voluntarywavegenerator.java

一个用java写成的gb模拟器的源代码。

/*

JavaBoy
                                  
COPYRIGHT (C) 2001 Neil Millstone and The Victoria University of Manchester
                                                                         ;;;
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.


You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA.

*/

class VoluntaryWaveGenerator {
	public static final int CHAN_LEFT = 1;
	public static final int CHAN_RIGHT = 2;
	public static final int CHAN_MONO = 4;

	int totalLength;
	int cyclePos;
	int cycleLength;
	int amplitude;
	int channel;
	int sampleRate;
	int volumeShift;

	byte[] waveform = new byte[32];

	public VoluntaryWaveGenerator(
		int waveLength,
		int ampl,
		int duty,
		int chan,
		int rate) {
		cycleLength = waveLength;
		amplitude = ampl;
		cyclePos = 0;
		channel = chan;
		sampleRate = rate;
	}

	public VoluntaryWaveGenerator(int rate) {
		cyclePos = 0;
		channel = CHAN_LEFT | CHAN_RIGHT;
		cycleLength = 2;
		totalLength = 0;
		sampleRate = rate;
		amplitude = 32;
	}

	public void setSampleRate(int sr) {
		sampleRate = sr;
	}

	public void setFrequency(int gbFrequency) {
		//  cyclePos = 0;
		float frequency = (int) ((float) 65536 / (float) (2048 - gbFrequency));
		//  System.out.println("gbFrequency: " + gbFrequency + "");
		cycleLength = (int) ((float) (256f * sampleRate) / (float) frequency);
		if (cycleLength == 0)
			cycleLength = 1;
		//  System.out.println("Cycle length : " + cycleLength + " samples");
	}

	public void setChannel(int chan) {
		channel = chan;
	}
	
	public int getLength() {
		return totalLength;
	}

	public void setLength(int gbLength) {
		if (gbLength == -1) {
			totalLength = -1;
		} else {
			totalLength = (256 - gbLength) / 4;
		}
	}

	public void setSamplePair(int address, int value) {
		waveform[address * 2] = (byte) ((value & 0xF0) >> 4);
		waveform[address * 2 + 1] = (byte) ((value & 0x0F));
	}

	public void setVolume(int volume) {
		switch (volume) {
			case 0 :
				volumeShift = 5;
				break;
			case 1 :
				volumeShift = 0;
				break;
			case 2 :
				volumeShift = 1;
				break;
			case 3 :
				volumeShift = 2;
				break;
		}
		//  System.out.println("A:"+volume);
	}

	public void play(byte[] b, int length, int offset) {
		int val;

		if (totalLength != 0) {
			totalLength--;

			for (int r = offset; r < offset + length; r++) {

				int samplePos = (31 * cyclePos) / cycleLength;
				val =
					((waveform[samplePos & 31]) & 0xff)
						>> volumeShift
						<< 1;
				//    System.out.print(" " + val);

				if ((channel & CHAN_LEFT) != 0)
					b[r * 2] += val;
				if ((channel & CHAN_RIGHT) != 0)
					b[r * 2 + 1] += val;
				if ((channel & CHAN_MONO) != 0)
					b[r] += val;

				//   System.out.print(val + " ");
				cyclePos = (cyclePos + 256) % cycleLength;
			}
		}
	}

}