LÖVE

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function testLineRect(a, b)
  -- line vector
  local dx, dy = a.x2 - a.x, a.y2 - a.y
  -- line halflength vector
  local hdx, hdy = dx/2, dy/2
  -- line midpoint
  local mx, my = a.x + hdx, a.y + hdy
  -- translate midpoint to rect origin
  mx, my = mx - b.x, my - b.y
  
  -- separating axes tests
  local ahdx = abs(hdx)
  if abs(mx) > b.hw + ahdx then
    return
  end
  local ahdy = abs(hdy)
  if abs(my) > b.hh + ahdy then
    return
  end

  -- wedge product test (cross product in 2D)
  local cross1 = b.hw*ahdy + b.hh*ahdx
  local cross2 = abs(mx*hdy - my*hdx)
  if cross2 > cross1 then
    return
  end

  -- collision normal is the line rotated by 90 degrees
  local d = sqrt(dx*dx + dy*dy)
  local nx, ny = dy/d, -dx/d
  
  -- allow passing through one side of the line
  local vx = (a.xv or 0) - (b.xv or 0)
  local vy = (a.yv or 0) - (b.yv or 0)
  local dot = vx*nx + vy*ny
  if dot > 0 then
    return
  end

  -- todo: WHAT'S THE PENETRATION DEPTH?
  local pen = ???

  return nx, ny, pen
end