television

package
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 Go to latest Published: May 30, 2022 License: GPL-3.0, GPL-3.0 Imports: 10 Imported by: 3

Documentation

Overview

Package television implements the output device of the emulated VCS.

It is possible for instances of television to be embedded in other type structure, thereby extending the "features" of the television and allowing the extended type to be used wherever the Television interface is required. The digest package is a good example of this idea.

It is important to note that the television package does not render pixels or mix sound. Instead, the television interface exposes two functions, AddPixelRenderer() and AddAudioMixer(). These can be used to add as many renderers and mixers as required.

For audio outputs that are time sensitive, the AddRealtimeAudioMixer() function should be used. This requires a slightly different implementation (see RealtimeAudioMixer interface) and only one such implemenation can be registered at any one time.

There is also the FrameTrigger and PauseTrigger interfaces for applications that have limited need for a full pixel renderer.

The main means of communication is the Signal() function. This function accepts an instance of SignalAttributes which gives details of how the television should be behaving.

Note that the television implementation no longer attempts to report the same frame/scanline/clock information as Stella. Early versions of the implementation did because it facilitated A/B testing but since we're now confident that the TIA emulation is correct the need to keep in "sync" with Stella is no longer required.

The reference implementation also handles framerate limiting according to the current incoming TV signal. For debugging purposes, the framerate can also be set to a specific value

Framesize adaptation is also handled by the television package. Current information about the frame can be acquired with GetFrameInfo(). FrameInfo will also be sent to the PixelRenderers as appropriate.

Screen Rolling

Screen rolling is not handled by the television package. However, the synced argument of the NewFrame() function in the PixelRenderer and FrameTrigger interfaces can be used to implement it if required. Something like this:

  1. If Synced is false, note scanline of last plot (unsynedScanline)
  2. For every SetPixel() add unsyncedScanline to the Scanline value in the SignalAttributes struct (adjustedScanline)
  3. Bring adjustedScanline into range by modulo ScanlinesTotal of the current TV specification.

Recovery from a screen roll should also be emulated. A good way of doing this is to reduce unsyncedScanline by a percentage (80% say) on synced frames (or every other synced frame) after an unsynced frame.

A good additionl policy would be to only roll if several, consecutive unsynced frames are indicated.

Concurrency

None of the functions in the Television type are safe to be called from goroutines other than the one the type was created in.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

This section is empty.

Types

type Adj added in v0.15.0 

type Adj int

Adj is used to specify adjustment scale for the ReqAdjust() function. 

const (
	AdjFrame Adj = iota
	AdjScanline
	AdjCPUCycle
	AdjClock
)

List of valid Adj values.

type AudioMixer 

type AudioMixer interface {
	// for efficiency reasons, SetAudio() implementations can be sent
	// SignalAttributes values that do not have valid AudioData (ie.
	// AudioUpdate bit is zero). implemenations should therefore take care when
	// processing the sig slice.
	//
	// the general algorithm for processing the sig slice is:
	//
	//	for _, s := range sig {
	//		if s&signal.AudioUpdate != signal.AudioUpdate {
	//			continue
	//		}
	//		d := uint8((s & signal.AudioData) >> signal.AudioDataShift)
	//
	//		...
	//	}
	SetAudio(sig []signal.SignalAttributes) error

	// some mixers may need to conclude and/or dispose of resources gently.
	// for simplicity, the AudioMixer should be considered unusable after
	// EndMixing() has been called
	EndMixing() error

	// Reset buffered audio and anything else that might need doing on, for
	// example, a cartridge change.
	Reset()
}

AudioMixer implementations work with sound; most probably playing it. An example of an AudioMixer that does not play sound but otherwise works with it is the digest.Audio type.

type FrameInfo added in v0.14.0 

type FrameInfo struct {
	Spec specification.Spec

	FrameNum int

	VisibleTop    int
	VisibleBottom int

	TotalScanlines int

	// the refresh rate. calculated from the TotalScanlines value
	RefreshRate float32

	// a VSynced frame is one which was generated from a valid VSYNC/VBLANK
	// sequence and which hasn't cause the update frequency of the television
	// to change.
	VSynced bool

