As a temporary replacent for the HDRP missing shader solution.
Note that there's SpeedTree v8 support included in HDRP 12 now.
Its adviced to use that shader instead if your project is on Unity v2021.2 .

Rationale behind this madness? -- I've needed a SpeedTree v6 shader for my trees to work with HDRP.

Done by using Amplify Shader Editor. If you don't have one - you probably won't be able to edit the shader.

Currently generated shader HDRP version is 10.5.0.
Other versions can be potentially supported by re-saving / regenerating shader via Amplify Shader Editor.

• SpeedTree v6; (Other versions of trees untested)
• HDRP 7.1.8 package ;
• Unity 2019.3.1.x ;
• For the wind to work - don't forget to add ShaderTimeControlExample.cs to the scene;
• (Optional) Amplify Shader Editor (for editing and tweaking the shader, and potential bugfixes. Also, its amazing)

(Other versions untested)

• Frag shader complete;
• Vertex shader complete;
• Most of the code is represented as ASE node graph / functions or custom expression injects.
• Time is controlled via ShaderTimeControlExample;
• Smoothness and Metallic can be tweaked via inspector;
• Hue variation does not work (yet).
• No mask maps. Can be added pretty easily, swap output for the tex sampler.

ASE should (in theory) simplify heavylifting done to port / change shader for other pipelines (e.g. URP)

Contains GBuffer as main pass. (Depth, Meta and forward as autogen via ASE)

This shader is ported from the fork I've made in ~2017 to modify and inject custom time. Also, any changes to the SpeedTree v6 original shader changes is probably missing from that past time to current.

(from C# script, checkout ShaderTimeControlExample)

Specify _GlobalTimerId to fetch according time from the array.

Or just override the FetchEternityTime function to the basic Time node and replace the output, that should feed default Unity's wind time. (if you feel risky)

It contains some parts of the code that doesn't translate to HDRP / ASE well.

Plus ASE doesn't have a built-in way to override _CullMode / _CullModeForward properties w/o overring templates atm.
If your culling is broken, reapply _Cull property, it should override hidden _CullMode / _CullModeForward

Don't expect everything to be 1:1 as in built-in SpeedTree v6 shader.

Also, use official shaders from SpeedTree once they're released. Or don't. Because you know. They don't support custom time :P

Q: Tried editing shader via ASE and Alpha Clipping stopped working (hall of mirrors issue)
A: ASE no longer sets _ALPHATEST_ON define, but rather relies on editor / inspector to set it as a local keyword. (This is by design, based on ASE support)
Inspector should now have a workaround that automatically adds keyword _ALPHATEST_ON to the material. Just by selecting materials it should be automatically added. 
After that you should be able to re-save shader. 

Alternatively, using debug mode in inspector and manually adding _ALPHATEST_ON keyword to the material should work.
Also, after messing around with alpha clipping make sure that output is connected correctly (Alpha Cutoff (_Cutoff) to Alpha Clip Threshold).

Q: Vertex Position is incorrect after editing (trees too large)
A: Vertex position should be Absolute. Set it manually to Relative, then back to Absolute and update the shader. This is ASE bug.

Q: "As Is" errors in older shader versions.
A: Safe to ignore, but if in doubt - I've updated shader recently, use that as a base.

Q: Why not Shader Graph?
A: Because it sucks (compared to ASE) right now

Q: Why not port manually via templates and shader code?
A: I've tried and failed miserably. As of current time, due to the lack of low-level shader documentation of the HDRP, this task seems more than impossible for a single person to accomplish over short period of time.

Feedback and bugfix requests please leave @ issues or here

Pine is made with SpeedTree Modeler (in ~2017 with v6).

SpeedTree and Unity license applies to the according parts / sources. ASE license applies for the ASE made shaders.