[SOLVED] BillboardSet scale when setting setCommonDirection

[DanielSefton]

Hi,

For some reason the scale of a BillboardSet is determined by the length of the vector passed to setCommonDirection when the billboard type is BBT_PERPENDICULAR_COMMON.

The only mention in the docs of this behavior is in particle_width and particle_height:
http://www.ogre3d.org/docs/manual/manual_35.html

I've been looking at the source, and so far I saw that on line 588 it sets the bounding radius to the square length:

https://github.com/ehsan/ogre/blob/mast ... ardSet.cpp

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mBoundingRadius = Math::Sqrt(maxSqLen);

But I logged the bounding radius and this doesn't change. So now I have no idea what's causing it.

Basically I want to set the common direction of the billboard set without it affecting the scale at all.

Any help appreciated.

Daniel

[dark_sylinc]

Most likely this is caused by passing a non-unit-length vector? Try a normalizing the direction first.

[DanielSefton]

Sadly not, it occurs with unit-length vectors - when you pass UNIT_Y the scale of the billboard is zero, when you pass UNIT_Z the scale of the billboard is as it should be.

Basically the more direction it is towards UNIT_Y the smaller it gets.

I've solved it for now by just rotating the scene node 90 degrees, still find this issue strange though.

Thanks for the help

[Kojack]

Are you also setting the common up vector?
BBT_PERPENDICULAR_COMMON uses two vectors: common direction and common up vector. These two must be perpendicular to each other. The code for generating the billboard axes is:

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        case BBT_PERPENDICULAR_COMMON:
            // X-axis is up-vector cross common direction
            // Y-axis is common direction cross X-axis
            *pX = mCommonUpVector.crossProduct(mCommonDirection);
            *pY = mCommonDirection.crossProduct(*pX);
            break;

It appears pX and pY aren't normalised before use, and cross products of vectors are only unit length if they are perpendicular.
The default common up vector is unit y. If the common direction is also unit y then pX will be a vector of 0,0,0.

[DanielSefton]

Yeah that works I did try setting the common up vector before, but clearly I was setting the wrong directions. Thanks Kojack.