Function TkLineToArea

micropolis-activity/src/tk/tktrig.c:156–273

(end1Ptr, end2Ptr, rectPtr)

 *
 *--------------------------------------------------------------
 */

int
TkLineToArea(end1Ptr, end2Ptr, rectPtr)
    double end1Ptr[2];		/* X and y coordinates for one endpoint
				 * of line. */
    double end2Ptr[2];		/* X and y coordinates for other endpoint
				 * of line. */
    double rectPtr[4];		/* Points to coords for rectangle, in the
				 * order x1, y1, x2, y2.  X1 must be no
				 * larger than x2, and y1 no larger than y2. */
{
    int inside1, inside2;

    /*
     * First check the two points individually to see whether they
     * are inside the rectangle or not.
     */

    inside1 = (end1Ptr[0] >= rectPtr[0]) && (end1Ptr[0] <= rectPtr[2])
	    && (end1Ptr[1] >= rectPtr[1]) && (end1Ptr[1] <= rectPtr[3]);
    inside2 = (end2Ptr[0] >= rectPtr[0]) && (end2Ptr[0] <= rectPtr[2])
	    && (end2Ptr[1] >= rectPtr[1]) && (end2Ptr[1] <= rectPtr[3]);
    if (inside1 != inside2) {
	return 0;
    }
    if (inside1 & inside2) {
	return 1;
    }

    /*
     * Both points are outside the rectangle, but still need to check
     * for intersections between the line and the rectangle.  Horizontal
     * and vertical lines are particularly easy, so handle them
     * separately.
     */

    if (end1Ptr[0] == end2Ptr[0]) {
	/*
	 * Vertical line.
	 */
    
	if (((end1Ptr[1] >= rectPtr[1]) ^ (end2Ptr[1] >= rectPtr[1]))
		&& (end1Ptr[0] >= rectPtr[0])
		&& (end1Ptr[0] <= rectPtr[2])) {
	    return 0;
	}
    } else if (end1Ptr[1] == end2Ptr[1]) {
	/*
	 * Horizontal line.
	 */
    
	if (((end1Ptr[0] >= rectPtr[0]) ^ (end2Ptr[0] >= rectPtr[0]))
		&& (end1Ptr[1] >= rectPtr[1])
		&& (end1Ptr[1] <= rectPtr[3])) {
	    return 0;
	}
    } else {