polyDrawingMonitor_API_thing

--CODE BY JIG487

local function drawFlatTriangle(peripheralWrapper,px1,px2,y,color)
    local xStart = math.ceil(px1 - 0.5)
    local xEnd =   math.ceil(px2 - 0.5)

        --only draw positive coordinates
    for x = xStart, xEnd do
        if y > 0 and x > 0 then
            peripheralWrapper.setCursorPos(x,y)
            peripheralWrapper.setBackgroundColor(color)
            peripheralWrapper.write(" ")
        end
    end
end

local function drawFlatTopTriangle( peripheralWrapper,vec1,vec2,vec3,color)
        --Calculate slopes in screen space
        --Run over rise so we don't get infinite slopes
    local m1 = (vec3.x - vec1.x) / (vec3.y - vec1.y)
    local m2 = (vec3.x - vec2.x) / (vec3.y - vec2.y)

        --Calculate start and end scanlines
    local yStart = math.ceil(vec1.y - 0.5)
    local yEnd =   math.ceil(vec3.y - 0.5)-1 --the scanline AFTER the last line drawn, which is why it's offset by -1

    for y = yStart, yEnd do
        --calculate start and end x's
        --Add 0.5 because we're calculating based on pixel centers
        local px1 = m1 * (y + 0.5 - vec1.y) + vec1.x
        local px2 = m2 * (y + 0.5 - vec2.y) + vec2.x

        drawFlatTriangle( peripheralWrapper,px1,px2,y,color)
    end
end

    --refer to drawFlatTopTriangle for comments
local function drawFlatBottomTriangle( peripheralWrapper,vec1,vec2,vec3,color)
    local m1 = (vec2.x - vec1.x) / (vec2.y - vec1.y)
    local m2 = (vec3.x - vec1.x) / (vec3.y - vec1.y)
    local yStart = math.ceil(vec1.y-0.5)
    local yEnd =   math.ceil(vec3.y-0.5)-1
    for y = yStart, yEnd do
        local px1 = m1 * (y + 0.5 - vec1.y) + vec1.x
        local px2 = m2 * (y + 0.5 - vec1.y) + vec1.x
        drawFlatTriangle( peripheralWrapper,px1,px2,y,color)
    end
end

    --Draws a solid triangle from 3 vectors with an X and a Y
    --Splits up the triangle into 2 triangles: a flat top and a flat bottom.
    --Takes in a peripheral wrapper, 3 vectors, and a color to draw the whole thing as.
local function drawSolidTriangle( peripheralWrapper,vec1,vec2,vec3,color)

        --using pointers so we can swap (for sorting purposes) probably don't need this b/c lua? idk
    local pv1 = vec1
    local pv2 = vec2
    local pv3 = vec3

        --Sort vertices by y
    if pv2.y < pv1.y then pv1,pv2 = pv2,pv1 end
    if pv3.y < pv2.y then pv2,pv3 = pv3,pv2 end
    if pv2.y < pv1.y then pv1,pv2 = pv2,pv1 end

    if pv1.y == pv2.y then --Natural flat top
            --Sort top vertice by x
        if pv2.x < pv1.x then pv1,pv2 = pv2,pv1 end
        drawFlatTopTriangle(peripheralWrapper,pv1,pv2,pv3,color )

    elseif pv2.y == pv3.y then --Natural flat bottom
            --Sort bottom vertice by x
        if pv3.x < pv2.x then pv3,pv2 = pv2,pv3 end
        drawFlatBottomTriangle(peripheralWrapper,pv1,pv2,pv3,color)

    else --General triangle
        local alphaSplit = (pv2.y-pv1.y)/(pv3.y-pv1.y)
        local vi ={
            x = pv1.x + ((pv3.x - pv1.x) * alphaSplit),
            y = pv1.y + ((pv3.y - pv1.y) * alphaSplit), }
        if pv2.x < vi.x then --Major right
            drawFlatBottomTriangle(peripheralWrapper,pv1,pv2,vi,color)
            drawFlatTopTriangle(peripheralWrapper,pv2,vi,pv3,color)
        else --Major left
            drawFlatBottomTriangle(peripheralWrapper,pv1,vi,pv2,color)
            drawFlatTopTriangle(peripheralWrapper,vi,pv2,pv3,color)
        end
    end
end

return {
    drawSolidTriangle = drawSolidTriangle,
}