internal/f32color: optimize LinearFromSRGB

Previously each call was ~100ns, the new implementation is ~1ns. Signed-off-by: Egon Elbre <egonelbre@gmail.com>
2022-07-01 22:09:16 +03:00
parent 2adf4efcbd
commit 3670f70c01
4 changed files with 109 additions and 3 deletions
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"math"
+	"os"
+)
+
+func main() {
+	out := flag.String("out", "", "output file")
+	flag.Parse()
+
+	var b bytes.Buffer
+	printf := func(content string, args ...interface{}) {
+		fmt.Fprintf(&b, content, args...)
+	}
+
+	printf("// SPDX-License-Identifier: Unlicense OR MIT\n\n")
+	printf("// Code generated by f32colorgen. DO NOT EDIT.\n")
+	printf("\n")
+	printf("package f32color\n\n")
+
+	printf("// table corresponds to sRGBToLinear(float32(index)/0xff)\n")
+	printf("var srgb8ToLinear = [...]float32{")
+	for b := 0; b <= 0xFF; b++ {
+		if b%0x10 == 0 {
+			printf("\n\t")
+		}
+		v := sRGBToLinear(float32(b) / 0xff)
+		printf("%#v,", v)
+	}
+	printf("\n}\n")
+
+	data, err := format.Source(b.Bytes())
+	if err != nil {
+		fmt.Fprint(os.Stderr, b.String())
+		panic(err)
+	}
+
+	err = os.WriteFile(*out, data, 0755)
+	if err != nil {
+		panic(err)
+	}
+}
+
+// sRGBToLinear transforms color value from sRGB to linear.
+func sRGBToLinear(c float32) float32 {
+	// Formula from EXT_sRGB.
+	if c <= 0.04045 {
+		return c / 12.92
+	} else {
+		return float32(math.Pow(float64((c+0.055)/1.055), 2.4))
+	}
+}