opengl 用中点分割算法裁剪直线 代码

中点分割算法是一种经典的线段裁剪算法，可以用于 OpenGL 中对直线的裁剪。下面是使用中点分割算法裁剪直线的代码：

void clipLine(int x0, int y0, int x1, int y1, int xMin, int yMin, int xMax, int yMax) {
    // calculate the region codes of the two endpoints
    int code0 = calculateRegionCode(x0, y0, xMin, yMin, xMax, yMax);
    int code1 = calculateRegionCode(x1, y1, xMin, yMin, xMax, yMax);

    // loop until the line is completely inside the viewport
    while (true) {
        // if both endpoints are inside the viewport, we're done
        if (code0 == INSIDE && code1 == INSIDE) {
            drawLine(x0, y0, x1, y1);
            break;
        }

        // if both endpoints are outside the same edge, the line is completely outside
        if ((code0 & code1) != 0) {
            break;
        }

        // determine which endpoint is outside and clip it against the viewport
        int x, y, code;
        if (code0 != INSIDE) {
            code = code0;
        } else {
            code = code1;
        }

        if ((code & LEFT) != 0) {
            // clip against the left edge
            x = xMin;
            y = y0 + (y1 - y0) * (xMin - x0) / (x1 - x0);
        } else if ((code & RIGHT) != 0) {
            // clip against the right edge
            x = xMax;
            y = y0 + (y1 - y0) * (xMax - x0) / (x1 - x0);
        } else if ((code & BOTTOM) != 0) {
            // clip against the bottom edge
            x = x0 + (x1 - x0) * (yMin - y0) / (y1 - y0);
            y = yMin;
        } else if ((code & TOP) != 0) {
            // clip against the top edge
            x = x0 + (x1 - x0) * (yMax - y0) / (y1 - y0);
            y = yMax;
        }

        if (code == code0) {
            x0 = x;
            y0 = y;
            code0 = calculateRegionCode(x0, y0, xMin, yMin, xMax, yMax);
        } else {
            x1 = x;
            y1 = y;
            code1 = calculateRegionCode(x1, y1, xMin, yMin, xMax, yMax);
        }
    }
}

int calculateRegionCode(int x, int y, int xMin, int yMin, int xMax, int yMax) {
    int code = INSIDE;

    if (x < xMin) {
        code |= LEFT;
    } else if (x > xMax) {
        code |= RIGHT;
    }

    if (y < yMin) {
        code |= BOTTOM;
    } else if (y > yMax) {
        code |= TOP;
    }

    return code;
}

其中，`calculateRegionCode` 函数用于计算一个点在视口中的位置，返回一个 4 位二进制数，表示点在视口的哪个边界的哪一侧。`clipLine` 函数则根据两个端点的位置关系，通过循环和裁剪操作，将直线裁剪成在视口内的部分，并调用 `drawLine` 函数绘制。