Question about transparent object cast shadow.

An grass ( need alpha test ) using myself shader, it's shadow hasn't alpha test. ( left of the picture)
But The grass using the standard shader ( Rendering Mode: Transparent ), the shadow is correct, it's alpha test. ( right of the picture)
Why and how to make myself shader's shadow correct? thank you.

 

You need just need to add a fallback to a built-in transparent shader. If that doesn't work for some reason, you can add the parameter "addshadow".

 

I want to know how to can make the shadow like the right of picture. Because using myself shader, it isn't correct ( like the left of picture).