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- Committer: Josh C
- Date: 2013-05-04 20:45:17 UTC
- Revision ID: josh@9ix.org-20130504204517-1rfp92svud12kg42
zoetrope 1.4
- files added:
- zoetrope
- zoetrope/core
- zoetrope/input
- zoetrope/sprites
- zoetrope/ui
- zoetrope/utils
added
removed
zoetrope/core/collision.lua
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-- Class: Collision
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-- This is a utility class that helps with collision detection. It's aware
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-- of <Sprite>s and <Group>s and makes sure collisions are resolved in the
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-- correct order (most overlap to least). You shouldn't have to use this class
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-- directly.
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--
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-- See Also:
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-- <Sprite.collide>, <Group.collide>
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Collision = Class:extend
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{
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-- Property: gridSize
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-- Default grid size used when checking collisions. Roughly speaking, this
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-- should be two times as big as your most common sprite size, but tweaking
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-- this number can yield better performance.
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gridSize = 25,
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-- Method: check
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-- Checks for collisions between <Sprite>s and <Group>s. If you call
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-- Collision:check(a, b, c), it will check for collisions between a and b,
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-- a and c, but not b and c.
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--
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-- It spatially hashes all objects into a grid, then checks for collisions via
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-- <Sprite.overlap()>. If an overlap is detected, then the collision is recorded.
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-- As a final step, this calls collidedWith() on sprites that collided, but in
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-- descending order of overlap. (This normally only triggers the onCollide() handler
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-- for the sprite, but <Map>s take advantage of this indirection.)
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-- The sequence of collision resolutions is important, so that displacement occurs
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-- in an order that prevents sprites from getting stuck on walls made of multiple sprites.
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--
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-- Arguments:
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-- a - primary <Sprite> or <Group>
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-- ... - any number of <Sprite>s or <Group>s to check for collisions against
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-- the A sprite or group
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--
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-- Returns:
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-- nothing
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check = function (self, a, ...)
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-- coerce all arguments into a flat list of sprites,
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-- recording where the first argument (or A group) sits in the list
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local args = {...}
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local list = self:solidSprites(a)
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local aLength = #list
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for _, item in pairs(args) do
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self:solidSprites(item, list)
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end
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-- build a spatial hash from the list, recording the grid
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-- cells that each of the sprites fits inside.
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-- we also record which cells each of the sprites in the A group
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-- sits in.
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local grid = {}
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local gridSize = a.gridSize or self.gridSize
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local gridded = {}
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local deferred = {}
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local aHuge = {}
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local aCells = {}
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for i, spr in ipairs(list) do
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if not gridded[spr] then
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local startX = math.floor(spr.x / gridSize)
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local endX = math.floor((spr.x + spr.width) / gridSize)
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local startY = math.floor(spr.y / gridSize)
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local endY = math.floor((spr.y + spr.height) / gridSize)
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-- Special casing of very large sprites (as defined as >= 25 cells in
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-- area). If they are in the A list, we just reserve them
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-- for later and check them against all sprites in the other lists.
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-- If they are not in the A list, we defer them to the very end of the gridding
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-- process, only to cells that have already been gridded by virtue of another
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-- sprite being in them.
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--
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-- The assumption here is that huge sprites are probably big tilemaps, and
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-- thus likely to collide with every sprite anyway.
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if (endX - startX) * (endY - startY) > 25 then
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if i <= aLength then
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table.insert(aHuge, spr)
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else
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table.insert(deferred, { spr = spr, startX = startX, endX = endX, startY = startY, endY = endY })
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end
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else
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if i <= aLength then
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aCells[spr] = {}
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end
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for x = startX, endX do
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grid[x] = grid[x] or {}
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for y = startY, endY do
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grid[x][y] = grid[x][y] or {}
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table.insert(grid[x][y], spr)
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if i <= aLength then
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table.insert(aCells[spr], grid[x][y])
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end
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end
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end
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end
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gridded[spr] = true
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end
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end
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-- Grid all huge sprites we just deferred. Unlike above,
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-- we only add them to grid cells that already have sprites in them.
