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2bt/main.lua

Last active February 17, 2016 01:47
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Revisions

  1. 2bt revised this gist Feb 17, 2016. 1 changed file with 2 additions and 3 deletions.
    5 changes: 2 additions & 3 deletions main.lua
    View file
    Original file line number Diff line number Diff line change
    @@ -1,6 +1,5 @@
    local G = love.graphics


    function splitPoly(poly, mx, my, dx, dy)
    local poly_a = {}
    local poly_b = {}
    @@ -47,8 +46,8 @@ function splitPoly(poly, mx, my, dx, dy)
    end


    -- input: two concave polygons
    -- output: list of concave making up the difference
    -- input: two convex polygons
    -- output: list of convex polygons making up the difference
    function subtractPoly(minuend, subtrahend)
    local result = {}
    local bar = minuend
  2. 2bt created this gist Feb 17, 2016.
    106 changes: 106 additions & 0 deletions main.lua
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,106 @@
    local G = love.graphics


    function splitPoly(poly, mx, my, dx, dy)
    local poly_a = {}
    local poly_b = {}

    local ax = poly[#poly-1]
    local ay = poly[#poly ]
    for i = 1, #poly, 2 do
    local bx = poly[i ]
    local by = poly[i+1]
    local abx = bx - ax
    local aby = by - ay
    local max = ax - mx
    local may = ay - my

    local f = max * dy - may * dx
    if f >= 0 then
    poly_a[#poly_a+1] = ax
    poly_a[#poly_a+1] = ay
    end
    if f <= 0 then
    poly_b[#poly_b+1] = ax
    poly_b[#poly_b+1] = ay
    end

    -- intersect
    local det = dx*aby - dy*abx
    if math.abs(det) > 0.0001 then -- not parallel
    local d = (max*dy - may*dx) / det
    if d and d > 0 and d < 1 then
    local sx = ax + (bx - ax) * d
    local sy = ay + (by - ay) * d
    poly_a[#poly_a+1] = sx
    poly_a[#poly_a+1] = sy
    poly_b[#poly_b+1] = sx
    poly_b[#poly_b+1] = sy
    end
    end
    ax = bx
    ay = by
    end
    if #poly_a < 6 then poly_a = nil end
    if #poly_b < 6 then poly_b = nil end
    return poly_a, poly_b
    end


    -- input: two concave polygons
    -- output: list of concave making up the difference
    function subtractPoly(minuend, subtrahend)
    local result = {}
    local bar = minuend
    local foo
    local ax = subtrahend[#subtrahend-1]
    local ay = subtrahend[#subtrahend ]
    for i = 1, #subtrahend, 2 do
    local bx = subtrahend[i ]
    local by = subtrahend[i+1]
    foo, bar = splitPoly(bar, ax, ay, bx - ax, by - ay)
    if foo then result[#result+1] = foo end
    if not bar then return { minuend } end
    ax = bx
    ay = by
    end
    return result
    end



    poly = {}
    brush = {}
    for i = 1, 16 do
    poly[i*2-1] = 200 + math.floor(math.cos(i / 8 * math.pi) * 100)
    poly[i*2 ] = 200 + math.floor(math.sin(i / 8 * math.pi) * 100)

    brush[i*2-1] = math.floor(math.cos(i / 8 * math.pi) * 80)
    brush[i*2 ] = math.floor(math.sin(i / 8 * math.pi) * 80)
    end



    function love.draw()
    local mx, my = love.mouse.getPosition()

    local subtr = {}
    for i = 1, #brush, 2 do
    subtr[i ] = brush[i ] + mx
    subtr[i+1] = brush[i+1] + my
    end

    G.setLineWidth(3)
    G.setColor(255, 255, 255, 30)
    G.polygon("line", subtr)

    local ps = subtractPoly(poly, subtr)
    for _, p in ipairs(ps) do

    G.setColor(255, 255, 255, 30)
    G.polygon("fill", p)
    G.setColor(255, 255, 255)
    G.setLineWidth(1)
    G.polygon("line", p)
    end
    end