Determining which face is "looking up"

[jmbrook2]

Hello,

I'm trying to work my way around the bullet library by making a sample application (bouncing dice). I've got them rendering and moving correctly (they look quite good) - however I'm a bit stuck on determining which face of the dice is facing up? (relative to the floor). Is there an easy way of querying the bullet 3d model to get this information?

Any pointers would be great,

Thanks in advance,

James

[sparkprime]

0x92c6008
0x92c6088
0x92c6108
0x92c6188

haha i'm so funny

What you can do though is push +Z (or whatever is 'up' in world space) through the inverse of the world transform of the die in question, to yield a vector in 'die space', which is something which you can then dot with all 6 possible face directions, picking the highest one.

[Flix]

Yep, I would do something similiar like this (never tested, so some adjustment should be done):

Code: Select all

btScalar maxValue = 0;
int maxIndex = -1;
for (int i = 0;i<6;i++) {
const int side = i >= 3 ? i-3 : i;
const bool negative = i>=3;
btScalar value = dice->getWorldTransform().getBasis().getColumn(side).dot(btVector3(0.,negative ? -1. : 1.,0.));//Actually I should negate the first term...
if (value>maxValue) {
 maxValue = value;
 maxIndex = i;
} 
}

Ok now we have maxIndex that is an unique number in the range [0,5] that should represent the result (if mapped correctly).

[jmbrook2]

Thanks Sparkprime & Flix,

I think I follow what is going on, I'll give it a go and see how I get on.

Just to add a bit more complexity I'm using jBullet and doing it on an Android device, but I'm sure it'll all work.

Thanks again,

James

[jmbrook2]

Hello Sparkprime & Flix,

Just to let you know this worked like a charm, I would have posted sooner but I forgot.

Thanks again,

James