func (q *commandQueue) appendVertices(vertices []float32) {
	if len(q.vertices) < q.nvertices+len(vertices) {
		n := q.nvertices + len(vertices) - len(q.vertices)
		q.vertices = append(q.vertices, make([]float32, n)...)
	}
	copy(q.vertices[q.nvertices:], vertices)
	q.nvertices += len(vertices)
}
func (q *commandQueue) appendVertices(vertices []float32) {
	if len(q.vertices) < q.nvertices+len(vertices) {
		n := q.nvertices + len(vertices) - len(q.vertices)
		q.vertices = append(q.vertices, make([]float32, n)...)
	}
	copy(q.vertices[q.nvertices:], vertices)
	q.nvertices += len(vertices)
}
// appendVertices appends vertices to the queue.