v0.1.0 initial commit

color.go

@@ -0,0 +1,115 @@
+package terminal
+
+// ColorMode indicates terminal color capability
+type ColorMode uint8
+
+const (
+	ColorMode256       ColorMode = iota // xterm-256 palette
+	ColorModeTrueColor                  // 24-bit RGB
+)
+
+// RGB represents a 24-bit color
+type RGB struct {
+	R uint8 `toml:"r"`
+	G uint8 `toml:"g"`
+	B uint8 `toml:"b"`
+}
+
+// Lerp linearly interpolates from c to other by t, clamped to [0,1]
+func (c RGB) Lerp(other RGB, t float64) RGB {
+	if t <= 0 {
+		return c
+	}
+	if t >= 1 {
+		return other
+	}
+	return RGB{
+		R: clampU8(float64(c.R) + (float64(other.R)-float64(c.R))*t),
+		G: clampU8(float64(c.G) + (float64(other.G)-float64(c.G))*t),
+		B: clampU8(float64(c.B) + (float64(other.B)-float64(c.B))*t),
+	}
+}
+
+// RGBBlack is the zero value black color
+var RGBBlack = RGB{0, 0, 0}
+
+// 6-bit quantized LUT for Redmean-based 256-color mapping
+// 64×64×64 = 262,144 bytes, fits in L2 cache
+var lut256 [64 * 64 * 64]uint8
+
+func init() {
+	// Pre-compute Redmean-based palette mapping for all 6-bit quantized RGB values
+	for r := 0; r < 64; r++ {
+		for g := 0; g < 64; g++ {
+			for b := 0; b < 64; b++ {
+				// Expand 6-bit to 8-bit (shift left 2, add 2 for midpoint)
+				r8 := (r << 2) | 2
+				g8 := (g << 2) | 2
+				b8 := (b << 2) | 2
+				lut256[r<<12|g<<6|b] = computeRedmean256(r8, g8, b8)
+			}
+		}
+	}
+}
+
+// computeRedmean256 finds the nearest 256-palette index using Redmean distance
+// Called only at init() to populate LUT
+func computeRedmean256(r, g, b int) uint8 {
+	// Grayscale fast path
+	if r == g && g == b {
+		if r < 8 {
+			return 16
+		}
+		if r > 238 {
+			return 231
+		}
+		return uint8(232 + (r-8)/10)
+	}
+
+	bestIdx := uint8(16)
+	minDist := 1 << 30
+
+	// Search 6×6×6 cube (indices 16-231)
+	for i := 0; i < 216; i++ {
+		cr := cubeValues[i/36]
+		cg := cubeValues[(i/6)%6]
+		cb := cubeValues[i%6]
+
+		d := redmeanDistance(r, g, b, cr, cg, cb)
+		if d < minDist {
+			minDist = d
+			bestIdx = uint8(16 + i)
+		}
+	}
+
+	// Search grayscale ramp (indices 232-255)
+	for i := 0; i < 24; i++ {
+		gray := 8 + i*10
+		d := redmeanDistance(r, g, b, gray, gray, gray)
+		if d < minDist {
+			minDist = d
+			bestIdx = uint8(232 + i)
+		}
+	}
+
+	return bestIdx
+}
+
+// redmeanDistance calculates perceptually-weighted color distance
+// Formula: https://en.wikipedia.org/wiki/Color_difference#sRGB
+func redmeanDistance(r1, g1, b1, r2, g2, b2 int) int {
+	rmean := (r1 + r2) / 2
+	dr := r1 - r2
+	dg := g1 - g2
+	db := b1 - b2
+	return (((512 + rmean) * dr * dr) >> 8) + 4*dg*dg + (((767 - rmean) * db * db) >> 8)
+}
+
+// Color cube values for 6×6×6 palette (indices 16-231)
+var cubeValues = [6]int{0, 95, 135, 175, 215, 255}
+
+// RGBTo256 converts RGB to nearest 256-color palette index
+// O(1) lookup via pre-computed Redmean LUT
+func RGBTo256(c RGB) uint8 {
+	return lut256[int(c.R>>2)<<12|int(c.G>>2)<<6|int(c.B>>2)]
+}