/**
* Gets the scale factor that allows us to translate pixel values to scroll bar values and vice
* versa. This assumes that the range of pixels spans from the last pixel of
* <tt>scrollUpButton</tt> to the first pixel of <tt>scrollDownButton</tt> and excludes the pixels
* taken up by <tt>handle</tt>.
*
* <p>To map from scroll bar values (<i>real values</i>) to pixel values, you multiply by the
* value scale. To map from pixel values back to real values, you divide by the value scale.
*
* @return <tt><number of legal pixel values> / <number of legal real values></tt>
*/
private float getValueScale() {
ScrollBar scrollBar = (ScrollBar) getComponent();
float valueScale;
int start = scrollBar.getStart();
int end = scrollBar.getEnd();
int extent = scrollBar.getExtent();
int maxLegalRealValue = end - extent;
int numLegalRealValues = maxLegalRealValue - start + 1;
int numLegalPixelValues;
if (scrollBar.getOrientation() == Orientation.HORIZONTAL) {
int availableWidth = getWidth() - scrollUpButton.getWidth() - scrollDownButton.getWidth() + 2;
numLegalPixelValues = availableWidth - handle.getWidth() + 1;
} else {
int availableHeight =
getHeight() - scrollUpButton.getHeight() - scrollDownButton.getHeight() + 2;
numLegalPixelValues = availableHeight - handle.getHeight() + 1;
}
// the number of segments is one less than the number of values
valueScale = numLegalPixelValues / ((float) numLegalRealValues - 1);
return valueScale;
}
/**
* Initiates automatic block scrolling. This only happens if the handle is visible since whether
* the user clicked before or after the handle determines the direction of the scrolling.
*
* @param component The scroll bar.
* @param button The button that was pressed.
* @param x The x-coordinate of the event in the scroll bar's coordinate space.
* @param y The y-coordinate of the event in the scroll bar's coordinate space.
*/
@Override
public boolean mouseDown(Component component, Mouse.Button button, int x, int y) {
boolean consumed = super.mouseDown(component, button, x, y);
if (button == Mouse.Button.LEFT && handle.isVisible()) {
ScrollBar scrollBar = (ScrollBar) getComponent();
// Begin automatic block scrolling. Calculate the direction of
// the scroll by checking to see if the user pressed the mouse
// in the area "before" the handle or "after" it.
int direction;
int realStopValue;
if (scrollBar.getOrientation() == Orientation.HORIZONTAL) {
direction = x < handle.getX() ? -1 : 1;
int pixelStopValue = x - scrollUpButton.getWidth() + 1;
if (direction == 1) {
// If we're scrolling down, account for the width of the
// handle in our pixel stop value so that we stop as soon
// as the *bottom* of the handle reaches our click point
pixelStopValue -= handle.getWidth();
}
realStopValue = (int) (pixelStopValue / getValueScale());
} else {
direction = y < handle.getY() ? -1 : 1;
int pixelStopValue = y - scrollUpButton.getHeight() + 1;
if (direction == 1) {
// If we're scrolling down, account for the height of the
// handle in our pixel stop value so that we stop as soon
// as the *bottom* of the handle reaches our click point
pixelStopValue -= handle.getHeight();
}
realStopValue = (int) (pixelStopValue / getValueScale());
}
// Start the automatic scroller
automaticScroller.start(direction, Mouse.ScrollType.BLOCK, realStopValue);
consumed = true;
}
return consumed;
}