	// Stable is true once the television frame has been consistent for N frames
	// after reset. This is useful for pixel renderers so that they don't show
	// the loose frames that often occur after VCS reset.
	//
	// once Stable is true then the Specification will not change (except
	// manually). This is important for ROMs that allow the VCS to run without
	// VSYNC - we don't want those ROMs to change the specifciation after he
	// startup period. A good example of such a ROM is Andrew Davie's 3e+ chess
	// demos.
	Stable bool
}

FrameInfo records the current frame information, as opposed to the optimal values of the specification, a copy of which is provided as reference.

func NewFrameInfo added in v0.14.0 

func NewFrameInfo(spec specification.Spec) FrameInfo

NewFrameInfo returns an initialised FrameInfo for the specification.

func (FrameInfo) IsAtariSafe added in v0.14.0 

func (info FrameInfo) IsAtariSafe() bool

IsAtariSafe returns true if the current frame matches the AtariSafe values of the current specification.

func (FrameInfo) String added in v0.14.0 

func (info FrameInfo) String() string

func (FrameInfo) TotalClocks added in v0.18.0 

func (info FrameInfo) TotalClocks() int

TotalClocks returns the total number of clocks required to generate the frame. The value returned assumes scanlines are complete - which may not be the case.

type FrameTrigger 

type FrameTrigger interface {
	// See NewFrame() comment for PixelRenderer interface.
	NewFrame(FrameInfo) error
}

FrameTrigger implementations listen for NewFrame events. FrameTrigger is a subset of PixelRenderer.

type PauseTrigger added in v0.10.1 

type PauseTrigger interface {
	Pause(pause bool) error
}

FrameTrigger implementations listen for Pause events.

type PixelRenderer 

type PixelRenderer interface {
	// Resize is called when the television implementation detects that extra
	// scanlines are required in the display.
	//
	// Renderers must be prepared to resize to either a smaller or larger size.
	//
	// Resize can also be called speculatively so implementations should take
	// care not to perform any resizing unless absolutely necessary.
	//
	// The VisibleTop and VisibleBottom fields in the FrameInfor argument,
	// describe the top and bottom scanline that is *visible* on a normal
	// screen. pixels outside this range that are sent by SetPixel() can be
	// handled according to the renderers needs but would not normally be shown
	// for game-playing purposes.
	Resize(FrameInfo) error

	// NewFrame is called at the start of a new fame.
	NewFrame(FrameInfo) error

	// NewScanline is called at the start of a new scanline
	NewScanline(scanline int) error

	// SetPixels is used to Render a series of signals. The number of signals
	// will always be television.MaxSignalHistory.
	//
	// Producing a 2d image from the signals sent by SetPixels() can easily be
	// done by first allocating a bitmap of width specification.ClksScanline
	// and height specification.AbsoluateMaxScanlines. This bitmap will have
	// television.MaxSignalHistory entries.
	//
	// Every signal from SetPixels() therefore corresponds to a pixel in the
	// bitmap - the first entry always referes to the top-left pixel.
	//
	// Setting the color of a pixel can be done by extracting the ColorSignal
	// from the SignalAttributes (see signal package)
	//
	// The last parameter indicates the index of the array entry that was most
	// recently set. This is useful to know when showing televison images when
	// the emulation is paused. All entries upto and including last are from
	// teh *current* frame. All entries afterwards are from the *previous*
	// frame.
	//
	// If the entry contains signal.NoSignal then that screen pixel has not
	// been written to recently.
	//
	// For renderers that are producing an accurate visual image, the pixel
	// should always be set to video black if VBLANK is on. Some renderers
	// however may find it useful to set the pixel to the RGB value regardless
	// of VBLANK.
	//
	// A very important note is that some ROMs use VBLANK to control pixel
	// color within the visible display area. For example:
	//
	//	* Custer's Revenge
	//	* Ladybug
	//	* ET (turns VBLANK off late on scanline 40)
	//
	// In other words, the PixelRenderer should not simply assume VBLANK is
	// restricted to the "off-screen" areas as defined by the FrameInfo sent to
	// Resize()
	SetPixels(sig []signal.SignalAttributes, last int) error

	// Reset all pixels. Called when TV is reset.
	//
	// Note that a Reset event does not imply a Resize() event. Implementations
	// should not call the Resize() function as a byproduct of a Reset(). The
	// television will send an explicit Resize() request if it is appropriate.
	Reset()

	// Some renderers may need to conclude and/or dispose of resources gently.
	EndRendering() error
}

PixelRenderer implementations displays, or otherwise works with, visual information from a television. For example digest.Video.

