feat: add color fade function and RBG (#34)

internal/map_range_to_range.go

@@ -0,0 +1,5 @@
+package internal
+
+func MapRangeToRange(fromMin, fromMax, toMin, toMax, current float32) int {
+	return int(toMin + ((toMax-toMin)/(fromMax-fromMin))*(current-fromMin))
+}

internal/map_range_to_range_test.go

@@ -0,0 +1,13 @@
+package internal
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestMapRangeToRange(t *testing.T) {
+	assert.Equal(t, 127, MapRangeToRange(0, 100, 0, 255, 50))
+	assert.Equal(t, 127, MapRangeToRange(0, 400, 0, 255, 200))
+	assert.Equal(t, 127, MapRangeToRange(-200, 200, 0, 255, 0))
+	assert.Equal(t, 127, MapRangeToRange(0, 200.123, 0, 254.3, 100))
+}

rgb.go

@@ -0,0 +1,26 @@
+package pterm
+
+import "github.com/pterm/pterm/internal"
+
+// RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors.
+// The name of the model comes from the initials of the three additive primary colors, red, green, and blue.
+// https://en.wikipedia.org/wiki/RGB_color_model
+type RGB struct {
+	R uint8
+	G uint8
+	B uint8
+}
+
+// NewRGB returns a new RGB.
+func NewRGB(r, g, b uint8) RGB {
+	return RGB{R: r, G: g, B: b}
+}
+
+// Fade fades one RGB value to another RGB value, by giving the function a minimum, maximum and current value.
+func (rgb RGB) Fade(min, max, current float32, end RGB) RGB {
+	return RGB{
+		R: uint8(internal.MapRangeToRange(min, max, float32(rgb.R), float32(end.R), current)),
+		G: uint8(internal.MapRangeToRange(min, max, float32(rgb.G), float32(end.G), current)),
+		B: uint8(internal.MapRangeToRange(min, max, float32(rgb.B), float32(end.B), current)),
+	}
+}