# spherical and cylindrical billboarding

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Hi all,

I seem to get the theory behind this, first put 4 points at the same spot, map some coord, have the HLSL stretch those coord so that we make a quad, put texture in the middle.

For cylindrical:

Then on HLSL we calculate the position of the point, by taking the position and multiplying it by the world matrix only.. ? not sure here.

Then we create the lookat vector by taking the position - camera position.

We have our up vector which is like (0,1,0)

And I think we do a cross between the lookat vector and the up vector, so that we find the normal to both vector... this seems to be like a side looking kind of vector, and Normalize that side vector.

we then stretch the 4 points, into the final position.

-by adding a fix amount to the x cord and multiplying it by the side vector

-by adding a fix amount to the y cord and multiplying it by the up vector.

get view/projection matrix, and multiply the final position by the view projection matrix.

Finish it up by sending it the pixel shader and applying the texture.

Now, how do I do the same thing for the spherical billboard?

-tx

winsrp

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As you said, cross the lookat with 0,1,0 to get a side vector that will be used to move the points horizontally.

But for a spherical billboard to move the points vertically, instead of using 0,1,0, use the cross of lookat and side

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So I have to do it twice first the lookat vector with the up vector to find the side vector and then, the lookat again with the side vector right?

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it works!! now the only thing is that I'm putting the points for the billboards at 0,0,0, and I want to translate them to different positions each frame (making a little sun that moves around), but no matter what I put in the world matrix it always sets it in 0,0,0. Any ideas?

Edited by winsrp

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decided to ignore the world matrix, send in matrix identity and create the vertices every frame... besides, for the sun and the moon are just 12 vertices total, and I change the position of the vertices on the creation based on camera position, I just did a refinement since my sun image keep flipping when reaching high in sky, I just did a quick check with the upVector to keep it looking at the same place.

Thanks for the help.

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