code: func (vs *VertexSlice) SetVertexData(data []float32) {
  	if len(data)/vs.Stride() != vs.Len() {
  		fmt.Println(len(data)/vs.Stride(), vs.Len())
  		panic("set vertex data: wrong length of vertices")
  	}
  	vs.va.setVertexData(vs.i, vs.j, data)
  }
docs: // SetVertexData sets the contents of the VertexSlice.
  //
  // The data is a slice of float32's, where each vertex attribute occupies a certain number of
  // elements. Namely, Float occupies 1, Vec2 occupies 2, Vec3 occupies 3 and Vec4 occupies 4. The
  // attribues in the data slice must be in the same order as in the vertex format of this Vertex
  // Slice.
  //
  // If the length of vertices does not match the length of the VertexSlice, this methdo panics.