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84 lines
3.9 KiB
Go
84 lines
3.9 KiB
Go
// This file is part of Gopher2600.
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//
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// Gopher2600 is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// Gopher2600 is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with Gopher2600. If not, see <https://www.gnu.org/licenses/>.
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// Package television implements the output device of the emulated VCS.
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//
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// It is possible for instances of television to be embedded in other type
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// structure, thereby extending the "features" of the television and allowing
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// the extended type to be used wherever the Television interface is required.
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// The digest package is a good example of this idea.
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//
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// It is important to note that the television package does not render pixels
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// or mix sound. Instead, the television interface exposes two functions,
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// AddPixelRenderer() and AddAudioMixer(). These can be used to add as many
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// renderers and mixers as required.
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//
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// For audio outputs that are time sensitive, the AddRealtimeAudioMixer()
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// function should be used. This requires a slightly different implementation
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// (see RealtimeAudioMixer interface) and only one such implemenation can be
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// registered at any one time.
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//
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// There is also the FrameTrigger and PauseTrigger interfaces for applications
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// that have limited need for a full pixel renderer.
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//
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// The main means of communication is the Signal() function. This function
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// accepts an instance of SignalAttributes which gives details of how the
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// television should be behaving.
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//
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// Note that the television implementation no longer attempts to report the
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// same frame/scanline/clock information as Stella. Early versions of the
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// implementation did because it facilitated A/B testing but since we're
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// now confident that the TIA emulation is correct the need to keep in "sync"
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// with Stella is no longer required.
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//
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// The reference implementation also handles framerate limiting according to
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// the current incoming TV signal. For debugging purposes, the framerate can
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// also be set to a specific value
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//
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// Framesize adaptation is also handled by the television package. Current
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// information about the frame can be acquired with GetFrameInfo(). FrameInfo
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// will also be sent to the PixelRenderers as appropriate.
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//
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// # Screen Rolling
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//
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// Screen rolling is not handled by the television package. However, the synced
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// argument of the NewFrame() function in the PixelRenderer and FrameTrigger
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// interfaces can be used to implement it if required. Something like this:
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//
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// 1. If Synced is false, note scanline of last plot (unsynedScanline)
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// 2. For every SetPixel() add unsyncedScanline to the Scanline value in
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// the SignalAttributes struct (adjustedScanline)
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// 3. Bring adjustedScanline into range by modulo ScanlinesTotal of the
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// current TV specification.
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//
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// Recovery from a screen roll should also be emulated. A good way of doing
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// this is to reduce unsyncedScanline by a percentage (80% say) on synced
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// frames (or every other synced frame) after an unsynced frame.
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//
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// A good additionl policy would be to only roll if several, consecutive
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// unsynced frames are indicated.
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//
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// # Concurrency
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//
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// None of the functions in the Television type are safe to be called from
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// goroutines other than the one the type was created in.
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//
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// # Logging
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//
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// The television does no logging. This is because the television can be used
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// ephemerally and logging would be noisy. Callers of television package
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// functions should decide whether it is appropriate to log.
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package television
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