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rm Vectors guide;

bjorn 5 years ago
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guides/Vectors.md

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-Vectors
-===
-
-This is a guide about the different built-in math objects: vectors, matrices, and quaternions.  All
-of these will be referred to as "vector objects" or just "vectors".  Vectors are useful because they
-can represent a multidimensional quantity (like a 3D position) using just a single value.
-
-```
--- Without vectors
-function object:update(dt)
-  object.x = object.x + object.vx * dt
-  object.y = object.y + object.vy * dt
-  object.z = object.z + object.vz * dt
-end
-
--- With vectors
-function object:update(dt)
-  object.position:add(object.velocity * dt)
-end
-```
-
-The following vector types are supported:
-
-- `vec2`
-- `vec3`
-- `vec4`
-- `quat`, a quaternion.
-- `mat4`, a 4D matrix.
-
-Most LÖVR functions that accept positions, orientations, transforms, velocities, etc. also accept
-vector objects, so they can be used interchangeably with numbers:
-
-```
-function lovr.draw()
-  -- position and size are vec3's, rotation is a quat
-  lovr.graphics.box('fill', position, size, rotation)
-end
-```
-
-Temporary vs. Permanent
----
-
-Vectors can be created in two different ways: **permanent** and **temporary**.
-
-**Permanent** vectors behave like normal LÖVR objects.  They are individual objects that are garbage
-collected when no longer needed.  They're created using the usual `lovr.math.new<Type>` syntax:
-
-```
-self.position = lovr.math.newVec3(x, y, z)
-```
-
-**Temporary** vectors are created from a shared pool of vector objects.  This makes them faster
-because they use temporary memory and do not need to be garbage collected.  To make a temporary
-vector, leave off the `new` prefix:
-
-```
-local position = lovr.math.vec3(x, y, z)
-```
-
-As a further shorthand, these vector constructors are placed on the global scope.  If you prefer to
-keep the global scope clean, this can be configured using the `t.math.globals` flag in `lovr.conf`.
-
-```
-local position = vec3(x1, y1, z1) + vec3(x2, y2, z2)
-```
-
-Temporary vectors, with all their speed, come with an important restriction: they can only be used
-during the frame in which they were created.  Saving them into variables and using them later on
-will throw an error:
-
-```
-local position = vec3(1, 2, 3)
-
-function lovr.update(dt)
-  -- Reusing a temporary vector across frames will error:
-  position:add(vec3(dt))
-end
-```
-
-It's possible to overflow the temporary vector pool.  If that happens, `lovr.math.drain` can be used
-to periodically drain the pool, invalidating any existing temporary vectors.
-
-Metamethods
----
-
-Vectors have metamethods, allowing them to be used using the normal math operators like `+`, `-`,
-`*`, `/`, etc.
-
-```
-print(vec3(2, 4, 6) * .5 + vec3(10, 20, 30))
-```
-
-These metamethods will create new temporary vectors.
-
-Components and Swizzles
----
-
-The raw components of a vector can be accessed like normal fields:
-
-```
-print(vec3(1, 2, 3).z) --> 3
-print(mat4()[16]) --> 1
-```
-
-Also, multiple fields can be accessed and combined into a new (temporary) vector, called swizzling:
-
-```
-local position = vec3(10, 5, 1)
-print(position.xy) --> vec2(10, 5)
-print(position.xyy) --> vec3(10, 5, 5)
-print(position.zyxz) --> vec4(1, 5, 10, 1)
-```
-
-The following fields are supported for vectors:
-
-- `x`, `y`, `z`, `w`
-- `r`, `g`, `b`, `a`
-- `s`, `t`, `p`, `q`
-
-Quaternions support `x`, `y`, `z`, and `w`.
-
-Matrices use numbers for accessing individual components in "column-major" order.
-
-All fields can also be assigned to.
-
-```
--- Swap the components of a 2D vector
-v.xy = v.yx
-```
-
-The `unpack` function can be used (on any vector type) to access all of the individual components of
-a vector object.  For quaternions you can choose whether you want to unpack the angle/axis
-representation or the raw quaternion components.  Similarly, matrices support raw unpacking as well
-as decomposition into translation/scale/rotation values.
-
-See `lovr.math` for the detailed API reference pages for the different vector types.