How to create a vertex buffer within different layout?

[TumblerSGQ]

When call setVertexBuffer , there'a _layoutHandle parameter. I think it's possible to user a vertexbuffer with different layout
But how to create a vertex buffer with different layout?

/// Set vertex buffer for draw primitive.
///
/// @param[in] _stream Vertex stream.
/// @param[in] _handle Vertex buffer.
/// @param[in] startVertex First vertex to render.
/// @param[in] numVertices Number of vertices to render.
**/// @param[in] _layoutHandle Vertex layout for aliasing vertex buffer. If invalid handle is
/// used, vertex layout used for creation of vertex buffer will be used.**
///
/// @attention C99 equivalent is bgfx_set_vertex_buffer.
///
void setVertexBuffer(
uint8_t _stream
, VertexBufferHandle _handle
, uint32_t _startVertex
, uint32_t _numVertices
, VertexLayoutHandle _layoutHandle = BGFX_INVALID_HANDLE
);

[pezcode]

Not entirely sure I understand your question, but I'll try:

You can create vertex buffers with createVertexBuffer, createDynamicVertexBuffer and allocTransientVertexBuffer(). All of them take a const VertexLayout& layout to use for creating them.

[TumblerSGQ]

I mean to create a VBO with different layout
eg:
pos/texcoord/pos/texcoord/...pos/normal/pos/normal

[TumblerSGQ]

I think a vbo is just a buffer object. How to use it is specified by glVertexAttribPointer and glDrawArrays(or glDrawElements)

[bkaradzic]

I mean to create a VBO with different layout
eg:
pos/texcoord/pos/texcoord/...pos/normal/pos/normal

Are you asking how to interleave pos/texcoord and pos/normal in array?!

[cloudwu]

I guess the question is how to create a vertex buffer with 2 or more layout.

I'm working on https://github.com/cloudwu/efkbgfx these days, and I found using a dynamic vertex buffer with 2 or more layout is impossible :( , because if I use bgfx_set_dynamic_index_buffer_with_layout to submit a part of dynamic vertex buffer with different layout , I can't calcuate the correct alignment.

[bikemurt]

I apologize if this is not what the original question was asking - but I am also curious as to the answer.

I'm wondering if vertex streams are possible for un-interleaved data. We all know that model importing, in most game engines, does a variety of things, but also re-packs the vertex data (position, normal, tangent, color, UVs, etc.) so they are interleaved and easily digestible by a single vertex buffer object.

In a GLTF exported from Blender, data for position will be packed as vector 3's (3 floats, 4 bytes per float), while the vertex color data will be packed as a vector4 (4 unsigned ints, 2 bytes per channel). While the color data is probably consuming about twice the space it needs to, I'm curious if this data could be unloaded from something like tiny-gltf directly into the GPU. In theory you might make a real-time model loader that bypasses the "model parsing" step, other than to actually load the GPU with vertex data and textures. The GLTF standard already provides the triangle indices so that part is trivial.

In OpenGL terms, each accessor and corresponding bufferView would get loaded as a VBO. Obviously I wouldn't want to do this if it produces multiple drawcalls, but I'm curious what bgfx could accomplish under the hood with multiple vertex streams.