[cairo] Repeating gradient patterns

[J. Ali Harlow]

Guys,

I'm trying to use repeating gradient patterns to draw the background 
for a matrix of 27x27 cells. Cells are labelled with two colours. I 
want to show these by placing the first colour in the top-left corner 
and the second colour in the bottom-right corner. The obvious way to do 
that in cairo seems to be to use a gradient pattern. However, I have 
two problems:

* The period of the repeating patterns seems to be too small. If you 
just run your eye from the top-left cell down the diagonal to the 
bottom-right this is quite obvious.

* Half the cells are drawn as expected with the colour stops in the 
corners. The other half have the colour stops in the middle.

I attach a test problem to show what I am doing as well as it's output 
(png). Any pointers as to what I'm doing wrong would be much 
appreciated.

Thanks,

Ali.
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