# p5.js | atan2() Function

• Last Updated : 21 Apr, 2020

The atan2() function in p5.js is used to calculate the angle from a specified point of origin measured from the positive x-axis. The values are returned in the range of PI to -PI as floating points. It is commonly used for orienting geometry to the position of the cursor.

Syntax:

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`atan2(y, x)`

Parameters: This function accepts two parameters as mentioned above and described below.

• y: It is a number that specifies the y-coordinate of the point.
• x: It is a number that specifies the x-coordinate of the point.

Return Value: It returns a number that denotes the arc tangent of the given point.

Below examples illustrate the atan2() function in p5.js:

Example 1:

 `function` `setup() {``  ``createCanvas(500, 200);``  ``textSize(18);`` ` `  ``text(``"Move the slider to observe the effects"``         ``+ ``" of the atan2() function"``, 20, 30);`` ` `  ``sliderXPos = createSlider(-200, 200, 0, 1);``  ``sliderXPos.position(20, 50);`` ` `  ``sliderYPos = createSlider(-200, 200, 0, 1);``  ``sliderYPos.position(20, 80);``}`` ` `function` `draw() {``  ``clear();``  ``text(``"Move the slider to observe the effects"``         ``+ ``" of the atan2() function"``, 20, 30);`` ` `  ``sliderXVal = sliderXPos.value();``  ``sliderYVal = sliderYPos.value();`` ` `  ``atan2Val = atan2(sliderXVal, sliderYVal);`` ` `  ``text(``"The X position value is: "` `+ sliderXVal, 20, 140);``  ``text(``"The Y position value is: "` `+ sliderYVal, 20, 160);``  ``text(``"The atan2 value is: "` `+ atan2Val, 20, 180);``}`

Output: Example 2:

 `function` `setup() {``  ``createCanvas(500, 400);``  ``textSize(18);``  ` `  ``text(``"Move the mouse to see the rectangle"``        ``+ ``" align to it."``, 20, 30);``}``  ` `function` `draw() {``  ``clear();``  ``text(``"Move the mouse to see the rectangle"``        ``+ ``" align with the mouse."``, 20, 30);``  ` `  ``// Move the rectangle to the``  ``// middle of the screen``  ``translate(width / 2, height / 2);``  ` `  ``// Use the atan2() function to find``  ``// the value according to the mouse``  ``// coordinates``  ``let adjustedValue = atan2(mouseY - height / 2,``                            ``mouseX - width / 2);``  ``rotate(adjustedValue);``  ` `  ``// Draw a rectangle``  ``rect(0, 0, 50, 25);``  ` `  ``text(adjustedValue.toFixed(4), 100, 20);``}`

Output: Online editor: https://editor.p5js.org/

Reference: https://p5js.org/reference/#/p5/atan2

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