Creating a rotation vector for cpvrotate

[lucas]

Hi,
I'm trying to use the cpvrotate function to rotate an object I'm drawing. It's easy when I have a corresponding object, but this time I'm trying to do it with a radian value. Having a look at the rotation of some cpBodies, I got this:

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//rad is between -M_PI (-3.14...) and M_PI (3.14)
cpVect rot = cpv(1.0f, rad/M_PI);

This partially works, but it only rotates a quarter of the amount you'd expect and becomes smaller unless rot = cpv(1.0f, 1.0f).
How can I change the code to fix this?

Thanks!

[supertommy]

How about:

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cpVect rot = cpv(cosf(rad), sinf(rad));

[slembcke]

How about:

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cpVect rot = cpv(cosf(rad), sinf(rad));

Correct. The cpvrotate() function uses complex multiplication, so you just need a normalized vector. Also there is the function cpvforangle() that takes a radian value and gives you a normalized vector.

I am a bit confused why you are using cpvrotate() in order to rotate an object. What kind of object are we referring to exactly?

[lucas]

A polygon, but I haven't created it yet. When I use cpvrotate, it is being drawn using SDL when the mouse is held down.

Anyway, sinf and cosf work fine, thanks!

By the way, I dugg Chipmunk: http://digg.com/programming/Chipmunk_Ga ... ics_Engine