Question

How to optimize this line drawing routine ? Will memcpy work faster ?

void ScreenDriver::HorizontalLine(int wXStart, int wXEnd, int wYPos,
    COLORVAL Color, int wWidth)
{
    int iLen = wXEnd - wXStart + 1;

    if (iLen <= 0)
    {
        return;
    }
    while(wWidth-- > 0)
    {
        COLORVAL *Put = mpScanPointers[wYPos] + wXStart;
        int iLen1 = iLen;

        while(iLen1--)
        {
            *Put++ = Color;
        }
        wYPos++;
    }
}

Answer 1

I think you mean to say “memset” instead of “memcpy”. Replacing this bit of the code:

while (iLen--)
{
    *Put++ = Color;
}

with

memset(Put, Color, iLen);

could be faster but so much depends on your target CPU, memory architecture and the typical values of iLen encountered. It’s not likely to be a big win, but if you’ve got the time I encourage you to measure the alternatives as that kind of exercise is the only way to really understand optimization.

Of course, this memset() use will only work if COLORVAL is character sized.