PixelRenderer implementations often find it convenient to maintain a reference to the parent Television implementation and maybe even embed the Television interface. ie. 

type ExampleTV struct {
	television.Television
	...
}

The most useful source of information though is the FrameInfo type supplied to the PixelRenderer through the Resize() and NewFrame() functions. A current copy of this information is also available from the television type GetFrameInfo() function.

type RealtimeAudioMixer added in v0.15.0 

type RealtimeAudioMixer interface {
	AudioMixer
	MoreAudio() bool
}

RealtimeAudioMixer is an extension for the AudioMixer interface. Implementations of this interface expect to be given more audio data on demand.

MoreAudio() is called periodically (every scanline) and the implementation should return true if more audio data is required immediately.

type State 

type State struct {
	// contains filtered or unexported fields
}

State encapsulates the television values that can change from moment to moment. Used by the rewind system when recording the current television state.

func (*State) GetCoords added in v0.15.0 

func (s *State) GetCoords() coords.TelevisionCoords

GetCoords returns an instance of coords.TelevisionCoords.

func (*State) Snapshot 

func (s *State) Snapshot() *State

Snapshot makes a copy of the television state.

func (*State) String added in v0.10.1 

func (s *State) String() string

type Television 

type Television struct {
	// contains filtered or unexported fields
}

Television is a Television implementation of the Television interface. In all honesty, it's most likely the only implementation required.

func NewTelevision 

func NewTelevision(spec string) (*Television, error)

NewReference creates a new instance of the reference television type, satisfying the Television interface.

func (*Television) AddAudioMixer 

func (tv *Television) AddAudioMixer(m AudioMixer)

AddAudioMixer adds an implementation of AudioMixer.

func (*Television) AddFrameTrigger 

func (tv *Television) AddFrameTrigger(f FrameTrigger)

AddFrameTrigger adds an implementation of FrameTrigger.

func (*Television) AddPixelRenderer 

func (tv *Television) AddPixelRenderer(r PixelRenderer)

AddPixelRenderer adds an implementation of PixelRenderer.

func (*Television) AddRealtimeAudioMixer added in v0.15.0 

func (tv *Television) AddRealtimeAudioMixer(m RealtimeAudioMixer)

AddRealtimeAudioMixer adds a RealtimeAudioMixer. Any previous assignment is lost.

func (*Television) AdjCoords added in v0.15.0 

func (tv *Television) AdjCoords(adj Adj, amount int) coords.TelevisionCoords

AdjCoords returns a coords.TelevisionCoords with the current coords adjusted by the specified amount.

func (*Television) AttachVCS added in v0.8.0 

func (tv *Television) AttachVCS(vcs VCSReturnChannel)

AttachVCS attaches an implementation of the VCSReturnChannel.

func (*Television) End 

func (tv *Television) End() error

some televisions may need to conclude and/or dispose of resources gently. implementations of End() should call EndRendering() and EndMixing() on each PixelRenderer and AudioMixer that has been added.

for simplicity, the Television should be considered unusable after EndRendering() has been called.

func (*Television) GetActualFPS 

func (tv *Television) GetActualFPS() (float32, float32)

GetActualFPS returns the current number of frames per second and the detected frequency of the TV signal.

Note that FPS measurement still works even when frame capping is disabled.

IS goroutine safe.

func (*Television) GetCoords added in v0.15.0 

func (tv *Television) GetCoords() coords.TelevisionCoords

GetCoords returns an instance of coords.TelevisionCoords.

