applyMatrix to mouseX and mouseY

When I use applyMatrix in a sketch to transform the coordinates, the mouseX and mouseY is not transformed accordingly.

The sketch explains the problem.

Is there any function that lets us apply the same matrix to mouseX and mouseY also?



It looks like you’re example is working fine. I think you might be misunderstanding how the applyMatrix() function works. In effect, you’re calling translate(width/2, height/2).

Once it’s called, any drawing functions, like ellipse(), or in your case, line(), has the matrix applied to it.

  // translating origin to the sketch center
  // This should actually draw a line from center to mouse, but it doesn't
  // as showed by the black line

line() only knows this: take 4 numbers, apply the matrix to them, draw the line. mouseX and mouseY are any other numbers.


After I applied the matrix. what I really needed to draw is -


This is something that I should automatically get. I should not be again trying to figure out how I can draw the line by comparing the changes that I made by applying the matrix.

So it should be like


mouseX and mouseY do not get effected by the matrix

With good reasons

Instead you have to add the values


Wouldn’t it be helpful if we have a function applyMatrixToMouse because I’m ready to implement that by contributing.

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You can search for the library Robot which has means to move the mouse cursor

Have you considered to write a small function which translates the canvas and the mouse coordinates? That way you only have to mention the translate values once:

let mX, mY;

function setup() {
  // code

function draw() {
  translateMore(width/2, height/2);  
  // code

function translateMore(_x, _y) {
  mX = mouseX - _x;
  mY = mouseY - _y;
  translate(_x, _y);

That seems to be a very good idea indeed. Probably I can also write functions like if I’m using scaling and rotation as well.

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Note that in WEBGL there isn’t actually a unique solution for this problem. That is because applyMatrix is 3D, and the mouse is 2D. So the question “after rotation, where can I draw a line such that it intersects ends visually intersecting with the mouse?” has a set of answers that form a ray cast from the mouse into 2D space. You would need to further constrain those answers based on something – the plane z=0, or perpendicular to point A with respect to the camera, etc. You can however ask the question the other way – for a given 3D point, what is the 2D screen position (screenX): see the library

There is a unique solution in 2D – it is just that this is a special case for matrices.

You may also be interested in this past issue, and the links in it:


what would be the answer for z=-200; ?

I struggle with that. It’s kind of inverse screenX