Using arrays

Using Arrays

PyGLM's array type was introduced in version 2.0.0 to reduce the likelihood of requiring users to also use numpy besides glm.

It's mainly intended to provide a way of passing multiple glm type instances (such as vectors) to external C functions
(such as glBufferData).

Table of contents

1. About arrays
2. Initialization
   • .. with vectors, matrices, quaternions or ctypes number objects
   • .. with other array instances
   • .. with other compatible arrays / lists / iterables
   • .. as a reference instead of a copy
   • .. with zeros
   • .. from numbers
3. Members
4. Methods
   • The copy protocol
   • Pickling
   • To list / tuple
   • From Numbers
   • As Reference
   • Zeros
   • Filter
   • Map
   • Sort
   • Concat
   • Repeat
5. Operators
   • Numeric operations
   • getitem and setitem
   • contains
   • len
   • str
   • repr
   • iter
   • hash

About arrays

PyGLM's arrays are pure data copies of one or multiple instances of a single PyGLM type.
For example, an array could copy the data of five different vec3 instances.
However, it cannot copy the data of instances, that don't have the same type, like two vec2 instances and one dvec2 instance.

Additionally, the data inside the array is only a copy, thus if the data inside the array is modified, it won't affect the instances it copied the data from.

Initialization

Arrays can be initialized in a few different ways.

... with vectors, matrices, quaternions or ctypes number objects

An array can be initialized with any number of vectors, metrices or quaternions, as long as they're all of the same type.

>>> array(vec3(1, 2, 3), vec3(4, 5, 6))
array(vec3(1, 2, 3), vec3(4, 5, 6))

>>> array(vec3(), ivec3())
TypeError: arrays have to be initialized with arguments of the same glm type

The same holds true for ctypes numbers:

>>> array(int8(2), int8(3))
array(c_int8(2), c_int8(3))

>>> array(int8(2), int16(3))
TypeError: arrays have to be initialized with arguments of the same type

You can also create an array of ctypes numbers from normal numbers using from_numbers, which needs to have the data type as it's first argument:

>>> array.from_numbers(int8, 2, 3)
array(c_int8(2), c_int8(3))

>>> array(int8, 2, 3) # alternative way
array(c_int8(2), c_int8(3))

Note: The list representations of vecs, mats and quats such as ((1, 2), (3, 4)) (an alias for mat2(1, 2, 3, 4)) cannot be used here.

... with other array instances

You can obtain a copy of an array by using the copy constructor.

arr_copy = array(arr)

... with other compatible arrays / lists / iterables

You can convert any compatible type to a PyGLM array.
This includes lists, tuples, etc. and types that support the buffer protocol (such as numpy's arrays):

>>> array((ivec1(), ivec1()))
array(ivec1(0), ivec1(0))

>>> array([dmat2()])
array(dmat2x2((1, 0), (0, 1)))

>>> array(numpy.array([[1,2,3]]))
array(ivec3(1, 2, 3))

>>> array([[1,2,3]])
TypeError: invalid argument type(s) for array()

Note: array buffers that store length 4 items are interpreted as vec4s rather than quats.

... as a reference instead of a copy

If you don't need or don't want a copy of an array or buffer, but want a reference instead (i.e. use the same data in memory as another array / buffer), you can do so by using glm.array.as_reference.

>>> arr = array(vec3(1))
>>> arr2 = array.as_reference(arr)
>>> arr == arr2
True

>>> arr.address == arr2.address
True

>>> arr[0] = vec3(2) # if you change one of them, the other changes as well
>>> arr2
array(vec3(2, 2, 2))

Note: as_reference only works with array instances or buffers (e.g. numpy.array).
Also it may not always be possible to create a reference copy, in which case a normal copy is made and a warning is raised.

... with zeros

You can initialize an array with any given number of zeros or a given type:

>>> array.zeros(4, uint8)
array(c_uint8(0), c_uint8(0), c_uint8(0), c_uint8(0))

>>> array.zeros(2, vec3)
array(vec3(0, 0, 0), vec3(0, 0, 0))

... from numbers

You can initialize an array with numbers and a (ctypes) data type using glm.array.from_numbers:

>>> array.from_numbers(int8, 1, 2, 3)
array(c_int8(1), c_int8(2), c_int8(3))

>>> array.from_numbers(float32, 4.2, 1.1)
array(c_float(4.2), c_float(1.1))

>>> array(int8, 1, 2, 3) # You can also use the array() constructor, but beware that the dedicated function is faster
array(c_int8(1), c_int8(2), c_int8(3))

>>> array.from_numbers(vec1, 1, 2, 3)
TypeError: Invalid argument type for from_number(), expected a ctypes data type as the first argument. Got 'type'

Members

PyGLM arrays have the following members:

Name	Type	Description
element_type	type	Type class of the contained elements (e.g. glm.vec3)
length	int	Number of elements contained by a given array
address	int	The memory address where an array's data is stored
ptr	c_void_p	A ctypes pointer that points to the content of an array
nbytes	int	The total data size in bytes
typecode	str	A single character, describing the data type of the elements' values, according to this list
dtype	str	A numpy-like data type string
ctype	str	The respective ctypes data type
itemsize	int	The size of one array element in bytes
dt_size	int	The size of each single component of the elements in bytes (size of data type)
readonly	int	Whether or not the array is read-only
reference	int	The reference to the array owning the data (if any)

Methods

The copy protocol

Arrays support the copy protocol (see here).  
You can use copy.copy(<array>) or copy.deepcopy(<array>) to get a copy of an array.

