mirror of
https://github.com/JetSetIlly/Gopher2600.git
synced 2025-04-02 11:02:17 -04:00
249e3c4b60
the thumbnailer does the actual emulation in a new goroutine so there's no lag here but it's necessary to PushRawEvent() so that rewind.GetState() doesn't race
64 lines
3.5 KiB
Go
64 lines
3.5 KiB
Go
// This file is part of Gopher2600.
|
|
//
|
|
// Gopher2600 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.
|
|
//
|
|
// Gopher2600 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 Gopher2600. If not, see <https://www.gnu.org/licenses/>.
|
|
|
|
// Package rewind coordinates the periodic snapshotting of the emulation state.
|
|
// A previously seen frame can be returned to with the GotoFrame() function. If the
|
|
// requested frame is not in the history then the nearest frame that is will be
|
|
// used. The GotoLast() function will move the emulation to the last frame,
|
|
// whatever that might be.
|
|
//
|
|
// The frequency at which snapshots are made is definable. Frames that are in
|
|
// between the snapshots can still be plumbed in, the rewind package handling
|
|
// the interleaving by running the emulation for the missing period.
|
|
//
|
|
// In fact, the emulation is run even when the rewind package is set to
|
|
// snapshot every frame (a frequency of one) in order to generate the image
|
|
// data (storing the image data is memory wasteful). For this to work, the
|
|
// Rewind type is initialised with a reference to to the Runner interface.
|
|
// Implementations of the Runner interface should loop until frame, scanline,
|
|
// clock are matched (or the nearest point, depending on use case).
|
|
//
|
|
// Regular emulation loops (ie. not catch-up loop of the Runner interface) must
|
|
// call RecordFrameState() after every CPU instruction to catch frame
|
|
// boundaries as early as possible. The rewind package will take the snapshot
|
|
// when it notices a new frame has started.
|
|
//
|
|
// The RecordExecutionState() function can be called to force a snapshot to be
|
|
// taken at any time. This should probably only ever be used when the emulation
|
|
// is paused. The rewind package will delete an execution snapshot when the
|
|
// next snapshot is taken (meaning that there is only ever one execution state
|
|
// in the history at any one time and that it will be at the end).
|
|
//
|
|
// Snapshots are stored in frame order from the splice point. The splice point
|
|
// will be wherever the snapshot history has been rewound to. For example, in a
|
|
// history of length 100 frames: the emulation has rewound back to frame 50.
|
|
// When the emulation is resumed, snapshots will be added at this point. The
|
|
// previous history of frames 51 to 100 will be lost.
|
|
//
|
|
// Reset and Boundary snapshots are special splice points that only ever occur
|
|
// once and at the beginning of the history. Reset occurs only when the Reset()
|
|
// function is called and is intended to be called whenver the VCS is power
|
|
// cycled (not the reset switch).
|
|
//
|
|
// The Boundary snapshot occurs when history has been cleared for some other
|
|
// reason. This was added to better support PlusROM cartridges and to ensure
|
|
// that network events are not replayed. The rewind package will add the
|
|
// boundary snapshot (to an empty history) automatically whenever the
|
|
// RewindBoundary() function from the attached cartridge returns true.
|
|
//
|
|
// One of the weaknesses of the rewind package currently is the absence of any
|
|
// input replay. This might be particularly noticeable with large snapshot
|
|
// frequencies. Future versions of the package will record and replay input.
|
|
package rewind
|