Simple collision detection routines

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-- GENERAL COLLISION ROUTINES --------------------------------

local class    = {}

local mathAbs = math.abs

function class.pointInRect( pointX, pointY, left, top, width, height )
    if pointX >= left and pointX <= left + width and pointY >= top and pointY <= top + height then return true
    else                                                                                           return false ; end
end
function class.pointInCircle( pointX, pointY, centerX, centerY, radius )
    local dX, dY = pointX - centerX, pointY - centerY
    if dX * dX + dY * dY <= radius * radius then return true
    else                                         return false ; end
end
function class.pointInDiamond( pointX, pointY, centerX, centerY, radius )
    if mathAbs( pointX - centerX ) + mathAbs( pointY - centerY ) <= radius then return true
    else                                                                        return false ; end
end
function class.rectInRect( left1, top1, width1, height1, left2, top2, width2, height2 )
    if left1 >= left2 and left1 + width1 <= left2 + width2 and top1 >= top2 and top1 + height1 <= top2 + height2 then return true
    else                                                                                                              return false ; end
end
function class.circleInCircle( centerX1, centerY1, radius1, centerX2, centerY2, radius2 )
    if radius1 > radius2 then return false ; end
    local dX, dY, radii = centerX1 - centerX2, centerY1 - centerY2, radius2 - radius1
    if dX * dX + dY * dY <= radii * radii then return true
    else                                       return false ; end
end
function class.diamondInDiamond( centerX1, centerY1, radius1, centerX2, centerY2, radius2 )
    if radius1 > radius2 then return false ; end
        if mathAbs( centerX1 - centerX2 ) + mathAbs( centerY1 - centerY2 ) <= radius2 - radius1 then return true
    else                                                                                   return false ; end
end
function class.intersectRects( left1, top1, width1, height1, left2, top2, width2, height2 )
    if left1 + width1 >= left2 and left1 <= left2 + width2 and top1 + height1 >= top2 and top1 <= top2 + height2 then return true
    else                                                                                                              return false ; end
end
function class.intersectCircles( centerX1, centerY1, radius1, centerX2, centerY2, radius2 )
    local dX, dY, radii = centerX1 - centerX2, centerY1 - centerY2, radius1 + radius2
    if dX * dX + dY * dY <= radii * radii then return true
    else                                       return false ; end
end
function class.intersectDiamonds( centerX1, centerY1, radius1, centerX2, centerY2, radius2 )
    if mathAbs( centerX1 - centerX2 ) + mathAbs( centerY1 - centerY2 ) <= radius1 + radius2 then return true
    else                                                                                   return false ; end
end
function class.intersectRectWithCircle( left, top, width, height, centerX, centerY, radius )

    -- Are you within the rectangular extensions?
    if left <= centerX and left + width >= centerX then
        if top + height >= centerY - radius and top <= centerY + radius then return true
        else                                                                 return false ; end
    elseif top <= centerY and top + height >= centerY then
        if left + width >= centerX - radius and left <= centerX + radius then return true
        else                                                                  return false ; end
    else

        -- Curved bits - split into the 4 corner checks
        if left < centerX then
            if top < centerY then return class.pointInCircle( left + width, top + height, centerX, centerY, radius )
            else                  return class.pointInCircle( left + width, top, centerX, centerY, radius ) ; end
        else
            if top < centerY then return class.pointInCircle( left, top + height, centerX, centerY, radius )
            else                  return class.pointInCircle( left, top, centerX, centerY, radius ) ; end
        end
    end

end
function class.intersectRectWithDiamond( left, top, width, height, centerX, centerY, radius )

    -- Are you within the rectangular extensions?
    if left <= centerX and left + width >= centerX then
        if top + height >= centerY - radius and top <= centerY + radius then return true
        else                                                                 return false ; end
    elseif top <= centerY and top + height >= centerY then
        if left + width >= centerX - radius and left <= centerX + radius then return true
        else                                                                  return false ; end
    else

        -- Diagonal bits - split into the 4 corner checks
        if left < centerX then
            if top < centerY then return class.pointInDiamond( left + width, top + height, centerX, centerY, radius )
            else                  return class.pointInDiamond( left + width, top, centerX, centerY, radius ) ; end
        else
            if top < centerY then return class.pointInDiamond( left, top + height, centerX, centerY, radius )
            else                  return class.pointInDiamond( left, top, centerX, centerY, radius ) ; end
        end
    end

end

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return class