diff options
Diffstat (limited to 'src/pkg/image/color.go')
| -rw-r--r-- | src/pkg/image/color.go | 69 |
1 files changed, 21 insertions, 48 deletions
diff --git a/src/pkg/image/color.go b/src/pkg/image/color.go index 31ba59280..c17ffc389 100644 --- a/src/pkg/image/color.go +++ b/src/pkg/image/color.go @@ -4,14 +4,15 @@ package image -// TODO(nigeltao): Think about how floating-point color models work. - -// All Colors can convert themselves, with a possible loss of precision, to 128-bit alpha-premultiplied RGBA. +// All Colors can convert themselves, with a possible loss of precision, +// to 64-bit alpha-premultiplied RGBA. Each channel value ranges within +// [0, 0xFFFF]. type Color interface { RGBA() (r, g, b, a uint32) } -// An RGBAColor represents a traditional 32-bit alpha-premultiplied color, having 8 bits for each of red, green, blue and alpha. +// An RGBAColor represents a traditional 32-bit alpha-premultiplied color, +// having 8 bits for each of red, green, blue and alpha. type RGBAColor struct { R, G, B, A uint8 } @@ -19,34 +20,23 @@ type RGBAColor struct { func (c RGBAColor) RGBA() (r, g, b, a uint32) { r = uint32(c.R) r |= r << 8 - r |= r << 16 g = uint32(c.G) g |= g << 8 - g |= g << 16 b = uint32(c.B) b |= b << 8 - b |= b << 16 a = uint32(c.A) a |= a << 8 - a |= a << 16 return } -// An RGBA64Color represents a 64-bit alpha-premultiplied color, having 16 bits for each of red, green, blue and alpha. +// An RGBA64Color represents a 64-bit alpha-premultiplied color, +// having 16 bits for each of red, green, blue and alpha. type RGBA64Color struct { R, G, B, A uint16 } func (c RGBA64Color) RGBA() (r, g, b, a uint32) { - r = uint32(c.R) - r |= r << 16 - g = uint32(c.G) - g |= g << 16 - b = uint32(c.B) - b |= b << 16 - a = uint32(c.A) - a |= a << 16 - return + return uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A) } // An NRGBAColor represents a non-alpha-premultiplied 32-bit color. @@ -59,24 +49,21 @@ func (c NRGBAColor) RGBA() (r, g, b, a uint32) { r |= r << 8 r *= uint32(c.A) r /= 0xff - r |= r << 16 g = uint32(c.G) g |= g << 8 g *= uint32(c.A) g /= 0xff - g |= g << 16 b = uint32(c.B) b |= b << 8 b *= uint32(c.A) b /= 0xff - b |= b << 16 a = uint32(c.A) a |= a << 8 - a |= a << 16 return } -// An NRGBA64Color represents a non-alpha-premultiplied 64-bit color, having 16 bits for each of red, green, blue and alpha. +// An NRGBA64Color represents a non-alpha-premultiplied 64-bit color, +// having 16 bits for each of red, green, blue and alpha. type NRGBA64Color struct { R, G, B, A uint16 } @@ -85,18 +72,13 @@ func (c NRGBA64Color) RGBA() (r, g, b, a uint32) { r = uint32(c.R) r *= uint32(c.A) r /= 0xffff - r |= r << 16 g = uint32(c.G) g *= uint32(c.A) g /= 0xffff - g |= g << 16 b = uint32(c.B) b *= uint32(c.A) b /= 0xffff - b |= b << 16 a = uint32(c.A) - a |= a << 8 - a |= a << 16 return } @@ -108,12 +90,11 @@ type AlphaColor struct { func (c AlphaColor) RGBA() (r, g, b, a uint32) { a = uint32(c.A) a |= a << 8 - a |= a << 16 return a, a, a, a } -// A ColorModel can convert foreign Colors, with a possible loss of precision, to a Color -// from its own color model. +// A ColorModel can convert foreign Colors, with a possible loss of precision, +// to a Color from its own color model. type ColorModel interface { Convert(c Color) Color } @@ -129,36 +110,32 @@ func (f ColorModelFunc) Convert(c Color) Color { } func toRGBAColor(c Color) Color { - if _, ok := c.(RGBAColor); ok { // no-op conversion + if _, ok := c.(RGBAColor); ok { return c } r, g, b, a := c.RGBA() - return RGBAColor{uint8(r >> 24), uint8(g >> 24), uint8(b >> 24), uint8(a >> 24)} + return RGBAColor{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), uint8(a >> 8)} } func toRGBA64Color(c Color) Color { - if _, ok := c.(RGBA64Color); ok { // no-op conversion + if _, ok := c.(RGBA64Color); ok { return c } r, g, b, a := c.RGBA() - return RGBA64Color{uint16(r >> 16), uint16(g >> 16), uint16(b >> 16), uint16(a >> 16)} + return RGBA64Color{uint16(r), uint16(g), uint16(b), uint16(a)} } func toNRGBAColor(c Color) Color { - if _, ok := c.(NRGBAColor); ok { // no-op conversion + if _, ok := c.(NRGBAColor); ok { return c } r, g, b, a := c.RGBA() - a >>= 16 if a == 0xffff { - return NRGBAColor{uint8(r >> 24), uint8(g >> 24), uint8(b >> 24), 0xff} + return NRGBAColor{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), 0xff} } if a == 0 { return NRGBAColor{0, 0, 0, 0} } - r >>= 16 - g >>= 16 - b >>= 16 // Since Color.RGBA returns a alpha-premultiplied color, we should have r <= a && g <= a && b <= a. r = (r * 0xffff) / a g = (g * 0xffff) / a @@ -167,14 +144,10 @@ func toNRGBAColor(c Color) Color { } func toNRGBA64Color(c Color) Color { - if _, ok := c.(NRGBA64Color); ok { // no-op conversion + if _, ok := c.(NRGBA64Color); ok { return c } r, g, b, a := c.RGBA() - a >>= 16 - r >>= 16 - g >>= 16 - b >>= 16 if a == 0xffff { return NRGBA64Color{uint16(r), uint16(g), uint16(b), 0xffff} } @@ -189,11 +162,11 @@ func toNRGBA64Color(c Color) Color { } func toAlphaColor(c Color) Color { - if _, ok := c.(AlphaColor); ok { // no-op conversion + if _, ok := c.(AlphaColor); ok { return c } _, _, _, a := c.RGBA() - return AlphaColor{uint8(a >> 24)} + return AlphaColor{uint8(a >> 8)} } // The ColorModel associated with RGBAColor. |