WS2812 "matrix" + Graphics (invert direction)

Hi all,
I have a short test LED-matrix (6x6)
It is arranged in zigzag order starting at top right going left down.

06<05<04<03<02<01
07>08>09>10>11>12
18<17<16<15<14<13
19>20>21>22>23>24
30<29<28<27<26<25
31>32>33>34>35>36

How can I configure the Graphics to have correct coordinates?
This is my current source code:

SPI2.setup({baud:3200000, mosi:B15});
var leds = Graphics.createArrayBuffer(6,6,24,{zigza­g:true, color_order:'bgr'}); 
leds.flip = function() { SPI2.send4bit(leds.buffer, 0b0001, 0b0011); };
leds.clear();
// some text
leds.setColor(0.1,0.1,0.1);
leds.drawString("L",0,0);
leds.flip();

My result is following:

.....X
.....X
.....X
.....X
...XXX
......

But I expect this:

X.....
X.....
X.....
X.....
XXX...
......