Function EntryScanTo

micropolis-activity/src/tk/tkentry.c:1362–1396

(entryPtr, x)

 *
 *	Given a y-coordinate (presumably of the curent mouse location)
 *	drag the view in the window to implement the scan operation.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The view in the window may change.
 *
 *----------------------------------------------------------------------
 */

static void
EntryScanTo(entryPtr, x)
    register Entry *entryPtr;		/* Information about widget. */
    int x;				/* X-coordinate to use for scan
					 * operation. */
{
    int newLeftIndex;

    /*
     * Compute new leftIndex for entry by amplifying the difference
     * between the current position and the place where the scan
     * started (the "mark" position).  If we run off the left or right
     * side of the entry, then reset the mark point so that the current
     * position continues to correspond to the edge of the window.
     * This means that the picture will start dragging as soon as the
     * mouse reverses direction (without this reset, might have to slide
     * mouse a long ways back before the picture starts moving again).
     */

    newLeftIndex = entryPtr->scanMarkIndex
	    - (10*(x - entryPtr->scanMarkX))/entryPtr->avgWidth;
    if (newLeftIndex >= entryPtr->numChars) {
	newLeftIndex = entryPtr->scanMarkIndex = entryPtr->numChars-1;
	entryPtr->scanMarkX = x;
    }
    if (newLeftIndex < 0) {
	newLeftIndex = entryPtr->scanMarkIndex = 0;