Docs: Basic pyrr stuff

Author: einarf

docs/source/pyrrmath.rst

@@ -2,7 +2,73 @@
 Matrix and Vector math with pyrr
 ================================
 
-This section needs more work. Probably the most relevant types
-to start with is Matrix*, matrix*, Vector and vector.
+Pyrr has both a procedural and object oriented api.
 
-See `pyrr <https://pyrr.readthedocs.io/en/latest/>`__ docs.
+See `pyrr <https://pyrr.readthedocs.io/en/latest/>`__ for official docs.
+
+.. Note:: We should probably add some more examples here. Feel free to
+   make an issue or pull request on github.
+
+Examples
+^^^^^^^^
+
+Identity
+
+.. code:: python
+
+    # procedural
+    >> m = matrix44.create_identity()
+    >> print(m)
+    array([[ 1.,  0.,  0.,  0.],
+           [ 0.,  1.,  0.,  0.],
+           [ 0.,  0.,  1.,  0.],
+           [ 0.,  0.,  0.,  1.]])
+
+    # object
+    >> m = Matrix44.identity()
+    >> print(m)
+    array([[ 1.,  0.,  0.,  0.],
+           [ 0.,  1.,  0.,  0.],
+           [ 0.,  0.,  1.,  0.],
+           [ 0.,  0.,  0.,  1.]])
+
+Matrices produced by ``Matrix44`` are also just numpy arrays as the class extends ``numpy.ndarray``.
+We can pretty much use the APIs interchangeably unless we rely on a method in the class.
+They can both be passed right into shaders as matrix uniforms.
+
+Rotation
+
+.. code:: python
+
+    # Short version
+    mat = Matrix44.from_eulers(Vector3(rotation))
+
+    # Long version
+    rot_x = matrix44.create_from_x_rotation(rotation[0])
+    rot_y = matrix44.create_from_y_rotation(rotation[1])
+    rot_z = matrix44.create_from_z_rotation(rotation[2])
+    mat = matrix44.multiply(x, y)
+    mat = matrix44.multiply(mat, z)
+
+Covert
+^^^^^^
+
+.. code:: python
+
+    # mat4 to mat3
+    mat3 = Matrix33.from_matrix44(mat)
+    # mat3 to mat4
+    mat4 = Matrix44.from_matrix33(mat)
+
+
+Common Mistakes
+^^^^^^^^^^^^^^^
+
+Matrices and vectors are just numpy arrays. When multiplying matrices,
+use the ``mult`` method/function.
+
+.. code:: python
+
+    mat = matrix44.mult(mat1, mat2)
+
+Using the ``*`` operator would just make a product of the two arrays.