CODEWITHSUNDEEP
actionscript-3flashmathtrigonometry
Desmond Hume
Desmond Hume

Reputation: 8607

The atan2 function and axis directions

In this ActionScript reference on the atan2 function, it reads:

Computes and returns the angle of the point y/x in radians, when measured counterclockwise from a circle's x axis (where 0,0 represents the center of the circle). The return value is between positive pi and negative pi. Note that the first parameter to atan2 is always the y coordinate.

For example

Math.atan2(0.7071, -0.7071)

(note that the first parameter is the Y coordinate) returns 2.356, which is positive Pi*3/4.

But in Flash graphics the Y axis goes down, not up. Shouldn't it be "clockwise" instead?

Upvotes: 2

Views: 1572

Answers (1)

Lutz Lehmann
Lutz Lehmann

Reputation: 25972

This is the general description of what the atan2 function does in all programming languages.

With that said, you have to indeed put atan(-dy,dx) to get the counter-clock wise angle in screen coordinates, or atan2(dx,dy) to get the zero angle pointing upwards.

Upvotes: 6

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