Compute shader output to vertex buffer

[SuperSimon81]

Hello and first of all let me just thank all of you for making this awesome library! Sorry for posting this in the wrong place before.

Now to my question. Is there a way to make a compute shader output to something like a vertex buffer for subsequent rendering? Is there some already available example perhaps, or would someone be willing to give me some pointers on how to achieve that?

Best regards.

[pezcode]

Basic idea would be:

• create vertex buffer with BGFX_BUFFER_COMPUTE_WRITE
• bind the buffer in your compute shader:
  • in C++: setBuffer(..., handle, bgfx::Access::Write)
  • in your shader:

    #include "bgfx_compute.sh"
    BUFFER_WR(vertexBuffer, vec4, ...);
    // ...
    vertexBuffer[0] = vec4(0.0);
    

• dispatch compute
• bind buffer with setVertexBuffer
• submit

You'll have to manually take care of the vertex stride since there's no way to bind the buffer with a struct type. If you need a different type than vec4, take a look at BGFX_BUFFER_COMPUTE_FORMAT_*** and BGFX_BUFFER_COMPUTE_TYPE_***

[SuperSimon81]

This worked thank you

[SuperSimon81]

I am now trying to make the buffer use a different type than vec4 since I´d like to store pos (x,y,z) and color (r,g,b). But cannot find any information on BGFX_BUFFER_COMPUTE_FORMAT_*** and BGFX_BUFFER_COMPUTE_TYPE_***. Is there any available documentation about this or some example I could look at?

[pezcode]

They're defined here:

bgfx/include/bgfx/defines.h

Line 280 in 534733f

#define BGFX_BUFFER_COMPUTE_FORMAT_8X1 UINT16_C(0x0001) //!< 1 8-bit value

There is no way to directly access vec3 so you're going to have to pad your vertex buffer layout to use vec4s, or use BGFX_BUFFER_COMPUTE_FORMAT_32X1 | BGFX_BUFFER_COMPUTE_TYPE_FLOAT with float in BUFFER_WR and write each vector component separately.

[SuperSimon81]

thank you again

[BluePrintRandom]

I have seen people use pixel in the past to get around apple not having openCL / correct support for some open subdivision the basic idea is each pixel is a location, and another buffer each is a euler or a quat , index in the buffer is vert index

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On Wed, Dec 16, 2020 at 8:09 AM pezcode ***@***.***> wrote: Basic idea would be: - create vertex buffer with BGFX_BUFFER_COMPUTE_WRITE - bind the buffer in your compute shader: - in C++: setBuffer(..., handle, bgfx::Access::Write) - in your shader: #include "bgfx_compute.sh" BUFFER_WR(vertexBuffer, vec4, ...); - dispatch compute - bind buffer with setVertexBuffer - submit You'll have to manually take care of the vertex stride since there's no way to bind the buffer with a struct type. If you need a different type than vec4, take a look at BGFX_BUFFER_COMPUTE_FORMAT_*** and BGFX_BUFFER_COMPUTE_TYPE_*** — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2333 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABW3SWPIIBQSXTNO6KOR2OLSVDLTVANCNFSM4U5VRJCA> .

[bkaradzic]

Is there some already available example perhaps, or would someone be willing to give me some pointers on how to achieve that?

24-nbody example generates positions for particles inside compute:
https://bkaradzic.github.io/bgfx/examples.html#nbody

[SuperSimon81]

thanks