scrollbar.java

Bluetooth chat Server and Client in j2me

/*
 I BlueTooth You -- Simple BlueTooth talker
 Copyright (C) 2007 Jan Tomka

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 as published by the Free Software Foundation; either version 2
 of the License, or (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 */
package net.sf.btw.ibtu.ui;

import javax.microedition.lcdui.Graphics;

/**
 * This class defines a simple vertical scrollbar. It is a graphics entity to be
 * displayed on {@link Graphics}. It visually represents the position and
 * height of currently displayed portion relative to the actual height of
 * another graphics entity being scrolled.
 * 
 * @author Jan Tomka
 *
 * TODO Scrollbar should only paint its thumb, painting the frame should be
 * left to the owner.
 */
public class Scrollbar {
	/**
	 * Horizontal X-coordinate of a scrollbar.
	 */
	private final int x;

	/**
	 * Zero-based vertical Y-coordinate of a scrollbar.
	 */
	private final int y;

	/**
	 * Horizontal width of a scrollbar.
	 */
	private final int width;

	/**
	 * Vertical height of a scrollbar.
	 */
	private final int height;

	/**
	 * Refrence to the object whose scrolling properties Scrollbar is notified
	 * about.
	 */
	private IScrollNotifier notifier;

	/**
	 * Creates new Scrollbar object with given position and dimensions.
	 * 
	 * @param x
	 *            Initial horizontal X-coordinate of a scrollbar.
	 * @param y
	 *            Initial vertical Y-coordinate of a scrollbar.
	 * @param width
	 *            Initial horizontal width of a scrollbar.
	 * @param height
	 *            Initial vertical height of a scrollbar.
	 */
	public Scrollbar(int x, int y, int width, int height) {
		this.x = x;
		this.y = y;
		this.width = width;
		this.height = height;
	}

	/**
	 * Returns the zero-based horizontal X-coordinate of a scrollbar within the
	 * parent {@link Graphics}.
	 * 
	 * @return The X-coordinate of a scrollbar.
	 */
	public int getX() {
		return x;
	}

	/**
	 * Returns the zero-based vertical Y-coordinate of a scrollbar within the
	 * parent {@link Graphics}.
	 * 
	 * @return The Y-coordinate of a scrollbar.
	 */
	public int getY() {
		return y;
	}

	/**
	 * Returns the horizontal width of a scrollbar.
	 * 
	 * @return Width of scrollbar.
	 */
	public int getWidth() {
		return width;
	}

	/**
	 * Returns the vertical height of a scrollbar.
	 * 
	 * @return Height of scrollbar.
	 */
	public int getHeight() {
		return height;
	}

	/**
	 * Saves reference to {@link IScrollNotifier} object, whose current
	 * scrolling-related properties will be notified to the Scrollbar.
	 * 
	 * @param sn
	 *            Reference to scroll notifier. If <code>null</code>,
	 *            existing notifier is removed.
	 */
	public void setIScrollNotifier(IScrollNotifier sn) {
		notifier = sn;
	}

	/**
	 * Paints the scrollbar. Draws a rectangle given by {@link Scrollbar#getX()},
	 * {@link Scrollbar#getY()}, {@link Scrollbar#getWidth()} and
	 * {@link Scrollbar#getHeight()}. Scrollbar thumb is then drawn so that it
	 * represents the position and height of currently visible portion, relative
	 * to the height of the entire area being scrolled.
	 * 
	 * @param g
	 *            {@link Graphics} to draw Scrollbar on.
	 */
	// TODO Optimize repainting process.
	public void paint(Graphics g) {
		if (notifier == null)
			return;

		int visLen = notifier.getVisibleLength();
		int actLen = notifier.getActualLength();
		int curPos = notifier.getCurrentPosition();

		int thumbHeight;
		if (actLen == 0)
			thumbHeight = height - 3;
		else {
			thumbHeight = ((1000 * height) / actLen * visLen) / 1000;
			if (thumbHeight < 1)
				thumbHeight = 1;
			else if (thumbHeight > height - 3)
				thumbHeight = height - 3;
		}

		int thumbY;
		if (curPos == 0)
			thumbY = y + 2;
		else {
			if ((actLen <= visLen) || curPos >= (actLen - visLen))
				// Adjust curPos within the last screen
				thumbY = y + height - 1 - thumbHeight;
			else
				thumbY = y + 1 + ((1000 * height) / actLen * curPos) / 1000;
			if (thumbY < y + 2)
				thumbY = y + 2;
		}

		g.drawRect(x, y, width, height);
		g.fillRect(x + 2, thumbY, width - 3, thumbHeight);
	}
}