class demosys.opengl.vao.VAO(name='', mode=4)

Represents a vertex array object. This is a wrapper class over moderngl.VertexArray to provide helper method.

The main purpose is to provide render methods taking a program as parameter. The class will auto detect the programs attributes and add padding when needed to match the vertex object. A new vertexbuffer object is created and stored internally for each unique shader program used.

A secondary purpose is to provide an alternate way to build vertexbuffers This can be practical when loading or creating various geometry.

There is no requirements to use this class, but most methods in the system creating vertexbuffers will return this type. You can obtain a single vertexbuffer instance by calling VAO.instance() method if you prefer to work directly on moderngl instances.


VAO.__init__(name='', mode=4)

Create and empty VAO

Keyword Arguments:
  • name (str) – The name for debug purposes
  • mode (int) – Default draw mode
VAO.buffer(buffer, buffer_format: str, attribute_names, per_instance=False)

Register a buffer/vbo for the VAO. This can be called multiple times. adding multiple buffers (interleaved or not)

  • buffer – The buffer data. Can be numpy.array, moderngl.Buffer or bytes.
  • buffer_format (str) – The format of the buffer. (eg. 3f 3f for interleaved positions and normals).
  • attribute_names – A list of attribute names this buffer should map to.
Keyword Arguments:

per_instance (bool) – Is this buffer per instance data for instanced rendering?


The moderngl.Buffer instance object. This is handy when providing bytes and numpy.array.

VAO.index_buffer(buffer, index_element_size=4)

Set the index buffer for this VAO

Parameters:buffermoderngl.Buffer, numpy.array or bytes
Keyword Arguments:
 index_element_size (int) – Byte size of each element. 1, 2 or 4

Render Methods

VAO.render(program: moderngl.program.Program, mode=None, vertices=-1, first=0, instances=1)

Render the VAO.


program – The moderngl.Program

Keyword Arguments:
  • mode – Override the draw mode (TRIANGLES etc)
  • vertices (int) – The number of vertices to transform
  • first (int) – The index of the first vertex to start with
  • instances (int) – The number of instances
VAO.render_indirect(program: moderngl.program.Program, buffer, mode=None, count=-1, *, first=0)

The render primitive (mode) must be the same as the input primitive of the GeometryShader. The draw commands are 5 integers: (count, instanceCount, firstIndex, baseVertex, baseInstance).

  • program – The moderngl.Program
  • buffer – The moderngl.Buffer containing indirect draw commands
Keyword Arguments:
  • mode (int) – By default TRIANGLES will be used.
  • count (int) – The number of draws.
  • first (int) – The index of the first indirect draw command.
VAO.transform(program: moderngl.program.Program, buffer: moderngl.buffer.Buffer, mode=None, vertices=-1, first=0, instances=1)

Transform vertices. Stores the output in a single buffer.

  • program – The moderngl.Program
  • buffer – The moderngl.buffer to store the output
Keyword Arguments:
  • mode – Draw mode (for example moderngl.POINTS)
  • vertices (int) – The number of vertices to transform
  • first (int) – The index of the first vertex to start with
  • instances (int) – The number of instances

Other Methods

VAO.instance(program:Program) → VertexArray

Obtain the moderngl.VertexArray instance for the program. The instance is only created once and cached internally.

Returns: moderngl.VertexArray instance


Destroy the vao object

Keyword Arguments:
 buffers (bool) – also release buffers