图形学-直线算法

浏览数：24 / 时间：2015年06月08日

图形学算法：DDA（Digital Differential Analyzer）

void lineDDA(int x0, int y0, int xEnd, int yEnd)
{
    float dx = xEnd - x0, dy = yEnd - y0, steps, k;
    float xInerement, yInerement, x = x0, y = y0;

    if (fabs(dx) > fabs(dy))
    {
        steps = fabs(dx);
    }
    else
    {
        steps = fabs(dy);
    }

    xInerement = float(dx) / float(steps);
    yInerement = float(dy) / float(steps);

    setPixel(round(x), round(y));

    for (k = 0; k < steps; k++)
    {
        x += xInerement;
        y += yInerement;
        setPixel(round(x), round(y));
    }
}

效果图：
技术分享

效果很差，线段部分不连续。

2. Bresenham‘s Line Algorithm

" We need to decide which of two possible pixel positions is closer to the line path at each sample step.
" Testing the sign of an integer parameter whose value is proportional to the difference between the vertical
vertical separations of the two pixel positions from the actual line path.

void lineBres(int x0, int y0, int xEnd, int yEnd)
{
    int dx = abs(xEnd - x0), dy = abs(yEnd - y0);
    int p = 2 * dy - dx;
    int twoDy = 2 * dy, twoDyMinusDx = 2 * (dy - dx);
    int x, y;

    if (x0 > xEnd)
    {
        x = xEnd; 
        y = yEnd;
        xEnd = x0;
    }
    else
    {
        x = x0;
        y = y0;
    }

    setPixel(x, y);
    
    while (x < xEnd)
    {
        x++;
        if (p < 0)
            p += twoDy;
        else
        {
            y++;
            p += twoDyMinusDx;
        }

        setPixel(x, y);
    }
}