Pickling

Arrays support pickling (as of PyGLM 2.0.0), which is Python's serialization method.

To list / tuple

Any array has a to_list() and a to_tuple() function, which return's the arrays's data represented as a list or tuple respectively.

From Numbers

The array class has a static from_numbers method, which allows for creation of a one-dimensional array of numbers.
It takes a ctypes number type as it's first argument.
Example:

>>> array.from_numbers(c_float, 1.2, 3.4)
array(c_float(1.2), c_float(3.4))

>>> array.from_numbers(int32, 1, 3, 4, 5)
array(c_int32(1), c_int32(3), c_int32(4), c_int32(5))

As Reference

The array class also has a static as_reference method, which allows for creation of a reference copy of other arrays or objects that support the buffer protocol.

A reference copy means that the newly created array will use the same data in memory as the source array.
It will also keep a reference to the object it shares the data with in the reference member.
Example:

>>> arr = array(vec2(1))
>>> arr2 = array.as_reference(arr)
>>> arr == arr2
True

>>> arr is arr2.reference
True

>>> arr[0] = vec2(-1) # if you change one of them, the other changes as well
>>> arr2
array(vec2(-1, -1))

Zeros

Additionally, the array class has a static zeros method, which allows for creation of an array with items that are initialized with zeros.
This is the fastest way of creating an array, as it uses the builtin calloc function to allocate the memory and initialize it in the same step.

Example:

>>> array.zeros(4, uint8)
array(c_uint8(0), c_uint8(0), c_uint8(0), c_uint8(0))

>>> array.zeros(2, vec3)
array(vec3(0, 0, 0), vec3(0, 0, 0))

>>> array.zeros(1, mat4)
array(mat4x4((0, 0, 0, 0), (0, 0, 0, 0), (0, 0, 0, 0), (0, 0, 0, 0)))

Filter

You can filter an array using a custom filtering function (i.e. create a new array with all of this array's elements that match a certain criteria).

The filtering function is called with each element of the array and must return True for the elements to keep and False for the elements to discard.

Example:

>>> array(c_float, 1, 2, 3, 4, 5).filter(lambda x: x > 3)
array(c_float(4), c_float(5))

>>> array(vec3(1), vec3(2), vec3(3)).filter(lambda x: x.x + x.y == 2)
array(vec3(1, 1, 1))

Map

You can map the elements of an array to one or any number of new values using a custom mapping function.

The mapping function is supplied with the amounts of arguments that the map function is given.

If the mapping function returns None, the element is discarded (much like filter).
If it returns a single value, that value becomes a new element of the resulting array.
If it returns a tuple, all of the tuple's items are added to the resulting array.

When the mapping function returns numbers, they are interpreted as ctypes numbers of the same type as the array that map was called on.
If you want to specify a custom ctypes type to use, there is a keyword argument called ctype that can be used to do that.

Example:

>>> array(c_float, 1, 2, 3).map(lambda x: x + 1)
array(c_float(2), c_float(3), c_float(4))

>>> array(c_float, 1, 2, 3).map(vec3)
array(vec3(1, 1, 1), vec3(2, 2, 2), vec3(3, 3, 3))

>>> array(c_float, 1, 2, 3, 4, 5).map(lambda x: x if x > 3 else None)
array(c_float(4), c_float(5))

>>> array(c_float, 1, 2).map(lambda x: (x, x))
array(c_float(1), c_float(1), c_float(2), c_float(2))

>>> array(c_float, 1, 2).map(lambda x: (3, 4) if x == 1 else 5)
array(c_float(3), c_float(4), c_float(5))

>>> arr1 = array(c_float, 1, 2, 3)
>>> arr2 = array(c_float, 4, 5, 6)
>>> arr1.map(lambda x, y: (x + x) * y, arr2)
array(c_float(8), c_float(20), c_float(36))

>>> arr3 = array(c_float, 7, 8, 9)
>>> arr1.map(lambda x, y, z: vec3(x, y, z), arr2, arr3)
array(vec3(1, 4, 7), vec3(2, 5, 8), vec3(3, 6, 9))

>>> arr1.map(lambda x, y, z: x * y + z, arr2, arr3)
array(c_float(11), c_float(18), c_float(27))

>>> arr4 = array(vec3(1, 2, 3), vec3( 4, 5, 6))
>>> arr4.map(normalize)
array(vec3(0.267261, 0.534522, 0.801784), vec3(0.455842, 0.569803, 0.683764))

>>> arr5 = array(vec3(7, 8, 9), vec3(10,11,12))
>>> arr4.map(dot, arr5)
array(c_float(50), c_float(167))

>>> arr4.map(dot, arr5, ctype = c_int32)
array(c_int32(50), c_int32(167))

Sort

You can sort an array by using a custom sorting function.

