Port "move pixelate filter to gd_filter.c" (sync with upstream) (GH-17361)

Cf. <libgd/libgd@0f0894a>.

Author: cmb69

ext/gd/config.m4

@@ -233,7 +233,6 @@ if test "$PHP_GD" != "no"; then
       libgd/gd_io.c
       libgd/gd_jpeg.c
       libgd/gd_matrix.c
-      libgd/gd_pixelate.c
       libgd/gd_png.c
       libgd/gd_rotate.c
       libgd/gd_security.c

ext/gd/config.w32

@@ -57,7 +57,7 @@ if (PHP_GD != "no") {
 			gdft.c gd_gd2.c gd_gd.c gd_gif_in.c gd_gif_out.c gdhelpers.c gd_io.c gd_io_dp.c \
 			gd_io_file.c gd_io_ss.c gd_jpeg.c gdkanji.c gd_png.c gd_ss.c \
 			gdtables.c gd_topal.c gd_wbmp.c gdxpm.c wbmp.c gd_xbm.c gd_security.c gd_transform.c \
-			gd_filter.c gd_pixelate.c gd_rotate.c gd_color_match.c gd_webp.c gd_avif.c \
+			gd_filter.c gd_rotate.c gd_color_match.c gd_webp.c gd_avif.c \
 			gd_crop.c gd_interpolation.c gd_matrix.c gd_bmp.c gd_tga.c", "gd");
 		AC_DEFINE('HAVE_GD_BUNDLED', 1, "Define to 1 if gd extension uses GD library bundled in PHP.");
 		AC_DEFINE('HAVE_GD_PNG', 1, "Define to 1 if gd extension has PNG support.");

ext/gd/libgd/gd_filter.c

@@ -110,6 +110,62 @@ int gdImageScatterEx(gdImagePtr im, gdScatterPtr scatter)
 	return 1;
 }
 
+int gdImagePixelate(gdImagePtr im, int block_size, const unsigned int mode)
+{
+	int x, y;
+
+	if (block_size <= 0) {
+		return 0;
+	} else if (block_size == 1) {
+		return 1;
+	}
+	switch (mode) {
+	case GD_PIXELATE_UPPERLEFT:
+		for (y = 0; y < im->sy; y += block_size) {
+			for (x = 0; x < im->sx; x += block_size) {
+				if (gdImageBoundsSafe(im, x, y)) {
+					int c = gdImageGetPixel(im, x, y);
+					gdImageFilledRectangle(im, x, y, x + block_size - 1, y + block_size - 1, c);
+				}
+			}
+		}
+		break;
+	case GD_PIXELATE_AVERAGE:
+		for (y = 0; y < im->sy; y += block_size) {
+			for (x = 0; x < im->sx; x += block_size) {
+				int a, r, g, b, c;
+				int total;
+				int cx, cy;
+
+				a = r = g = b = c = total = 0;
+				/* sampling */
+				for (cy = 0; cy < block_size; cy++) {
+					for (cx = 0; cx < block_size; cx++) {
+						if (!gdImageBoundsSafe(im, x + cx, y + cy)) {
+							continue;
+						}
+						c = gdImageGetPixel(im, x + cx, y + cy);
+						a += gdImageAlpha(im, c);
+						r += gdImageRed(im, c);
+						g += gdImageGreen(im, c);
+						b += gdImageBlue(im, c);
+						total++;
+					}
+				}
+				/* drawing */
+				if (total > 0) {
+					c = gdImageColorResolveAlpha(im, r / total, g / total, b / total, a / total);
+					gdImageFilledRectangle(im, x, y, x + block_size - 1, y + block_size - 1, c);
+				}
+			}
+		}
+		break;
+	default:
+		return 0;
+	}
+	return 1;
+}
+
 /* invert src image */
 int gdImageNegate(gdImagePtr src)
 {