drawingAPI

local function drawTri(p1,p2,p3,c,pr) --Called to draw a triangle, given three points, a peripheral (pr), and a color (c).
    if p2.y < p1.y then p1,p2 = p2,p1 end --sort points
    if p3.y < p2.y then p2,p3 = p3,p2 end
    if p2.y < p1.y then p1,p2 = p2,p1 end

    if p1.y == p2.y then --natural flat top
        if p2.x < p1.x then p1,p2 = p2,p1 end
        drawFlatBottom(p1,p2,p3,c,pr)
    elseif p2.y == p3.y then --natural flat bottom
        if p3.x < p2.x then p2,p3 = p3,p2 end
        drawFlatBottom(p1,p2,p3,c,pr)
    else
            --splitting vertex
        local alphaSplit = (p2.y - p1.y) / (p3.y - p1.y)
        local vi ={
            x = p1.x + ((p3.x - p1.x) * alphaSplit),
            y = p1.y + ((p3.y - p1.y) * alphaSplit),
            z = p1.z + ((p3.z - p1.z) * alphaSplit) }
        if pv2.x < vi.x then --Major right
            drawFlatBottom(p1,p2,vi,c,pr)
            drawFlatTop(p2,vi,p3,c,pr)
        else --Major left
            drawFlatBottom(p1,vi,p2,c,pr)
            drawFlatTop(vi,p2,p3,c,pr)
        end
    end
end

local function pPixel() end --draw a pixel at coodinates x,y with color c, to a peripheral (pr)

local function pPixelTerm(x,y,c)
    term.setCursorPos(x,y)
    term.setBackgroundColor(c)
    print(" ")
end

local function pPixelMon(x,y,c,pr)
    pr.setCursorPos(x,y)
    pr.setCursorPos(c)
    print(" ")
end

local function pPixelAR(x,y,c,pr)
    pr.horizontalLine(x, x, y, c)
end

local function drawFlatTriangle() end --switches between terminal output and AR goggle output depending on bind mode.

local function drawFlatTriangleCC(xStart,xEnd,y,c,pr)
    for x = xStart, xEnd do
        pPixel(x,y,c,pr)
    end
end

local function drawFlatTriangleAR(xStart,xEnd,y,c,pr)
    pr.horizontalLine(xStart, xEnd, y, c)
end

local function drawFlatBottom(p1,p2,p3,c,pr) --Draw the top portion of a triangle with a flat bottom.
    local slope1 = (p2.x - p1.x) / (p2.y - p1.y)
    local slope2 = (p3.x - p1.x) / (p3.y - p1.y)
    for y = p1.y, p3.y do
        local yP1 = (y+p1.y)
        local xStart = slope1 * yP1 + p1.x
        local xEnd =   slope2 * yP1 + p1.x
        drawFlatTriangle(xStart,xEnd,y,c,pr)
    end
end

local function drawFlatTop(p1,p2,p3,c,pr) --Draw the bottom portion of a triangle with a flat top.
    local slope1 = (p3.x - p1.x) / (p3.y - p1.y)
    local slope2 = (p3.x - p2.x) / (p3.y - p2.y)
    for y = p1.y, p3.y do
        local xStart = slope1 * (y - p1.y) + p1.x
        local xEnd =   slope2 * (y - p2.y) + p2.x
        drawFlatTriangle(xStart,xEnd,y,c,pr)
    end
end

local function bindOutputMode(mode) --This switches drawing functions between Advanced peripherals AR goggles and Terminal output.
    if mode == "term" then
        drawFlatTriangle = drawFlatTriangleCC
        pPixel = pPixelTerm
    elseif mode == "mon" then
        drawFlatTriangle = drawFlatTriangleCC
        pPixel = pPixelMon
    elseif mode == "AR" then
        drawFlatTriangle = drawFlatTriangleAR
        pPixel = pPixelAR
    else error("invalid mode ("..mode..") for bindTriMode. Please use either 'term', 'mon', or 'AR'.") end
end

return {
    bindOutputMode = bindOutputMode,
    drawTri = drawTri,
}