Lossless conversion for webp

Propagating lossless conversion from libgd to our bundled gd.
Changing "quantization" to "quality" as in libgd.
Adding test.

IMG_WEBP_LOSSLESS is only defined, if lossless WebP encoding is
supported by the libgd used.

Closes GH-7348.

Author: morsssss

UPGRADING

@@ -562,6 +562,11 @@ PHP 8.1 UPGRADE NOTES
 9. Other Changes to Extensions
 ========================================
 
+- GD:
+  imagewebp() can do lossless WebP encoding by passing IMG_WEBP_LOSSLESS as
+  quality. This constant is only defined, if a libgd is used which supports
+  lossless WebP encoding.
+
 - MySQLi:
   . The mysqli_stmt::next_result() and mysqli::fetch_all() methods are now
     available when linking against libmysqlclient.

ext/gd/config.m4

@@ -92,7 +92,7 @@ AC_DEFUN([PHP_GD_AVIF],[
 
 AC_DEFUN([PHP_GD_WEBP],[
   if test "$PHP_WEBP" != "no"; then
-    PKG_CHECK_MODULES([WEBP], [libwebp])
+    PKG_CHECK_MODULES([WEBP], [libwebp >= 0.2.0])
     PHP_EVAL_LIBLINE($WEBP_LIBS, GD_SHARED_LIBADD)
     PHP_EVAL_INCLINE($WEBP_CFLAGS)
     AC_DEFINE(HAVE_LIBWEBP, 1, [ ])

ext/gd/gd.c

@@ -378,6 +378,11 @@ PHP_MINIT_FUNCTION(gd)
 	REGISTER_LONG_CONSTANT("IMG_BMP", PHP_IMG_BMP, CONST_CS | CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("IMG_TGA", PHP_IMG_TGA, CONST_CS | CONST_PERSISTENT);
 
+#ifdef gdWebpLossless
+	/* constant for webp encoding */
+	REGISTER_LONG_CONSTANT("IMG_WEBP_LOSSLESS", gdWebpLossless, CONST_CS | CONST_PERSISTENT);
+#endif
+
 	/* special colours for gd */
 	REGISTER_LONG_CONSTANT("IMG_COLOR_TILED", gdTiled, CONST_CS | CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("IMG_COLOR_STYLED", gdStyled, CONST_CS | CONST_PERSISTENT);

ext/gd/libgd/gd.h

@@ -619,7 +619,20 @@ void *gdImageWBMPPtr(gdImagePtr im, int *size, int fg);
 void gdImageJpeg(gdImagePtr im, FILE *out, int quality);
 void gdImageJpegCtx(gdImagePtr im, gdIOCtx *out, int quality);
 
-void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quantization);
+/**
+ * Group: WebP
+ *
+ * Constant: gdWebpLossless
+ *
+ * Lossless quality threshold. When image quality is greater than or equal to
+ * <gdWebpLossless>, the image will be written in the lossless WebP format.
+ *
+ * See also:
+ *   - <gdImageWebpCtx>
+ */
+#define gdWebpLossless 101
+
+void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quality);
 
 /* Best to free this memory with gdFree(), not free() */
 void *gdImageJpegPtr(gdImagePtr im, int *size, int quality);

ext/gd/libgd/gd_webp.c

@@ -100,7 +100,7 @@ gdImagePtr gdImageCreateFromWebpCtx (gdIOCtx * infile)
 	return im;
 }
 
-void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quantization)
+void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quality)
 {
 	uint8_t *argb;
 	int x, y;
@@ -117,8 +117,8 @@ void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quantization)
 		return;
 	}
 
-	if (quantization == -1) {
-		quantization = 80;
+	if (quality == -1) {
+		quality = 80;
 	}
 
 	if (overflow2(gdImageSX(im), 4)) {
@@ -151,7 +151,13 @@ void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quantization)
 			*(p++) = a;
 		}
 	}
-	out_size = WebPEncodeRGBA(argb, gdImageSX(im), gdImageSY(im), gdImageSX(im) * 4, quantization, &out);
+	
+	if (quality >= gdWebpLossless) {
+		out_size = WebPEncodeLosslessRGBA(argb, gdImageSX(im), gdImageSY(im), gdImageSX(im) * 4, &out);
+	} else {
+		out_size = WebPEncodeRGBA(argb, gdImageSX(im), gdImageSY(im), gdImageSX(im) * 4, quality, &out);
+	}
+
 	if (out_size == 0) {
 		zend_error(E_ERROR, "gd-webp encoding failed");
 		goto freeargb;
@@ -163,10 +169,10 @@ void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quantization)
 	gdFree(argb);
 }
 
-void gdImageWebpEx (gdImagePtr im, FILE * outFile, int quantization)
+void gdImageWebpEx (gdImagePtr im, FILE * outFile, int quality)
 {
 	gdIOCtx *out = gdNewFileCtx(outFile);
-	gdImageWebpCtx(im, out, quantization);
+	gdImageWebpCtx(im, out, quality);
 	out->gd_free(out);
 }
 
@@ -188,11 +194,11 @@ void * gdImageWebpPtr (gdImagePtr im, int *size)
 	return rv;
 }
 
-void * gdImageWebpPtrEx (gdImagePtr im, int *size, int quantization)
+void * gdImageWebpPtrEx (gdImagePtr im, int *size, int quality)
 {
 	void *rv;
 	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
-	gdImageWebpCtx(im, out, quantization);
+	gdImageWebpCtx(im, out, quality);
 	rv = gdDPExtractData(out, size);
 	out->gd_free(out);
 	return rv;

ext/gd/tests/webp_basic.phpt

@@ -29,11 +29,19 @@ imagewebp($im1, $filename);
 
 $im2 = imagecreatefromwebp($filename);
 imagewebp($im2, $filename);
+echo 'Is lossy conversion close enough? ';
 var_dump(calc_image_dissimilarity($im1, $im2) < 10e5);
+
+imagewebp($im1, $filename, IMG_WEBP_LOSSLESS);
+$im_lossless = imagecreatefromwebp($filename);
+echo 'Does lossless conversion work? ';
+var_dump(calc_image_dissimilarity($im1, $im_lossless) == 0);
+
 ?>
 --CLEAN--
 <?php
 @unlink(__DIR__ . '/webp_basic.webp');
 ?>
 --EXPECT--
-bool(true)
+Is lossy conversion close enough? bool(true)
+Does lossless conversion work? bool(true)