Color-related APIs design

[nighca]

Existed APIs

Type Color (spx v1)

alias for image/color.RGBA

type RGBA struct {
  R, G, B, A uint8
}

func (c RGBA) RGBA() (r, g, b, a uint32)

Utils (spx v1)

• RGB(r, g, b uint8) Color
• RGBA(r, g, b, a uint8) Color

Touching (spx v1)

• TouchingColor(color Color) bool

Pen (Scratch < v3)

• Set Pen Color to (value): value in range [0, 200]
• Change Pen Color by (delta)
• Set Pen Shade to (value): value in range [0, 200]
• Change Pen Shade by (delta)

Pen (spx v1)

• SetPenColor(color Color)
• ChangePenColor(delta float64) (not implemented)
• SetPenShade(shade float64)
• ChangePenShade(delta float64)
• SetPenHue(hue float64)
• ChangePenHue(delta float64)

Pen (Scratch v3)

• Set Pen Color to ()
• Set Pen (color|saturation|brightness|ghost) to (): value in range [0, 100]
• Change Pen (color|saturation|brightness|ghost) by ()

Effects (Scratch v3)

• Set (color|brightness|ghost) effect to ()
• Change (color|brightness|ghost) effect by ()
  • for color(hue), range [0, 200] is used
  • for brightness, range [-100, 100] is used
  • for ghost(transparency), range [0, 100] is used

Proposal for spx v2

Use HSB instead of RGB as the main color model:

• When providing color picker in UI, use HSB
• When providing detailed-color-manipulation APIs, use HSB
• Provide utility functions to generate color value based on HSB value

Provide APIs as below:

Type Color

type Color struct {
  // no exported fields or methods
}

Utils

func RGB(r, g, b uint8) Color
func RGBA(r, g, b, a uint8) Color

// h, s, b, a in range [0, 100], just like Scratch
func HSB(h, s, b float64) Color
func HSBA(h, s, b, a float64) Color

Touching

func TouchingColor(color Color) bool

Pen

type PenColorParam int

const (
	PenHue PenColorParam = iota
	PenSaturation
	PenBrightness
)

func SetPenColor(color Color)
func SetPenColor(param PenColorParam, value float64)
func ChangePenColor(param PenColorParam, delta float64)

range [0, 100] is used for hue, saturation, and brightness

Effects

type EffectKind int

const (
  ColorEffect EffectKind = iota
  BrightnessEffect
  GhostEffect
  // ...
)

func SetEffect(kind EffectKind, value float64)
func ChangeEffect(kind EffectKind, delta float64)

• for color(hue), range [0, 200] is used
• for brightness, range [-100, 100] is used
• for ghost(transparency), range [0, 100] is used