I'm not an expert but in the help file you can find
set object transparency :
0 - draw first no alpha
1 - draw first with alpha masking
2 and 3 - draw second which overlaps solid geometry
4 - draw second alpha test (only render beyond 0x000000CF alpha values)
5 - water line object (seperates depth sort automatically)
6 - combination of 3 and 4 (second phase render with alpha blend AND alpha test, used for fading LOD leaves)
For my trees i use the value of 6; it's the best choice in my opinion but with this option the pixel shader of your videocard make two passes !!!
I think that the DBP engine use something similar to the shader code below
+ Code Snippet pass RenderOpaquePixels
{
VertexShader = compile vs_2_0 VShader();
pixelShader = compile ps_2_0 PS();
AlphaBlendEnable = false;
AlphaFunc = Equal;
ZEnable = true;
ZWriteEnable = true;
CullMode = None;
}
pass RenderAlphaBlendedFringes
{
VertexShader = compile vs_2_0 VShader();
pixelShader = compile ps_2_0 PS();
AlphaBlendEnable = true;
SrcBlend = SrcAlpha;
DestBlend = InvSrcAlpha;
AlphaFunc = NotEqual;
ZEnable = true;
ZWriteEnable = false;
CullMode = None;
but i don't know exactly
Matteo