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I just started learning 2D game development using CreateJS and I was reading this article about angular velocity to learn how to correctly move a sprite in both x and y axis.

I understand most of it except the angle adjustment.

I learned that mostly, in games, (0,0) starts at the upper left part of the screen rather than the bottom left that we are familiar with in Math. I also learned that postive y means moving down rather than up.

Is the angle adjustment related to those? Why is the value -90 degrees?

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1 Answer 1

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As it says:

// Angle adjustment to make 0 up to match how our sprite was drawn.
var angleAdjustment = -90;

Likely that means the sprite was created with the plane facing right. This adjusts it to face "up". The angle doesn't have any thing to do with the coordinates system.

Remember that you can always use the coordinate system you're familiar with and convert to screen coordinates at render time (but that's a different question).

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  • \$\begingroup\$ I finally understood what you said. The angle adjustment is just a matter of the initial orientation of the image. You are correct, the plane is initally facing right. \$\endgroup\$ Commented Nov 22, 2013 at 6:12
  • \$\begingroup\$ Cool. You'll find other's code full of little hacks like that. Enjoy! \$\endgroup\$
    – House
    Commented Nov 22, 2013 at 7:10

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