I don't normally post code, but this is straight out of the Microchip 
Graphics Library SSD1926 driver (SSD1926.h).  While this is a bug, it's 
really more of a typo.  The thing is, it put a line on my display where 
one shouldn't have been, and it took me almost 2 hours to find it.  The 
last line below is

    SetReg(REG_2D_1f1, (y1 >> 8) & 0xFF);

and should be

    SetReg(REG_2D_1f1, (y2 >> 8) & 0xFF);

Makes all the difference in the world esp. when your y dimension is 
larger than 255.  If I were operating in landscape on this particular 
display, I never would have seen it, and that's probably how it got out 
without being fixed.  What are the normal channels for reporting this 
kind of thing to Microchip?  Do I get a cookie?

Thanks,

Tony

// From SSD1926.c packaged in the Microchip Graphics Library release 
version 1.75

static WORD Line2D(SHORT x1, SHORT y1, SHORT x2, SHORT y2)
{
    #ifndef USE_NONBLOCKING_CONFIG
        while(IsDeviceBusy() != 0); /* Ready */
    #else
        if(IsDeviceBusy() != 0) return 0;
    #endif

/* Line Boundaries */
    SetReg(REG_2D_1e4, x1 & 0xFF);
    SetReg(REG_2D_1e5, (x1 >> 8) & 0xFF);
    SetReg(REG_2D_1e8, y1 & 0xFF);
    SetReg(REG_2D_1e9, (y1 >> 8) & 0xFF);
    SetReg(REG_2D_1ec, x2 & 0xFF);
    SetReg(REG_2D_1ed, (x2 >> 8) & 0xFF);
    SetReg(REG_2D_1f0, y2 & 0xFF);
    SetReg(REG_2D_1f1, (y1 >> 8) & 0xFF);
    ....
}
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