Impl EncodeGray.

webp/encode.go

@@ -2,6 +2,7 @@ package webp
 
 /*
 #include <stdlib.h>
+#include <string.h>
 #include <webp/encode.h>
 
 int writeWebP(uint8_t*, size_t, struct WebPPicture*);
@@ -14,6 +15,32 @@ static void free_WebPPicture(WebPPicture* webpPicture) {
 	free(webpPicture);
 }
 
+static int webpEncodeGray(WebPConfig *config, WebPPicture *picture) {
+	int ok = 0;
+	const int c_width = (picture->width + 1) >> 1;
+	const int c_height = (picture->height + 1) >> 1;
+	const int c_stride = c_width;
+	const int c_size = c_stride * c_height;
+	const int gray = 128;
+	uint8_t* chroma;
+
+	chroma = malloc(c_size);
+	if (!chroma) {
+		return 0;
+	}
+	memset(chroma, gray, c_size);
+
+	picture->u = chroma;
+	picture->v = chroma;
+	picture->uv_stride = c_stride;
+
+	ok = WebPEncode(config, picture);
+
+	free(chroma);
+
+	return ok;
+}
+
 static int webPConfigLosslessPreset(WebPConfig* webpConfig, int level) {
 #if WEBP_ENCODER_ABI_VERSION < 0x203
 	return 0;
@@ -447,6 +474,40 @@ func EncodeRGBA(w io.Writer, img image.Image, c *Config) (err error) {
 	return
 }
 
+func EncodeGray(w io.Writer, p *image.Gray, c *Config) (err error) {
+	if err = validateConfig(c); err != nil {
+		return
+	}
+
+	pic := C.malloc_WebPPicture()
+	if pic == nil {
+		return errors.New("Could not allocate webp picture")
+	}
+	defer C.free_WebPPicture(pic)
+
+	makeDestinationManager(w, pic)
+	defer releaseDestinationManager(pic)
+
+	if C.WebPPictureInit(pic) == 0 {
+		return errors.New("Could not initialize webp picture")
+	}
+	defer C.WebPPictureFree(pic)
+
+	pic.use_argb = 0
+	pic.width = C.int(p.Rect.Dx())
+	pic.height = C.int(p.Rect.Dy())
+	pic.y = (*C.uint8_t)(&p.Pix[0])
+	pic.y_stride = C.int(p.Stride)
+
+	pic.writer = C.WebPWriterFunction(C.writeWebP)
+
+	if C.webpEncodeGray(&c.c, pic) == 0 {
+		return fmt.Errorf("Encoding error: %d", pic.error_code)
+	}
+
+	return
+}
+
 // EncodeYUVA encodes and writes YUVA Image data into the writer as WebP.
 func EncodeYUVA(w io.Writer, img *YUVAImage, c *Config) (err error) {
 	if err = validateConfig(c); err != nil {

webp/webp_test.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"fmt"
 	"image"
+	"image/color"
 	"os"
 	"testing"
 
@@ -217,3 +218,27 @@ func TestEncodeYUVA(t *testing.T) {
 		return
 	}
 }
+
+func TestEncodeGray(t *testing.T) {
+	p := image.NewGray(image.Rect(0, 0, 1, 10))
+	for i := 0; i < 10; i++ {
+		p.SetGray(0, i, color.Gray{uint8(float32(i) / 10 * 255)})
+	}
+
+	f := util.CreateFile("TestEncodeGray.webp")
+	w := bufio.NewWriter(f)
+	defer func() {
+		w.Flush()
+		f.Close()
+	}()
+
+	config, err := webp.ConfigPreset(webp.PresetDefault, 100)
+	if err != nil {
+		t.Fatalf("got error: %v", err)
+	}
+
+	if err := webp.EncodeGray(w, p, config); err != nil {
+		t.Errorf("Got Error: %v", err)
+		return
+	}
+}