lightpen.h

/*
 * This file is part of libsidplayfp, a SID player engine.
 *
 * Copyright 2011-2021 Leandro Nini <drfiemost@users.sourceforge.net>
 * Copyright 2009-2014 VICE Project
 * Copyright 2007-2010 Antti Lankila
 * Copyright 2001 Simon White
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */
 
#ifndef LIGHTPEN_H
#define LIGHTPEN_H
 
namespace libsidplayfp
{
 
class Lightpen
{
private:
    unsigned int lastLine;
 
    unsigned int cyclesPerLine;
 
    unsigned int lpx;
 
    unsigned int lpy;
 
    bool isTriggered;
 
private:
    uint8_t getXpos(unsigned int lineCycle) const
    {
        if (lineCycle < 13)
            lineCycle += cyclesPerLine;
 
        lineCycle -= 13;
 
        // On NTSC the xpos is not incremented at lineCycle 61
        if ((cyclesPerLine == 65) && (lineCycle > (61 - 13)))
        {
            lineCycle--;
        }
 
        return lineCycle << 2;
    }
 
public:
    void setScreenSize(unsigned int height, unsigned int width)
    {
        lastLine = height - 1;
        cyclesPerLine = width;
    }
 
    void reset()
    {
        lpx = 0;
        lpy = 0;
        isTriggered = false;
    }
 
    uint8_t getX() const { return lpx; }
 
    uint8_t getY() const { return lpy; }
 
    bool retrigger()
    {
        if (isTriggered)
            return false;
 
        isTriggered = true;
 
        switch (cyclesPerLine)
        {
        case 63:
        default:
            lpx = 0xd1;
            break;
        case 65:
            lpx = 0xd5;
            break;
        }
 
        lpy = 0;
 
        return true;
    }
 
    bool trigger(unsigned int lineCycle, unsigned int rasterY)
    {
        if (isTriggered)
            return false;
 
        isTriggered = true;
 
        // don't latch on the last line, except on the first cycle
        if ((rasterY == lastLine) && (lineCycle > 0))
        {
            return false;
        }
 
        // Latch current coordinates
        lpx = getXpos(lineCycle) + 2; // + 1 for MOS 85XX
        lpy = rasterY;
 
        // On 6569R1 and 6567R56A the interrupt is triggered only
        // when the line is low on the first cycle of the frame.
        return true; // false for old chip revisions
    }
 
    void untrigger() { isTriggered = false; }
};
 
}
 
#endif