C#•3y ago

Rotational matrix transformation

Yeh look i've got a point, and it's got an offset for both X, and Y. From These offsets we have a rotation(float) and we need to calculate the new center. My code is absolute garbage and i've got things close, but they're not close enough for pathfinder, and i'd like to actually understand whats going on a little bit more, if someone knows some more resources that relate to this? i've mainly arrived here by trial and error.(i know this is not c#) but this is more a conceptual question.

8 Replies

Doombox•3y ago

maths is not my strong suit so you'll have to bear with me a bit, but first you need to know the coordinates of the centre point and the point you want to rotate in the same co-ordinate system so you need those points to be both in world space or local space, whatever that means in your application

static (double newX, double newY) RotatePoint(
    double rotateX, double rotateY,
    double centerX, double centerY, 
    double angleInDegrees)
{
    var angleInRadians = angleInDegrees * (Math.PI / 180);
    var cosTheta = Math.Cos(angleInRadians);
    var sinTheta = Math.Sin(angleInRadians);
    return (cosTheta * (rotateX - centerX) - sinTheta * (rotateY - centerY) + centerX,
            sinTheta * (rotateX - centerX) + cosTheta * (rotateY - centerY) + centerX);
}

static (double newX, double newY) RotatePoint(
    double rotateX, double rotateY,
    double centerX, double centerY, 
    double angleInDegrees)
{
    var angleInRadians = angleInDegrees * (Math.PI / 180);
    var cosTheta = Math.Cos(angleInRadians);
    var sinTheta = Math.Sin(angleInRadians);
    return (cosTheta * (rotateX - centerX) - sinTheta * (rotateY - centerY) + centerX,
            sinTheta * (rotateX - centerX) + cosTheta * (rotateY - centerY) + centerX);
}

then you can use something like this

Doombox•3y ago

think my coordinates system might be messed up but it works

Doombox•3y ago

I hate maths, my head is already spinning

Xymanek•3y ago

by how many degrees trollnek

Doombox•3y ago

<a:gpa_pepe_spinhmm:985633122240573472> it never ends just spent the last few hours wrestling with github's garbage CI, then I decided to help someone with a maths question for no particularly good reason

TopendOP•3y ago

sorry it was 1am when i posted the question i will have feedback after work today!! cant be late for work -.-

TopendOP•3y ago

i love cat(mull-rom splines)•3y ago

you could also use Matrix4x4 with all its transformation functions to create a transformation matrix and multiply your vector with it it'll be a lot less work

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Rotational matrix transformation