Trackball.cc

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#include "Trackball.hh"
#include "MSXEventDistributor.hh"
#include "StateChangeDistributor.hh"
#include "Event.hh"
#include "StateChange.hh"
#include "narrow.hh"
#include "serialize.hh"
#include "serialize_meta.hh"
#include <algorithm>
 
// * Implementation based on information we received from 'n_n'.
//   It might not be 100% accurate. But games like 'Hole in one' already work.
// * Initially the 'trackball detection' code didn't work properly in openMSX
//   while it did work in meisei. Meisei had some special cases implemented for
//   the first read after reset. After some investigation I figured out some
//   code without special cases that also works as expected. Most software
//   seems to work now, though the detailed behaviour is still not tested
//   against the real hardware.
 
namespace openmsx {
 
class TrackballState final : public StateChange
{
public:
        TrackballState() = default; // for serialize
        TrackballState(EmuTime::param time_, int deltaX_, int deltaY_,
                                             uint8_t press_, uint8_t release_)
                : StateChange(time_)
                , deltaX(deltaX_), deltaY(deltaY_)
                , press(press_), release(release_) {}
        [[nodiscard]] int     getDeltaX()  const { return deltaX; }
        [[nodiscard]] int     getDeltaY()  const { return deltaY; }
        [[nodiscard]] uint8_t getPress()   const { return press; }
        [[nodiscard]] uint8_t getRelease() const { return release; }
 
        template<typename Archive> void serialize(Archive& ar, unsigned /*version*/)
        {
                ar.template serializeBase<StateChange>(*this);
                ar.serialize("deltaX",  deltaX,
                             "deltaY",  deltaY,
                             "press",   press,
                             "release", release);
        }
private:
        int deltaX, deltaY;
        uint8_t press, release;
};
REGISTER_POLYMORPHIC_CLASS(StateChange, TrackballState, "TrackballState");
 
 
Trackball::Trackball(MSXEventDistributor& eventDistributor_,
                     StateChangeDistributor& stateChangeDistributor_)
        : eventDistributor(eventDistributor_)
        , stateChangeDistributor(stateChangeDistributor_)
{
}
 
Trackball::~Trackball()
{
        if (isPluggedIn()) {
                Trackball::unplugHelper(EmuTime::dummy());
        }
}
 
 
// Pluggable
std::string_view Trackball::getName() const
{
        return "trackball";
}
 
std::string_view Trackball::getDescription() const
{
        return "MSX Trackball";
}
 
void Trackball::plugHelper(Connector& /*connector*/, EmuTime::param time)
{
        eventDistributor.registerEventListener(*this);
        stateChangeDistributor.registerListener(*this);
        lastSync = time;
        targetDeltaX = 0;
        targetDeltaY = 0;
        currentDeltaX = 0;
        currentDeltaY = 0;
}
 
void Trackball::unplugHelper(EmuTime::param /*time*/)
{
        stateChangeDistributor.unregisterListener(*this);
        eventDistributor.unregisterEventListener(*this);
}
 
// JoystickDevice
uint8_t Trackball::read(EmuTime::param time)
{
        // From the Sony GB-7 Service manual:
        //  http://cdn.preterhuman.net/texts/computing/msx/sonygb7sm.pdf
        // * The counter seems to be 8-bit wide, though only 4 bits (bit 7 and
        //   2-0) are connected to the MSX. Looking at the M60226 block diagram
        //   in more detail shows that the (up/down-)counters have a 'HP'
        //   input, in the GB7 this input is hardwired to GND. My *guess* is
        //   that HP stands for either 'Half-' or 'High-precision' and that it
        //   selects between either 4 or 8 bits saturation.
        //   The bug report '#477 Trackball emulation overflow values too
        //   easily' contains a small movie. Some very rough calculations
        //   indicate that when you move a cursor 50 times per second, 8 pixels
        //   per step, you get about the same speed as in that move.
        //   So even though both 4 and 8 bit clipping *seem* to be possible,
        //   this code only implements 4 bit clipping.
        // * It also contains a test program to read the trackball position.
        //   This program first reads the (X or Y) value and only then toggles
        //   pin 8. This seems to suggest the actual (X or Y) value is always
        //   present on reads and toggling pin 8 resets this value and switches
        //   to the other axis.
        syncCurrentWithTarget(time);
        auto delta = (lastValue & 4) ? currentDeltaY : currentDeltaX;
        return (status & ~0x0F) | ((delta + 8) & 0x0F);
}
 
