Help with drawing lines

Hi,
I need to draw a various types of lines, and I have a problem with drawing
dashed lines with width greater then 1 pixel.

Here is my code:

#include "gd.h"
#include <stdio.h>

int main() {

gdImagePtr im;
int styleDotted[2], styleDashed[6];
FILE * jpegout;
int black;
int red;
 im = gdImageCreate(100, 100);
 black = gdImageColorAllocate(im, 0, 0, 0);
red = gdImageColorAllocate(im, 255, 0, 0);

styleDashed[0] = red;
styleDashed[1] = red;
styleDashed[2] = red;
styleDashed[3] = red;
styleDashed[4] = gdTransparent;
styleDashed[5] = gdTransparent;

gdImageSetThickness(im, 2);
gdImageSetStyle(im, styleDashed, 6);
gdImageLine(im, 0, 12, 99, 12, gdStyled);
 jpegout = fopen("test3.jpg", "wb");
gdImageJpeg(im, jpegout, -1);

fclose(jpegout);

gdImageDestroy(im);

return 0;
}

Image created with this program is in attachment. Did I miss something, or
what?

Thanks in advance.