Axis.php

<?php
	/* Libchart - PHP chart library
	 * Copyright (C) 2005-2008 Jean-Marc Trémeaux (jm.tremeaux at gmail.com)
	 * 
	 * 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 3 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.
	 *
	 * You should have received a copy of the GNU General Public License
	 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
	 * 
	 */
	
	/**
	 * Automatic axis boundaries and ticks calibration
	 *
	 * @author Jean-Marc Trémeaux (jm.tremeaux at gmail.com)
	 */
	class Axis {
		private $min;
		private $max;
		private $guide;
		private $delta;
		private $magnitude;
		private $displayMin;
		private $displayMax;
		private $tics;
	
		/**
		 * Creates a new axis formatter.
		 *
		 * @param integer minimum value on the axis
		 * @param integer maximum value on the axis
		 */
		public function __construct($min, $max) {
			$this->min = $min;
			$this->max = $max;

			$this->guide = 10;
		}

		/**
		 * Computes value between two ticks.
		 */
		public function quantizeTics() {
			// Approximate number of decades, in [1..10[
			$norm = $this->delta / $this->magnitude;

			// Approximate number of tics per decade
			$posns = $this->guide / $norm;

			if ($posns > 20) {
				$tics = 0.05;		// e.g. 0, .05, .10, ...
			} else if ($posns > 10) {
				$tics = 0.2;		// e.g.  0, .1, .2, ...
			} else if ($posns > 5) {
				$tics = 0.4;		// e.g.  0, 0.2, 0.4, ...
			} else if ($posns > 3) {
				$tics = 0.5;		// e.g. 0, 0.5, 1, ...
			} else if ($posns > 2) {
				$tics = 1;		// e.g. 0, 1, 2, ...
			} else if ($posns > 0.25) {
				$tics = 2;		// e.g. 0, 2, 4, 6 
			} else {
				$tics = ceil($norm);
			}
			
			$this->tics = $tics * $this->magnitude;
		}

		/**
		 * Computes automatic boundaries on the axis
		 */
		public function computeBoundaries() {
			// Range
			$this->delta = abs($this->max - $this->min);

			// Check for null distribution
			if ($this->delta == 0)
				$this->delta = 1;
			
			// Order of magnitude of range
			$this->magnitude = pow(10, floor(log10($this->delta)));
			
			$this->quantizeTics();

			$this->displayMin = floor($this->min / $this->tics) * $this->tics;
			$this->displayMax = ceil($this->max / $this->tics) * $this->tics;
			$this->displayDelta = $this->displayMax - $this->displayMin;
		
			// Check for null distribution
			if ($this->displayDelta == 0) {
				$this->displayDelta = 1;
			}
		}

		/**
		 * Get the lower boundary on the axis3
		 *
		 * @return integer lower boundary on the axis
		 */
		public function getLowerBoundary() {
			return $this->displayMin;
		}

		/**
		 * Get the upper boundary on the axis3
		 *
		 * @return integer upper boundary on the axis
		 */
		public function getUpperBoundary() {
			return $this->displayMax;
		}

		/**
		 * Get the value between two ticks3
		 *
		 * @return integer value between two ticks
		 */
		public function getTics() {
			return $this->tics;
		}
	}
?>