void Trackball::write(uint8_t value, EmuTime::param time)
{
        syncCurrentWithTarget(time);
        uint8_t diff = lastValue ^ value;
        lastValue = value;
        if (diff & 0x4) {
                // pin 8 flipped
                if (value & 4) {
                        targetDeltaX = narrow<int8_t>(std::clamp(targetDeltaX - currentDeltaX, -8, 7));
                        currentDeltaX = 0;
                } else {
                        targetDeltaY = narrow<int8_t>(std::clamp(targetDeltaY - currentDeltaY, -8, 7));
                        currentDeltaY = 0;
                }
        }
}
 
void Trackball::syncCurrentWithTarget(EmuTime::param time)
{
        // In the past we only had 'targetDeltaXY' (was named 'deltaXY' then).
        // 'currentDeltaXY' was introduced to (slightly) smooth-out the
        // discrete host mouse movement events over time. This method performs
        // that smoothing calculation.
        //
        // In emulation, the trackball movement is driven by host mouse
        // movement events. These events are discrete. So for example if we
        // receive a host mouse event with offset (3,-4) we immediately adjust
        // 'targetDeltaXY' by that offset. However in reality mouse movement
        // doesn't make such discrete jumps. If you look at small enough time
        // intervals you'll see that the offset smoothly varies from (0,0) to
        // (3,-4).
        //
        // Most often this discretization step doesn't matter. However the BIOS
        // routine GTPAD to read mouse/trackball (more specifically PAD(12) and
        // PAD(16) has an heuristic to distinguish the mouse from the trackball
        // protocol. I won't go into detail, but in short it's reading the
        // mouse/trackball two times shortly after each other and checks
        // whether the offset of the 2nd read is centered around 0 (for mouse)
        // or 8 (for trackball). There's only about 1 millisecond between the
        // two reads, so in reality the mouse/trackball won't have moved much
        // during that time. However in emulation because of the discretization
        // we can get unlucky and do see a large offset for the 2nd read. This
        // confuses the BIOS (it thinks it's talking to a mouse instead of
        // trackball) and it results in erratic trackball movement.
        //
        // Thus to work around this problem (=make the heuristic in the BIOS
        // work) we smear-out host mouse events over (emulated) time. Instead
        // of immediately following the host movement, we limit changes in the
        // emulated offsets to a rate of 1 step per millisecond. This
        // introduces some delay, but usually (for not too fast movements) it's
        // not noticeable.
 
        if (!smooth) {
                // for backwards-compatible replay files
                currentDeltaX = targetDeltaX;
                currentDeltaY = targetDeltaY;
                return;
        }
 
        static constexpr auto INTERVAL = EmuDuration::msec(1);
 
        auto maxSteps = narrow<int>((time - lastSync) / INTERVAL);
        lastSync += INTERVAL * maxSteps;
 
        if (targetDeltaX >= currentDeltaX) {
                currentDeltaX = narrow<int8_t>(std::min<int>(currentDeltaX + maxSteps, targetDeltaX));
        } else {
                currentDeltaX = narrow<int8_t>(std::max<int>(currentDeltaX - maxSteps, targetDeltaX));
        }
        if (targetDeltaY >= currentDeltaY) {
                currentDeltaY = narrow<int8_t>(std::min<int>(currentDeltaY + maxSteps, targetDeltaY));
        } else {
                currentDeltaY = narrow<int8_t>(std::max<int>(currentDeltaY - maxSteps, targetDeltaY));
        }
}
 
