# Mexican Blanket (#127)

**URL:** <https://www.ruby-forum.com/t/mexican-blanket-127/106834>\
**Category:** Ruby\
**Created:** [June 14, 2007, 2:16pm UTC](https://www.ruby-forum.com/t/mexican-blanket-127/106834 "2007-06-14T14:16:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![bbazzarrakk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/47e85d/32.png) [@bbazzarrakk](https://www.ruby-forum.com/u/bbazzarrakk)\
**Post date:** [June 14, 2007, 2:16pm UTC](https://www.ruby-forum.com/t/mexican-blanket-127/106834/1 "2007-06-14T14:16:22Z")

</div>

Several solutions to this quiz called out to RMagick to draw pictures of  
their  
work. That made for some pretty output. One such solution was from  
Justin  
Ethier and I want to take a look at that code.

Justin observed that each row of the pattern is just the previous row  
shifted  
over one pixel. In order to build those rows, Justing decided to just  
build one  
long pattern and slice it as needed. Here’s that chunk of code:

def create\_gradient(colors, width=5)  
pattern = []

for i in 0…(width)  
(width-i).times { pattern.push(colors[0]) }  
(i+1).times { pattern.push(colors[1]) }  
end

for i in 0…(width)  
(i+1).times { pattern.push(colors[2]) }  
(width-i-1).times { pattern.push(colors[1]) }  
end

pattern  
end

# …

You pass this method an Array of three colors and a width for a full  
band of  
color. It begins by fading the first color into the second by  
iteratively  
adding thinner and thinner lines to the gradient pattern. It then  
repeats the  
process in reverse to fade the second color into the third.

Justin’s blankets also include solid color bands created by the  
following  
method:

# …

def create\_solid(colors, width)  
pattern = []  
for color in colors  
width.times { pattern.push(color) }  
end  
pattern  
end

# …

This methods works exactly like create\_gradient() except there’s no  
blending of  
colors.

With the pieces to create the structure in place, we are now ready for  
some  
rendering code:

# …

def draw\_ascii(pattern, width)  
for i in 0…(pattern.size-width+1)  
puts pattern.slice(i, width).join  
end  
end

# …

As you can see, generating the ASCII output is trivial. The long  
pattern is  
simply divided into a moving window of width slices. Each slice is then  
printed  
as one row of output.

RMagick rendering takes a little more work, but still isn’t hard:

# …

require ‘RMagick’  
include Magick

def draw(filename, pattern, width, height)  
canvas = Magick::ImageList.new  
canvas.new\_image(width, height, Magick::HatchFill.new(‘white’,  
‘white’))  
pts = Magick::Draw.new

for y in 0… height  
line = pattern.slice(y, width)

```
 x = 0
 for color in line
   pts.fill(color)
   pts.point(x, y)
   x = x + 1
 end

```

end

pts.draw(canvas)  
canvas.write(filename)  
end

# …

This method begins by preparing a canvas on which it can draw points.  
From  
there it does the same looping over the pattern we saw earlier, but this  
time  
points are plotted on the canvas. When all the marks have been made,  
the image  
is flushed to a file on the disk.

The last bit of code puts the generators and renderers to work:

# …

draw\_ascii(create\_gradient([‘R’, ‘B’, ‘Y’]), 28)

mex\_flag = create\_solid([‘rgb(0, 64, 0)’, ‘white’, ‘red’], 5)  
border = create\_solid([‘rgb(0, 64, 0)’], 25)

pattern = create\_gradient([‘red’, ‘blue’, ‘yellow’])  
pattern = pattern + mex\_flag  
pattern = pattern + border  
pattern = pattern + create\_gradient([‘black’, ‘red’, ‘orange’])  
pattern = pattern + border  
pattern = pattern + mex\_flag.reverse  
pattern = pattern + create\_gradient([‘red’, ‘purple’, ‘black’], 8)  
draw(“mexican\_blanket.jpg”, pattern, 100, 200)

You can see here that the ASCII renderer is fed a trivial pattern  
created from a  
single gradient. The pattern built for the image file is more complex,  
combining several different patterns. In both cases though, it’s a  
single call  
to the drawing routines we examined above to show results.

My thanks to all the weavers. I’ll bet you never knew you had such a  
talent for  
fabric.

Tomorrow we will try some non-traditional arithmetic…