""" draw_line(canvas, p1, p2)
Draw a white line segment between points p1 and p2 in canvas.
    Canvas is an image of RGB{Float32}
    p1 and p2 are 2-tuples of Int
    The slope of the line is between 0 and 1.
"""
function draw_line(canvas, p1, p2)
    white = RGB{Float32}(1.0, 1.0, 1.0)

    # TODO 1 and 2

end # draw_line (no color)

""" draw_line(canvas, p1, p2, v1, v2)
Draw a line segment between points p1 and p2 in canvas, 
interpolating its color between v1 and v2.
    Canvas is an image of RGB{Float32}
    p1 and p2 are 2-tuples of Int
    v1 and v2 are colors of type RGB{Float32}
    The slope of the line is between 0 and 1.
"""
function draw_line(canvas, p1, p2, v1, v2)

    # TODO 3
end # draw_line (with color)

function task1test()

    canvas = zeros(RGB{Float32}, 600, 600)

    p1 = (4,10)

    for theta = 0:1:45
        x = round(10 + 500*cosd(theta))
        y = round(10 + 500*sind(theta))
        draw_line(canvas, (10, 10), (x, y));
    end

    canvas = transpose(canvas[:, end:-1:1])
    save("t1out.png", canvas)
    canvas
end # task1test

function task3test()

    canvas = zeros(RGB{Float32}, 600, 600)

    for y2 = 10:10:510
        v = y2/510
    
        start_color = RGB{Float32}(0.2, 1.0-v, y2/510)
        end_color = RGB{Float32}(0.2, y2/510, 1.0-v)
        draw_line(canvas, (10, 10), (510, y2), start_color, end_color)
    end

    canvas = transpose(canvas[:, end:-1:1])

    save("t3out.png", canvas)
    canvas
end # task3test