themes and styles

client/world/style_override_fingerprint.go

@@ -0,0 +1,96 @@
+package world
+
+import (
+	"hash"
+	"hash/fnv"
+	"image/color"
+	"math"
+)
+
+// hashU64 writes v to the hash in little-endian form.
+// We keep it manual to avoid extra allocations and dependencies.
+func hashU64(h hash.Hash64, v uint64) {
+	var b [8]byte
+	b[0] = byte(v)
+	b[1] = byte(v >> 8)
+	b[2] = byte(v >> 16)
+	b[3] = byte(v >> 24)
+	b[4] = byte(v >> 32)
+	b[5] = byte(v >> 40)
+	b[6] = byte(v >> 48)
+	b[7] = byte(v >> 56)
+	_, _ = h.Write(b[:])
+}
+
+func hashBool(h hash.Hash64, v bool) {
+	if v {
+		hashU64(h, 1)
+	} else {
+		hashU64(h, 0)
+	}
+}
+
+func hashColor(h hash.Hash64, c color.Color) {
+	if c == nil {
+		hashU64(h, 0)
+		return
+	}
+	r, g, b, a := c.RGBA()
+	hashU64(h, uint64(r))
+	hashU64(h, uint64(g))
+	hashU64(h, uint64(b))
+	hashU64(h, uint64(a))
+}
+
+// fingerprint returns a stable hash of the override content.
+//
+// Notes on semantics:
+//   - FillColor / StrokeColor: nil means "unset" (do not override). Transparent override is represented
+//     by a non-nil color with alpha=0.
+//   - Pointer fields (*float64, *[]float64) encode presence via nil/non-nil.
+//   - StrokeDashes: nil pointer means "unset"; non-nil pointer to nil slice means "set to nil".
+func (o StyleOverride) fingerprint() uint64 {
+	h := fnv.New64a() // returns hash.Hash64
+
+	// FillColor / StrokeColor
+	hashBool(h, o.FillColor != nil)
+	hashColor(h, o.FillColor)
+
+	hashBool(h, o.StrokeColor != nil)
+	hashColor(h, o.StrokeColor)
+
+	// StrokeWidthPx
+	hashBool(h, o.StrokeWidthPx != nil)
+	if o.StrokeWidthPx != nil {
+		hashU64(h, math.Float64bits(*o.StrokeWidthPx))
+	}
+
+	// StrokeDashes
+	hashBool(h, o.StrokeDashes != nil)
+	if o.StrokeDashes != nil {
+		ds := *o.StrokeDashes
+		if ds == nil {
+			// Explicitly set to nil slice
+			hashU64(h, 0xffffffffffffffff)
+		} else {
+			hashU64(h, uint64(len(ds)))
+			for _, v := range ds {
+				hashU64(h, math.Float64bits(v))
+			}
+		}
+	}
+
+	// StrokeDashOffset
+	hashBool(h, o.StrokeDashOffset != nil)
+	if o.StrokeDashOffset != nil {
+		hashU64(h, math.Float64bits(*o.StrokeDashOffset))
+	}
+
+	// PointRadiusPx
+	hashBool(h, o.PointRadiusPx != nil)
+	if o.PointRadiusPx != nil {
+		hashU64(h, math.Float64bits(*o.PointRadiusPx))
+	}
+
+	return h.Sum64()
+}