specification

Documentation

Overview

Package specification contains the definitions, including colour, of the PAL and NTSC television protocols supported by the emulation.

Index

• Constants
• Variables
• type Spec
  • func (spec *Spec) GetColor(col signal.ColorSignal) color.RGBA

Constants

const (
	ClksHBlank   = 68
	ClksVisible  = 160
	ClksScanline = 228
)

From the Stella Programmer's Guide:

"Each scan lines starts with 68 clock counts of horizontal blank (not seen on the TV screen) followed by 160 clock counts to fully scan one line of TV picture. When the electron beam reaches the end of a scan line, it returns to the left side of the screen, waits for the 68 horizontal blank clock counts, and proceeds to draw the next line below."

Clock counts are the same for both TV specifications. Vertical information should be accessed via SpecNTSC or SpecPAL.

const AbsoluteMaxScanlines = 312

the absolute number of scanlines allowed by the TV regardless of specification - value of 32 is the same as the total number of scanlines used by the PAL specification.

Variables

var PaletteNTSC = []color.RGBA{}

PaletteNTSC is the collection of NTSC colours.

var PalettePAL = []color.RGBA{}

PalettePAL is the collection of PAL colours.

var SpecList = []string{"NTSC", "PAL"}

SpecList is the list of specifications that the television may adopt.

Types

type Spec

type Spec struct {
	ID     string
	Colors []color.RGBA

	// the number of scanlines the 2600 Programmer's guide recommends for the
	// top/bottom parts of the screen:
	//
	// "A typical frame will consists of 3 vertical sync (VSYNC) lines*, 37 vertical
	// blank (VBLANK) lines, 192 TV picture lines, and 30 overscan lines. Atari’s
	// research has shown that this pattern will work on all types of TV sets."
	//
	// the above figures are in reference to the NTSC protocol
	ScanlinesVSync int

	ScanlinesVisible  int
	ScanlinesOverscan int

	// the total number of scanlines for the entire frame is the sum of the
	// four individual portions
	ScanlinesTotal int

	// the scanline at which the VBLANK should be turned off (Top) and
	// turned back on again (Bottom). the period between the top and bottom
	// scanline is the visible portion of the screen.
	//
	// in practice, the VCS can turn VBLANK on and off at any time; what the
	// two values below represent what "Atari's research" has shown to be safe.
	// by definition this means that:
	//
	//	Top = VSync + Vblank
	//
	//	Bottom = Top + Visible
	//
	// or
	//
	//	Bottom = Total - Overscan
	AtariSafeTop    int
	AtariSafeBottom int

	// resizing of the TV is problematic because we can't rely on the VBLANK to
	// tell us when the pixels are meant to be in view. The NewSafeTop
	// an NewSafeBottom are the min/max values that the resizer should
	// allow.
	NewSafeTop    int
	NewSafeBottom int

	// AaspectBias transforms the scaling factor for the X axis.
	// values taken from Stella emulator. useful for A/B testing
	AspectBias float32

	// the number of frames per second required by the specification
	FramesPerSecond float32
	// contains filtered or unexported fields
}

Spec is used to define the two television specifications.

var SpecNTSC Spec

SpecNTSC is the specification for NTSC television types.

var SpecPAL Spec

SpecPAL is the specification for PAL television types.

func (*Spec) GetColor

func (spec *Spec) GetColor(col signal.ColorSignal) color.RGBA

GetColor translates a signals to the color type.