Like all Television functions this function is not safe to call from goroutines other than the one that created the Television.

func (*Television) GetFrameInfo added in v0.14.0 

func (tv *Television) GetFrameInfo() FrameInfo

GetFrameInfo returns the television's current frame information.

func (*Television) GetLastSignal 

func (tv *Television) GetLastSignal() signal.SignalAttributes

GetLastSignal returns a copy of the most SignalAttributes sent to the TV (via the Signal() function).

func (*Television) GetReqFPS 

func (tv *Television) GetReqFPS() float32

GetReqFPS returns the requested number of frames per second. Compare with GetActualFPS() to check for accuracy.

IS goroutine safe.

func (*Television) GetReqSpecID 

func (tv *Television) GetReqSpecID() string

GetReqSpecID returns the specification that was requested on creation.

func (*Television) PlumbState added in v0.8.0 

func (tv *Television) PlumbState(vcs VCSReturnChannel, s *State)

PlumbState attaches an existing television state.

func (*Television) RemoveAudioMixer added in v0.16.0 

func (tv *Television) RemoveAudioMixer(m AudioMixer)

RemoveAudioMixer removes a single AudioMixer implementation from the list of mixers. Order is not maintained.

func (*Television) RemoveFrameTrigger added in v0.16.0 

func (tv *Television) RemoveFrameTrigger(f FrameTrigger)

RemoveFrameTrigger removes a single FrameTrigger implementation from the list of triggers. Order is not maintained.

func (*Television) RemovePixelRenderer added in v0.16.0 

func (tv *Television) RemovePixelRenderer(r PixelRenderer)

RemovePixelRenderer removes a single PixelRenderer implementation from the list of renderers. Order is not maintained.

func (*Television) RemoveRealtimeAudioMixer added in v0.16.0 

func (tv *Television) RemoveRealtimeAudioMixer(m RealtimeAudioMixer)

RemoveRealtimeAudioMixer removes a RealtimeAudioMixer implementation from the Television.

func (*Television) Reset 

func (tv *Television) Reset(keepFrameNum bool) error

Reset the television to an initial state.

func (*Television) SetEmulationState added in v0.15.0 

func (tv *Television) SetEmulationState(state emulation.State)

SetEmulationState is called by emulation whenever state changes. How we handle incoming signals depends on the current state.

func (*Television) SetFPS 

func (tv *Television) SetFPS(fps float32)

SetFPS requests the number frames per second. This overrides the frame rate of the specification. A negative value restores frame rate to the ideal value (the frequency of the incoming signal).

func (*Television) SetFPSCap 

func (tv *Television) SetFPSCap(limit bool) bool

SetFPSCap whether the emulation should wait for FPS limiter. Returns the setting as it was previously.

func (*Television) SetSpec 

func (tv *Television) SetSpec(spec string) error

SetSpec sets the television's specification. Will return an error if specification is not recognised.

Currently supported NTSC, PAL, PAL60 and AUTO. The empty string behaves like "AUTO".

func (*Television) SetSpecConditional added in v0.12.1 

func (tv *Television) SetSpecConditional(spec string) error

SetSpecConditional sets the television's specification if the original specification (not the current spec, the original) is "AUTO".

This is used when attaching a cartridge to the VCS and also when processing setup entries (see setup package, particularly the TV type).

func (*Television) Signal 

func (tv *Television) Signal(sig signal.SignalAttributes) error

Signal updates the current state of the television.

func (*Television) Snapshot 

func (tv *Television) Snapshot() *State

Snapshot makes a copy of the television state.

func (*Television) String 

func (tv *Television) String() string

type VCSReturnChannel added in v0.8.0 

type VCSReturnChannel interface {
	SetClockSpeed(tvSpec string) error
}

VCSReturnChannel is used to send information from the TV back to the parent console. Named because I think of it as being similar to the Audio Return Channel (ARC) present in modern TVs.

Source Files

View all Source files

Directories

Path Synopsis
Package coords represents and can work with television coorindates Coordinates represent the state of the emulation from the point of the television.
 Package coords represents and can work with television coorindates Coordinates represent the state of the emulation from the point of the television.
Package signal exposes the interface between the VCS and the television implementation.
 Package signal exposes the interface between the VCS and the television implementation.
Package specification contains the definitions, including colour, of the PAL and NTSC television protocols supported by the emulation.
 Package specification contains the definitions, including colour, of the PAL and NTSC television protocols supported by the emulation.

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