Sort transparent colors from colors.txt to front of lookup table. Makes it easier

to determine if a color index corresponds to a transparent color.

common/colors.go

@@ -9,12 +9,33 @@ import (
 	"fmt"
 	"image/color"
 	"os"
+	"sort"
 	"strings"
 )
 
 type Colors struct {
 	Colors      []color.RGBA
 	NameIndex   map[string]int32
+	Transparent int
+}
+
+type namedColor struct {
+	name  string
+	color color.RGBA
+}
+
+type sortByAlpha []namedColor
+
+func (colors sortByAlpha) Less(i, j int) bool {
+	return colors[i].color.A < colors[j].color.A
+}
+
+func (colors sortByAlpha) Len() int {
+	return len(colors)
+}
+
+func (colors sortByAlpha) Swap(i, j int) {
+	colors[i], colors[j] = colors[j], colors[i]
 }
 
 func ParseColors(filename string) (colors *Colors, err error) {
@@ -25,8 +46,7 @@ func ParseColors(filename string) (colors *Colors, err error) {
 	}
 	defer file.Close()
 
-	nameIndex := make(map[string]int32)
-	cols := make([]color.RGBA, 0, 2200)
+	cols := make([]namedColor, 0, 2200)
 
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
@@ -38,12 +58,26 @@ func ParseColors(filename string) (colors *Colors, err error) {
 		var name string
 		if n, _ := fmt.Sscanf(
 			line, "%s %d %d %d %d", &name, &c.R, &c.G, &c.B, &c.A); n > 0 {
-			idx := int32(len(cols))
-			cols = append(cols, c)
-			nameIndex[name] = idx
+			cols = append(cols, namedColor{name: name, color: c})
 		}
 	}
 	err = scanner.Err()
-	colors = &Colors{Colors: cols, NameIndex: nameIndex}
+
+	// Sort transparent colors to front. Makes it easier to figure out
+	// if an index corresponds to a transparent color (i < Transparent).
+	sort.Sort(sortByAlpha(cols))
+
+	cs := make([]color.RGBA, len(cols))
+	nameIndex := make(map[string]int32, len(cols))
+
+	transparent := 0
+	for i, nc := range cols {
+		if nc.color.A < 0xff {
+			transparent++
+		}
+		cs[i] = nc.color
+		nameIndex[nc.name] = int32(i)
+	}
+	colors = &Colors{Colors: cs, NameIndex: nameIndex, Transparent: transparent}
 	return
 }