The sorting function is called with two elements from the array and should return -1 if the first element comes before the second element in order.
Otherwise it may return any other value. Typically 0 for equal elements and 1 if the first element comes after the second.

The sorting algorithm used is a recursive quicksort.

Example:

>>> arr = array(c_float, 6, 5, 4, 3, 2, 1)
>>> arr.sort(lambda x, y: -1 if x < y else 1)
>>> arr
array(c_float(1), c_float(2), c_float(3), c_float(4), c_float(5), c_float(6))

>>> arr.sort(lambda x, y: int(sign(y - x)))
>>> arr
array(c_float(6), c_float(5), c_float(4), c_float(3), c_float(2), c_float(1))

>>> arr.sort(cmp) # using glm.cmp
>>> arr
array(c_float(1), c_float(2), c_float(3), c_float(4), c_float(5), c_float(6))

Concat

Arrays can be combined / concatenated using the concat() method, as long as they have the same element type.

>>> array(vec2(1, 2)).concat(array(vec2(3, 4)))
array(vec2(1, 2), vec2(3, 4))

>>> array(vec4()).concat(array(vec1()))
ValueError: the given arrays are incompatible

Repeat

Arrays can be repeated a given number of times using the repeat() method.

>>> array(vec3(1, 2, 3)).repeat(3)
array(vec3(1, 2, 3), vec3(1, 2, 3), vec3(1, 2, 3))

Operators

Numeric operations

Arrays support a dozen numeric operations:

• Addition (+)
• Subtraction (-)
• Multiplication (*)
• Division (/)
• Modulus (%)
• Power (**)
• Negation (-)
• Absolution (abs())
• Inversion (~)
• Left shift (<<)
• Right shift (>>)
• Bitwise and (&)
• Bitwise or (|)
• Bitwise xor (^)

Note: Not all types are compatible though.

getitem, setitem and delitem ([] operator)

You can access the individual elements of an array using indices.
Likewise you can also modify it's data by overwriting it or delete it using del

>>> arr = array(vec1(1), vec1(2), vec1(3))
>>> arr[0]
vec1( 1 )

>>> arr[1] = vec1(0)
>>> arr
array(vec1(1), vec1(0), vec1(3))

>>> del arr[2]
>>> arr
array(vec1(1), vec1(0))

You can also use slices to get or modify sub-arrays:

>>> arr = array(vec1(1), vec1(2), vec1(3), vec1(4))
>>> arr[:2]
array(vec1(1), vec1(2))

>>> arr[::2]
array(vec1(1), vec1(3))

>>> del arr[1:3]
>>> arr
array(vec1(1), vec1(4))

>>> arr[:] = array(vec1(8), vec1(9))
>>> arr
array(vec1(8), vec1(9))

Slices have the following syntax: start_index : stop_index : optional_step, meaning you start at start and go step steps until you've reached or passed stop (exclusive) or the greatest possible index.

contains (in operator)

You can check wether or not an element is present in the array using the in operator.

>>> arr = array(vec2(1, 2), vec2(3, 4))
>>> vec2() in arr
False

>>> vec2(3, 4) in arr
True

>>> vec2(2, 3) in arr
False

len

You can acquire the length of an array using the built-in len() function.

>>> len(array(vec1(0), vec1(1)))
2

>>> len(array(vec2(0, 1), vec2(2, 3), vec2(4, 5)))
3

str

You can get a string representation of an array using the built-in str() function.
Example:

>>> print(str(array(vec2(1, 2), vec2(3, 4), vec2(5, 6))))
[
 [            1,            2 ],
 [            3,            4 ],
 [            5,            6 ],
]

>>> print(str(array(mat2(1, 2, 3, 4), mat2(5, 6, 7, 8))))
[
 [
  [            1,            2 ],
  [            3,            4 ],
 ],
 [
  [            5,            6 ],
  [            7,            8 ],
 ],
]

repr

You can get a reproducable string representation of an array using the built-in str() function.
Example:

>>> print(repr(array(vec2(1, 2), vec2(3, 4), vec2(5, 6))))
array(vec2(1, 2), vec2(3, 4), vec2(5, 6))

>>> print(repr(array(mat2(1, 2, 3, 4), mat2(5, 6, 7, 8))))
array(mat2x2((1, 2), (3, 4)), mat2x2((5, 6), (7, 8)))

iter

You can get an iterator from an array using iter()

>>> arr = array(vec2(1, 2), vec2(3, 4))
>>> it = iter(arr)
>>> next(it)
vec2( 1, 2 )

>>> next(it)
vec2( 3, 4 )

hash

You can generate a hash value for arrays using hash()
Example:

>>> arr = array(vec3(1), vec3(2), vec3(3), vec3(4))
>>> hash(arr)
-2624592468369027458
>>> arr2 = array(vec3(1), vec3(2), vec3(3))
>>> hash(arr2)
9163283608357050393
>>> arr3 = arr2 + array(vec3(4))
>>> hash(arr3)
-2624592468369027458