Mesh-based cloth

Image1.jpg

main.lua

--- Test for cloth.

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-- a copy of this software and associated documentation files (the
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-- permit persons to whom the Software is furnished to do so, subject to
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--
-- The above copyright notice and this permission notice shall be
-- included in all copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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-- MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
-- IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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-- TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
-- SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
--
-- [ MIT license: http://www.opensource.org/licenses/mit-license.php ]

-- Standard library imports --
local ipairs = ipairs
local random = math.random

-- Modules --
local physics = require("physics")

-- Corona globals --
local display = display
local Runtime = Runtime
local timer = timer

-- Kick off physics.
physics.start()

-- Cell counts --
local NCols, NRows = 20, 30

-- Shorthand to hide point / cell confusion --
local VertsInRow = NCols + 1

-- Add indices in quads (straddling rows) and track edges containing them.
local edges, indices, ni = {}, {}, 0

for row = 1, NRows do
	local roff1 = (row - 1) * VertsInRow
	local roff2 = roff1 + VertsInRow

	for col = 1, NCols do
		-- Triangle 1
		indices[ni + 1] = roff1 + col -- will be ni - 5
		indices[ni + 2] = roff1 + col + 1 -- aka ni + 2, will be ni - 4
		indices[ni + 3] = roff2 + col -- aka ni + 3, will be ni - 3

		-- Triangle 2
		indices[ni + 4] = indices[ni + 2]
		indices[ni + 5] = indices[ni + 3]
		indices[ni + 6] = roff2 + col + 1 -- will be ni

		ni = ni + 6

		if row > 1 then
			-- Forward edge.
			edges[#edges + 1] = indices[ni - 5]
			edges[#edges + 1] = indices[ni - 4]
		end

		-- Downward edge.
		edges[#edges + 1] = indices[ni - 5]
		edges[#edges + 1] = indices[ni - 3]
	end

	-- Final downward edge.
	edges[#edges + 1] = indices[ni - 4]
	edges[#edges + 1] = indices[ni]
end

-- Last row: forward edges.
local roffn = ni - VertsInRow

for col = 1, NCols do
	edges[#edges + 1] = indices[roffn + col]
	edges[#edges + 1] = indices[roffn + col + 1]
end

-- Shorthand for content center --
local CX, CY = display.contentCenterX, display.contentCenterY

-- Mesh dimensions --
local W, H = math.floor(.6 * display.contentWidth), math.floor(.6 * display.contentHeight)

-- Hang the cloth from something.
local back = display.newRoundedRect(CX, CY - H / 2, W + 40, 50, 25)

back:setFillColor(.2, .3)
back:setStrokeColor(.1)

back.strokeWidth = 2

-- Add physics objects to an invisible group.
local ClothGroup = display.newGroup()

ClothGroup.isVisible = false

-- Cell dimensions --
local ColW, RowH = W / NCols, H / NRows

-- Upper-left corner of cloth --
local X0, Y0 = CX - W / 2, CY - H / 2

-- Calculate positions of cloth vertices / physics bodies.
local vertices = {}

for row = 0, NRows do
	local y, top = row * RowH, row == 0

	for col = 0, NCols do
		local x = col * ColW

		vertices[#vertices + 1] = x
		vertices[#vertices + 1] = y

		local body = display.newCircle(ClothGroup, X0 + x, Y0 + y, 5)

		physics.addBody(body, top and "static" or "dynamic")
	end
end

-- Add spring-like joints between all edges.
for i = 1, #edges, 2 do
	local b1, b2 = ClothGroup[edges[i]], ClothGroup[edges[i + 1]]
	local joint = physics.newJoint("distance", b1, b2, b1.x, b1.y, b2.x, b2.y)

	joint.dampingRatio, joint.frequency = .12 + random() * .14, random(15, 21) -- numbers from code.google.com/p/box2c
end

-- Show the cloth mesh.
local mesh = display.newMesh{ x = CX, y = CY, mode = "indexed", indices = indices, vertices = vertices }

mesh.fill = { filename = "Image1.jpg", type = "image" }

-- Update the vertices each frame to reflect the physics state.
Runtime:addEventListener("enterFrame", function()
	local mpath = mesh.path

	for i = 1, ClothGroup.numChildren do
		local body = ClothGroup[i]

		mpath:setVertex(i, body.x - X0, body.y - Y0)
	end
end)

do
	local Shuffle, N = {}, 0

	-- Populate an array (to be shuffled) with the indices of a few rows of points.
	local NWindRows = 10
	local From = math.floor(ClothGroup.numChildren / 2) - (NWindRows / 2) * VertsInRow
	local Total = NWindRows * VertsInRow

	assert(From >= Total, "Not enough rows to accommodate wind rows") -- catch easy-to-make tuning errors

	for col = 0, Total - 1 do
		Shuffle[#Shuffle + 1] = From - col
	end

	-- Every so often, randomly apply a force to a few points. To keep forces from
	-- accumulating, shuffle these around a bit.
	timer.performWithDelay(150, function()
		for _ = 1, 20 do
			-- Refill the array if empty. Otherwise, grab a random element and shrink it.
			if N == 0 then
				N = Total
			end

			local index = random(N)
			local pos = Shuffle[index]

			Shuffle[index], Shuffle[N], N = Shuffle[N], Shuffle[index], N - 1

			-- Apply some "wind" to one of the points.
			ClothGroup[pos]:applyForce(-.355 * random(), 0)
		end
	end, 0)
end

-- display.setDrawMode("wireframe")