// MSXEventListener
void Trackball::signalMSXEvent(const Event& event,
                               EmuTime::param time) noexcept
{
        visit(overloaded{
                [&](const MouseMotionEvent& e) {
                        constexpr int SCALE = 2;
                        int dx = e.getX() / SCALE;
                        int dy = e.getY() / SCALE;
                        if ((dx != 0) || (dy != 0)) {
                                createTrackballStateChange(time, dx, dy, 0, 0);
                        }
                },
                [&](const MouseButtonDownEvent& e) {
                        switch (e.getButton()) {
                        case SDL_BUTTON_LEFT:
                                createTrackballStateChange(time, 0, 0, JOY_BUTTONA, 0);
                                break;
                        case SDL_BUTTON_RIGHT:
                                createTrackballStateChange(time, 0, 0, JOY_BUTTONB, 0);
                                break;
                        default:
                                // ignore other buttons
                                break;
                        }
                },
                [&](const MouseButtonUpEvent& e) {
                        switch (e.getButton()) {
                        case SDL_BUTTON_LEFT:
                                createTrackballStateChange(time, 0, 0, 0, JOY_BUTTONA);
                                break;
                        case SDL_BUTTON_RIGHT:
                                createTrackballStateChange(time, 0, 0, 0, JOY_BUTTONB);
                                break;
                        default:
                                // ignore other buttons
                                break;
                        }
                },
                [](const EventBase&) { /*ignore*/ }
        }, event);
}
 
void Trackball::createTrackballStateChange(
        EmuTime::param time, int deltaX, int deltaY, uint8_t press, uint8_t release)
{
        stateChangeDistributor.distributeNew<TrackballState>(
                time, deltaX, deltaY, press, release);
}
 
// StateChangeListener
void Trackball::signalStateChange(const StateChange& event)
{
        const auto* ts = dynamic_cast<const TrackballState*>(&event);
        if (!ts) return;
 
        targetDeltaX = narrow<int8_t>(std::clamp(targetDeltaX + ts->getDeltaX(), -8, 7));
        targetDeltaY = narrow<int8_t>(std::clamp(targetDeltaY + ts->getDeltaY(), -8, 7));
        status = (status & ~ts->getPress()) | ts->getRelease();
}
 
void Trackball::stopReplay(EmuTime::param time) noexcept
{
        syncCurrentWithTarget(time);
        // TODO Get actual mouse button(s) state. Is it worth the trouble?
        uint8_t release = (JOY_BUTTONA | JOY_BUTTONB) & ~status;
        if ((currentDeltaX != 0) || (currentDeltaY != 0) || (release != 0)) {
                stateChangeDistributor.distributeNew<TrackballState>(
                        time, -currentDeltaX, -currentDeltaY, uint8_t(0), release);
        }
}
 
// version 1: initial version
// version 2: replaced deltaXY with targetDeltaXY and currentDeltaXY
template<typename Archive>
void Trackball::serialize(Archive& ar, unsigned version)
{
        if (ar.versionAtLeast(version, 2)) {
                ar.serialize("lastSync",      lastSync,
                             "targetDeltaX",  targetDeltaX,
                             "targetDeltaY",  targetDeltaY,
                             "currentDeltaX", currentDeltaX,
                             "currentDeltaY", currentDeltaY);
        } else {
                ar.serialize("deltaX", targetDeltaX,
                             "deltaY", targetDeltaY);
                currentDeltaX = targetDeltaX;
                currentDeltaY = targetDeltaY;
                smooth = false;
        }
        ar.serialize("lastValue", lastValue,
                     "status",    status);
 
        if constexpr (Archive::IS_LOADER) {
                if (isPluggedIn()) {
                        plugHelper(*getConnector(), EmuTime::dummy());
                }
        }
}
INSTANTIATE_SERIALIZE_METHODS(Trackball);
REGISTER_POLYMORPHIC_INITIALIZER(Pluggable, Trackball, "Trackball");
 
} // namespace openmsx