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for _, d in pairs(deferred) do
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for x = d.startX, d.endX do
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if grid[x] then
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for y = d.startY, d.endY do
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if grid[x][y] then
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table.insert(grid[x][y], d.spr)
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end
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end
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end
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end
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end
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-- aCells now is a table whose keys are sprites in this group,
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-- and whose values are a table of grid cells that the sprite is in.
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-- We now build a list of collisions based on that.
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local collisions = {}
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local alreadyCollided = {}
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for aSpr, cells in pairs(aCells) do
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alreadyCollided[aSpr] = alreadyCollided[aSpr] or {}
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for _, cell in pairs(cells) do
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for _, bSpr in pairs(cell) do
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if aSpr ~= bSpr and not alreadyCollided[aSpr][bSpr] then
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local xOverlap, yOverlap = bSpr:overlap(aSpr.x, aSpr.y, aSpr.width, aSpr.height)
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if xOverlap ~= 0 or yOverlap ~= 0 then
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table.insert(collisions, { area = xOverlap * yOverlap, x = xOverlap, y = yOverlap, a = aSpr, b = bSpr })
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end
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-- record that we've already checked this collision
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alreadyCollided[bSpr] = alreadyCollided[bSpr] or {}
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alreadyCollided[aSpr][bSpr] = true
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alreadyCollided[bSpr][aSpr] = true
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end
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end
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end
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end
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-- Run through the huge sprites in the A list, if any, adding
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-- collisions to the existing list.
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for _, aSpr in pairs(aHuge) do
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alreadyCollided[aSpr] = alreadyCollided[aSpr] or {}
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for i = aLength + 1, #list do
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local bSpr = list[i]
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if aSpr ~= bSpr and not alreadyCollided[aSpr][bSpr] then
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local xOverlap, yOverlap = bSpr:overlap(aSpr.x, aSpr.y, aSpr.width, aSpr.height)
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if xOverlap ~= 0 or yOverlap ~= 0 then
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table.insert(collisions, { area = xOverlap * yOverlap, x = xOverlap, y = yOverlap, a = aSpr, b = bSpr })
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end
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alreadyCollided[bSpr] = alreadyCollided[bSpr] or {}
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alreadyCollided[aSpr][bSpr] = true
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alreadyCollided[bSpr][aSpr] = true
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end
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end
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end
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-- collisions now is a list, each item containing these properties:
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-- a - sprite colliding
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-- b - second sprite colliding
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-- x - x overlap
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-- y - y overlap
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-- area - square area of overlap
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--
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-- we now sort the table and resolve collisions in descending order of overlap area.
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table.sort(collisions, self.sortCollisions)
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for _, col in ipairs(collisions) do
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col.a:collidedWith(col.b, col.x, col.y)
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col.b:collidedWith(col.a, col.x, col.y)
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end
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end,
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-- Method: solidSprites
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-- Returns a table of <Sprite>s belonging to an object that
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-- should be collided with others, descending into groups.
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--
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-- Arguments:
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-- source - <Sprite> or <Group>
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-- existing - existing table to add to
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--
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-- Returns:
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-- table of <Sprite>s
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solidSprites = function (self, source, existing)
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local result = existing or {}
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if source.solid then
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if source.x and source.y and source.width and source.height then
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table.insert(result, source)
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elseif source.sprites then
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for _, spr in pairs(source.sprites) do
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if spr.sprites then
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result = self:solidSprites(spr, result)
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elseif spr.solid then
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table.insert(result, spr)
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end
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end
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end
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end
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return result
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end,
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-- Method: sortCollisions
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-- This sorts a table of collisions in descending order of overlap,
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-- suitable for use in conjunction with table.sort().
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--
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-- Arguments:
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-- a - one collision table
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-- b - one collision table
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--
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-- Returns:
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-- whether a should be sorted before b
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sortCollisions = function (a, b)
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return a.area > b.area
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end
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}
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