Grass impostor billboards update


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Hello,

Updating from 2.6 way up to 2.11 we've encountered several issues with visuals based on grass_impostor_base.basemat:

1)

The most important one was that now billboards are half buried in the ground. By comparing the shaders I can see a difference in the way billboard vertices are positioned vertically, mainly this line (in core\shaders\grass\impostor\vertex\common.h):

vertex.xyz += binormal * ((in_data.texcoord.y - 0.5f) * height);

which, if converted to:

vertex.xyz += binormal * ((in_data.texcoord.y) * height);

produces the same results as 2.6, as this older version has it as:

vertex.xyz -= binormal * (IN_ATTRIBUTE(3).y * height);

Is this a breaking change? How to counter act this, by using the pivot_offset? But this is in world space?

 

2)

New material parameters were added at one point (2.7): phi and theta with default values 8 and 4. Previously you had impostor_transform (4 floats) with default values 8, 2, 0, 0). So second parameter didn't matched.

The update scripts didn't made the change (it just removed impostor_transform parameter without inserting phi and theta), had to manually track the error and update the materials.

 

Kind Regards,

Adrian L.

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Hi, ok thank you, will let our content devs use that tool and see if it fixes all issues.

I also noticed that after the world hierarchy xml content was updated, the prefab_id and linked_to_prefab_id attributes are no longer present (as they were present in 2.6 and 2.11 is no longer use those). Are these something I need to worry about?

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Not really. That was initial step that should ease migration to the new prefab system (which was later cancelled). So removing this will not break anything.

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