Can you please look into it and answer me please https://stackoverflow.com/questions/68147891/c-graphics-how-to-move-an-object-with-specific-angle/ – Shivam Verma Jun 27 '21 at 07:59
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The distance between (4,4) and (16,16) isn't actually 12. Using pythagorean theorem, the distance is actually sqrt(12^2 + 12^2) which is 16.97. To get points along the line you want to use sine and cosine. E.g. If you want to calculate the point halfway along the line the x coordinate would be cos(45)(16.97/2) and the y would be sin(45)(16.97/2). This will work with other angles besides 45 degrees.

Francesco
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