hints kitten: Workaround for some broken light color themes that make the hints text color too low contrast to read

Fixes #7330

docs/changelog.rst

@@ -89,6 +89,8 @@ Detailed list of changes
 
 - Splits layout: Allow setting the bias of the current split using ``layout_action bias`` (:iss:`8222`)
 
+- hints kitten: Workaround for some broken light color themes that make the hints text color too low contrast to read (:iss:`7330`)
+
 
 0.39.0 [2025-01-16]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

kittens/hints/main.go

@@ -111,7 +111,28 @@ func decode_hint(x string, alphabet string) (ans int) {
 	return
 }
 
+func as_rgb(c uint32) [3]float32 {
+	return [3]float32{float32((c>>16)&255) / 255.0, float32((c>>8)&255) / 255.0, float32(c&255) / 255.0}
+}
+
+func hints_text_color(confval string) (ans string) {
+	ans = confval
+	if ans == "auto" {
+		ans = "bright-gray"
+		if bc, err := tui.ReadBasicColors(); err == nil {
+			bg := as_rgb(bc.Background)
+			c15 := as_rgb(bc.Color15)
+			c8 := as_rgb(bc.Color8)
+			if utils.RGBContrast(bg[0], bg[1], bg[2], c8[0], c8[1], c8[2]) > utils.RGBContrast(bg[0], bg[1], bg[2], c15[0], c15[1], c15[2]) {
+				ans = "bright-black"
+			}
+		}
+	}
+	return
+}
+
 func main(_ *cli.Command, o *Options, args []string) (rc int, err error) {
+	o.HintsTextColor = hints_text_color(o.HintsTextColor)
 	output := tui.KittenOutputSerializer()
 	if tty.IsTerminal(os.Stdin.Fd()) {
 		return 1, fmt.Errorf("You must pass the text to be hinted on STDIN")

kittens/hints/main.py

@@ -229,11 +229,11 @@ color.
 
 
 --hints-text-color
-default=bright-gray
+default=auto
 type=str
 The foreground color for text pointed to by the hints. You can use color names or hex values. For the eight basic
 named terminal colors you can also use the :code:`bright-` prefix to get the bright variant of the
-color.
+color. The default is to pick a suitable color automatically.
 
 
 --customize-processing

tools/tui/ui_kitten.go

@@ -20,6 +20,37 @@ var RunningAsUI = sync.OnceValue(func() bool {
 	return os.Getenv("KITTEN_RUNNING_AS_UI") != ""
 })
 
+type BasicColors struct {
+	Foreground uint32 `json:"foreground"`
+	Background uint32 `json:"background"`
+	Color0     uint32 `json:"color0"`
+	Color1     uint32 `json:"color1"`
+	Color2     uint32 `json:"color2"`
+	Color3     uint32 `json:"color3"`
+	Color4     uint32 `json:"color4"`
+	Color5     uint32 `json:"color5"`
+	Color6     uint32 `json:"color6"`
+	Color7     uint32 `json:"color7"`
+	Color8     uint32 `json:"color8"`
+	Color9     uint32 `json:"color9"`
+	Color10    uint32 `json:"color10"`
+	Color11    uint32 `json:"color11"`
+	Color12    uint32 `json:"color12"`
+	Color13    uint32 `json:"color13"`
+	Color14    uint32 `json:"color14"`
+	Color15    uint32 `json:"color15"`
+}
+
+func ReadBasicColors() (ans BasicColors, err error) {
+	q := os.Getenv("KITTY_BASIC_COLORS")
+	if q == "" {
+		err = fmt.Errorf("No KITTY_BASIC_COLORS env var")
+	} else {
+		err = json.Unmarshal(utils.UnsafeStringToBytes(q), &ans)
+	}
+	return
+}
+
 func PrepareRootCmd(root *cli.Command) {
 	if RunningAsUI() {
 		root.CallbackOnError = func(cmd *cli.Command, err error, during_parsing bool, exit_code int) int {

tools/utils/colors.go

@@ -0,0 +1,21 @@
+package utils
+
+import (
+	"fmt"
+)
+
+var _ = fmt.Print
+
+func RGBLuminance(r, g, b float32) float32 {
+	// From ITU BT 601 https://www.itu.int/rec/R-REC-BT.601
+	return 0.299*r + 0.587*g + 0.114*b
+}
+
+func RGBContrast(r1, g1, b1, r2, g2, b2 float32) float32 {
+	al := RGBLuminance(r1, g1, b1)
+	bl := RGBLuminance(r2, g2, b2)
+	if al < bl {
+		al, bl = bl, al
+	}
+	return (al + 0.05) / (bl + 0.05)
+}