Batches and groups

Without even needing to understand the details on how to draw primitives with the graphics API, developers can make use of Batch and Group objects to improve performance of sprite and text rendering.

The Sprite, Label and TextLayout classes all accept a batch and group parameter in their constructors. A batch manages a set of objects that will be drawn all at once, and a group describes the manner in which an object is drawn.

The following example creates a batch, adds two sprites to the batch, and then draws the entire batch:

batch = pyglet.graphics.Batch()
car = pyglet.sprite.Sprite(car_image, batch=batch)
boat = pyglet.sprite.Sprite(boat_image, batch=batch)

def on_draw()
    batch.draw()

Drawing a complete batch is much faster than drawing the items in the batch individually, especially when those items belong to a common group.

Groups describe the OpenGL state required for an item. This is for the most part managed by the sprite and text classes, however you can also use groups to ensure items are drawn in a particular order. For example, the following example adds a background sprite which is guaranteed to be drawn before the car and the boat:

batch = pyglet.graphics.Batch()
background = pyglet.graphics.OrderedGroup(0)
foreground = pyglet.graphics.OrderedGroup(1)

background = pyglet.sprite.Sprite(background_image,
                                  batch=batch, group=background)
car = pyglet.sprite.Sprite(car_image, batch=batch, group=foreground)
boat = pyglet.sprite.Sprite(boat_image, batch=batch, group=foreground)

def on_draw()
    batch.draw()

It's preferable to manage sprites and text objects within as few batches as possible. If the drawing of sprites or text objects need to be interleaved with other drawing that does not use the graphics API, multiple batches will be required.

Data item parameters

Many of the functions and methods in this module accept any number of data parameters as their final parameters. In the documentation these are notated as *data in the formal parameter list.

A data parameter describes a vertex attribute format and an optional sequence to initialise that attribute. Examples of common attribute formats are:

"v3f"

Vertex position, specified as three floats.

"c4B"

Vertex color, specified as four unsigned bytes.

"t2f"

Texture coordinate, specified as two floats.

See pyglet.graphics.vertexattribute for the complete syntax of the vertex format string.

When no initial data is to be given, the data item is just the format string. For example, the following creates a 2 element vertex list with position and color attributes:

vertex_list = pyglet.graphics.vertex_list(2, 'v2f', 'c4B')

When initial data is required, wrap the format string and the initial data in a tuple, for example:

vertex_list = pyglet.graphics.vertex_list(2,
                                          ('v2f', (0.0, 1.0, 1.0, 0.0)),
                                          ('c4B', (255, 255, 255, 255) * 2))

Drawing modes

Methods in this module that accept a mode parameter will accept any value in the OpenGL drawing mode enumeration; for example, GL_POINTS, GL_LINES, GL_TRIANGLES, etc.

Because of the way the graphics API renders multiple primitives with shared state, GL_POLYGON, GL_LINE_LOOP and GL_TRIANGLE_FAN cannot be used --- the results are undefined.

When using GL_LINE_STRIP, GL_TRIANGLE_STRIP or GL_QUAD_STRIP care must be taken to insert degenerate vertices at the beginning and end of each vertex list. For example, given the vertex list:

A, B, C, D

the correct vertex list to provide the vertex list is:

A, A, B, C, D, D

Alternatively, the NV_primitive_restart extension can be used if it is present. This also permits use of GL_POLYGON, GL_LINE_LOOP and GL_TRIANGLE_FAN. Unfortunately the extension is not provided by older video drivers, and requires indexed vertex lists.