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251 lines
7.3 KiB
ReStructuredText
251 lines
7.3 KiB
ReStructuredText
Main Module
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===========
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::
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HC = require 'HC'
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The purpose of the main modules is to connect shapes with the spatial hash -- a
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data structure to quickly look up neighboring shapes -- and to provide
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utilities to tell which shapes intersect (collide) with each other.
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Most of the time, HC will be run as a singleton; you can, however, also create
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several instances, that each hold their own little worlds.
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Initialization
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--------------
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.. function:: HC.new([cell_size = 100])
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:param number cell_size: Resolution of the internal search structure (optional).
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:returns: Collider instance.
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Creates a new collider instance that holds a separate spatial hash.
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Collider instances carry the same methods as the main module.
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The only difference is that function calls must use the colon-syntax (see
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below).
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Useful if you want to maintain several collision layers or several separate
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game worlds.
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The ``cell_size`` somewhat governs the performance of :func:`HC.neighbors` and
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:func:`HC.collisions`. How this parameter affects the performance depends on
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how many shapes there are, how big these shapes are and (somewhat) how the
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shapes are distributed.
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A rule of thumb would be to set ``cell_size`` to be about four times the size
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of the average object.
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Or just leave it as is and worry about it only if you run into performance
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problems that can be traced back to the spatial hash.
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**Example**::
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collider = HC.new(150) -- create separate world
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-- method calls with colon syntax
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ball = collider:circle(100,100,20)
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rect = collider:rectangle(110,90,20,100)
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for shape, delta in pairs(collider:collisions(ball)) do
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shape:move(delta.x, delta.y)
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end
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.. function:: HC.resetHash([cell_size = 100])
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:param number cell_size: Resolution of the internal search structure (optional).
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Reset the internal search structure, the spatial hash.
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This clears *all* shapes that were registered beforehand, meaning that HC will
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not be able to find any collisions with those shapes anymore.
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**Example**::
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function new_stage()
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actors = {} -- clear the stage on our side
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HC.resetHash() -- as well as on HC's side
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end
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Shapes
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------
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See also the :doc:`Shapes` sub-module.
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.. note::
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HC will only keep `weak references
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<https://www.lua.org/manual/5.1/manual.html#2.10.2>`_ to the shapes you add
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to the world. This means that if you don't store the shapes elsewhere, the
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garbage collector will eventually come around and remove these shapes.See
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also `this issue <https://github.com/vrld/HC/issues/44>`_ on github.
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.. function:: HC.rectangle(x, y, w, h)
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:param numbers x,y: Upper left corner of the rectangle.
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:param numbers w,h: Width and height of the rectangle.
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:returns: The rectangle :class:`Shape` added to the scene.
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Add a rectangle shape to the scene.
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.. note::
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:class:`Shape` transformations, e.g. :func:`Shape.moveTo` and
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:func:`Shape.rotate` will be with respect to the *center, not* the upper left
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corner of the rectangle!
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**Example**::
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rect = HC.rectangle(100, 120, 200, 40)
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rect:rotate(23)
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.. function:: HC.polygon(x1,y1,...,xn,yn)
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:param numbers x1,y1,...,xn,yn: The corners of the polygon. At least three
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corners that do not lie on a straight line
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are required.
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:returns: The polygon :class:`Shape` added to the scene.
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Add a polygon to the scene. Any non-self-intersection polygon will work.
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The polygon will be closed; the first and the last point do not need to be the
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same.
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.. note::
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If three consecutive points lie on a line, the middle point will be discarded.
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This means you cannot construct polygon shapes that are lines.
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.. note::
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:class:`Shape` transformations, e.g. :func:`Shape.moveTo` and
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:func:`Shape.rotate` will be with respect to the center of the polygon.
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**Example**::
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shape = HC.polygon(10,10, 40,50, 70,10, 40,30)
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shape:move(42, 5)
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.. function:: HC.circle(cx, cy, radius)
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:param numbers cx,cy: Center of the circle.
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:param number radius: Radius of the circle.
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:returns: The circle :class:`Shape` added to the scene.
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Add a circle shape to the scene.
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**Example**::
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circle = HC.circle(400, 300, 100)
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.. function:: HC.point(x, y)
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:param numbers x, y: Position of the point.
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:returns: The point :class:`Shape` added to the scene.
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Add a point shape to the scene.
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Point shapes are most useful for bullets and such, because detecting collisions
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between a point and any other shape is a little faster than detecting collision
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between two non-point shapes. In case of a collision, the separating vector
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will not be valid.
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**Example**::
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bullets[#bulltes+1] = HC.point(player.pos.x, player.pos.y)
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.. function:: HC.register(shape)
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:param Shape shape: The :class:`Shape` to add to the spatial hash.
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Add a shape to the bookkeeping system.
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:func:`HC.neighbors` and :func:`Hc.collisions` works only with registered
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shapes.
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You don't need to (and should not) register any shapes created with the above
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functions.
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Overwrites :func:`Shape.move`, :func:`Shape.rotate`, and :func:`Shape.scale`
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with versions that update the :doc:`SpatialHash`.
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This function is mostly only useful if you provide a custom shape.
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See :ref:`custom-shapes`.
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.. function:: HC.remove(shape)
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:param Shape shape: The :class:`Shape` to remove from the spatial hash.
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Remove a shape to the bookkeeping system.
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.. warning::
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This will also invalidate the functions :func:`Shape.move`,
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:func:`Shape.rotate`, and :func:`Shape.scale`.
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Make sure you delete the shape from your own actor list(s).
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**Example**::
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for i = #bullets,1,-1 do
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if bullets[i]:collidesWith(player)
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player:takeDamage()
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HC.remove(bullets[i]) -- remove bullet from HC
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table.remove(bullets, i) -- remove bullet from own actor list
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end
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end
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Collision Detection
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-------------------
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.. function:: HC.collisions(shape)
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:param Shape shape: Query shape.
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:returns: Table of colliding shapes and separating vectors.
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Get shapes that are colliding with ``shape`` and the vector to separate the shapes.
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The separating vector points away from ``shape``.
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The table is a *set*, meaning that the shapes are stored in *keys* of the table.
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The *values* are the separating vector.
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You can iterate over the shapes using ``pairs`` (see example).
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**Example**::
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local collisions = HC.collisions(shape)
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for other, separating_vector in pairs(collisions) do
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shape:move(-separating_vector.x/2, -separating_vector.y/2)
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other:move( separating_vector.x/2, separating_vector.y/2)
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end
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.. function:: HC.neighbors(shape)
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:param Shape shape: Query shape.
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:returns: Table of neighboring shapes, where the keys of the table are the shape.
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Get other shapes in that are close to ``shape``.
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The table is a *set*, meaning that the shapes are stored in *keys* of the table.
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You can iterate over the shapes using ``pairs`` (see example).
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.. note::
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The result depends on the size and position of ``shape`` as well as the
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grid size of the spatial hash: :func:`HC.neighbors` returns the shapes that
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are in the same cell(s) as ``shape``.
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**Example**::
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local candidates = HC.neighbors(shape)
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for other in pairs(candidates) do
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local collides, dx, dy = shape:collidesWith(other)
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if collides then
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other:move(dx, dy)
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end
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end
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.. attribute:: HC.hash
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Reference to the :class:`SpatialHash` instance.
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