# Quick start: design a logo

julia> ] add Luxor

# A first drawing

The new (and currently fictitious) organization JuliaFission has just asked you to design a new logo for them. They're something to do with atoms and particles, perhaps? So we'll design a new logo for them using some basic shapes; perhaps colored circles in some kind of spiral formation would look suitably "atomic".

Let's try out some ideas.

using Luxor
Drawing(500, 500, "my-drawing.svg")
origin()
setcolor("red")
circle(Point(0, 0), 100, action = :fill)
finish()
preview()

This short piece of code does the following things:

• makes a new drawing 500 units square, and will save it in the file "my-drawing.svg" in SVG format.

• moves the zero point from the top left to the center. Graphics applications usually start measuring from the top left (occasionally from the bottom left), but it's easier to work out the positions of things if you start at the center. The origin() function moves the 0/0 point to the center of the drawing.

• selects one of the 200 or so named colors (defined in Colors.jl)

• draws a circle at x = 0, y = 0, with radius 100 units, and fills it with the current color

• finishes the drawing and displays it on the screen

In case you're wondering, the units are points (as in font sizes), and there are 72 points in an inch, just over 3 per millimeter. The y-axis points down the page. If you want to be reminded of where the x and y axes are, use the rulers function.

The action=:fill at the end of circle uses one of a set of symbols that let you use the shape you've created in different ways. There's the :stroke action, which draws around the edges but doesn't fill the shape with color. You might also meet the :fillstroke, :fillpreserve, :strokepreserve, :clip, and :path actions.

## Circles in a spiral

We want more than just one circle. We'll define a triangular shape, and place a circle at each corner. The ngon function creates regular polygons (eg triangles, squares, pentagons, etc.), and the vertices=true keyword doesn't draw the shape, it just provides the corner points - just what we want.

# using Luxor
Drawing(500, 500, "my-drawing.svg")
origin()
setcolor("red")
corners = ngon(Point(0, 0), 80, 3, vertices=true)
circle.(corners, 10, action = :fill)
finish()
preview()

Notice the "." after circle. This broadcasts the circle() function over the corners, thus drawing a 10-unit red-filled circle at every point.

The arguments to ngon are usually centerpoint, radius, and the number of sides. Try changing the third argument from 3 (triangle) to 4 (square) or 31 (traikontagon?).

To create a spiral of circles, we want to repeat this "draw a circle at each vertex of a triangle" procedure more than once. A simple loop will do: we'll rotate the drawing by i * 5° (deg2rad(5) radians) each time (so 5°, 10°, 15°, 20°, 25°, and 30°), and at the same time increase the size of the polygon by multiples of 10:

Drawing(500, 500, "my-drawing.svg")
origin()

setcolor("red")
for i in 1:6
corners = ngon(Point(0, 0), 80 + 10i, 3, vertices=true)
circle.(corners, 10, action = :fill)
end

finish()
preview()

The colors used in the Julia logo are available as constants in Luxor, so we can make two changes that cycle through them. The first new line creates the set of Julia colors; then the setcolor function then works through them. mod1 (get the nth element of an array) is the 1-based version of the mod function, essential for working with Julia and its 1-based indexing, such that mod1(4, end) gets the last value of a four element array (whereas mod(4, end) would fail, since it would return 0, and colors[0] would be an error).

using Luxor
using Colors

Drawing(500, 500, "my-drawing.svg")
origin()

const colors = (Luxor.julia_green, Luxor.julia_red,Luxor.julia_purple, Luxor.julia_blue)

for i in 1:6
setcolor(colors[mod1(i, end)])
corners = ngon(Point(0, 0), 80 + 10i, 3, vertices=true)
circle.(corners, 10, action = :fill)
end

finish()
preview()


## Taking particles seriously

The flat circles are a bit dull, so let's write a function that draws the circles as ‘particles’. The drawcircle() function draws lots of circles on top of each other, but each one is drawn with a slightly smaller radius and a slightly lighter shade of the incoming color. The rescale function in Luxor provides an easy way to map or adjust values from one range to another. Here, numbers between 5 and 1 are mapped to numbers between 0.5 and 3. And the radius is scaled to run between radius and radius/6. Also, let's make them get larger as they spiral outwards, by adding 4i to the radius when called by drawcircle().

function drawcircle(pos, radius, n)
c = colors[mod1(n, end)]
for i in 5:-0.1:1
setcolor(rescale(i, 5, 1, 0.5, 3) .* c)
circle(pos + (i/2, i/2), rescale(i, 5, 1, radius, radius/6), action = :fill)
end
end

Drawing(500, 500, "my-drawing.svg")
origin()

for i in 1:6
corners = ngon(Point(0, 0), 80 + 10i, 3, vertices=true)
drawcircle.(corners, 10 + 4i, i)
end

finish()
preview()

This is looking quite promising. But here’s the thing: in a parallel universe, you might already have made this in no time at all using Adobe Illustrator or Inkscape. But with this Luxor code, you can try all kinds of different variations with almost immediate results - you can “walk through the parameter space”, either manually or via code, and see what effects you get. You don’t have to redraw everything with different angles and radii...

So here's what a pentagonal theme with more circles looks like:

Drawing(500, 500, "my-drawing.svg")
origin()

for i in 1:12
preview()