Remove basically effectless gdImageAABlend()

This had already be done for GD 2.0.26 as part of the improved antialiasing
support (<https://boutell.com/gd/manual2.0.26.html#whatsnew2.0.26>).

ext/gd/libgd/gd.c

@@ -1018,46 +1018,7 @@ int gdImageGetPixel (gdImagePtr im, int x, int y)
 
 void gdImageAABlend (gdImagePtr im)
 {
-	float p_alpha, old_alpha;
-	int color = im->AA_color, color_red, color_green, color_blue;
-	int old_color, old_red, old_green, old_blue;
-	int p_color, p_red, p_green, p_blue;
-	int px, py;
-
-	color_red = gdImageRed(im, color);
-	color_green = gdImageGreen(im, color);
-	color_blue = gdImageBlue(im, color);
-
-	/* Impose the anti-aliased drawing on the image. */
-	for (py = 0; py < im->sy; py++) {
-		for (px = 0; px < im->sx; px++) {
-			if (im->AA_opacity[py][px] != 0) {
-				old_color = gdImageGetPixel(im, px, py);
-
-				if ((old_color != color) && ((old_color != im->AA_dont_blend) || (im->AA_opacity[py][px] == 255))) {
-					/* Only blend with different colors that aren't the dont_blend color. */
-					p_alpha = (float) (im->AA_opacity[py][px]) / 255.0;
-					old_alpha = 1.0 - p_alpha;
-
-					if (p_alpha >= 1.0) {
-						p_color = color;
-					} else {
-						old_red = gdImageRed(im, old_color);
-						old_green = gdImageGreen(im, old_color);
-						old_blue = gdImageBlue(im, old_color);
-
-						p_red = (int) (((float) color_red * p_alpha) + ((float) old_red * old_alpha));
-						p_green = (int) (((float) color_green * p_alpha) + ((float) old_green * old_alpha));
-						p_blue = (int) (((float) color_blue * p_alpha) + ((float) old_blue * old_alpha));
-						p_color = gdImageColorResolve(im, p_red, p_green, p_blue);
-					}
-					gdImageSetPixel(im, px, py, p_color);
-				}
-			}
-		}
-		/* Clear the AA_opacity array behind us. */
-		memset(im->AA_opacity[py], 0, im->sx);
-	}
+	(void)im;
 }
 
 static void _gdImageFilledHRectangle (gdImagePtr im, int x1, int y1, int x2, int y2, int color);
@@ -2743,7 +2704,6 @@ void gdImagePolygon (gdImagePtr im, gdPointPtr p, int n, int c)
 
 	if (c == gdAntiAliased) {
 		im->AA_polygon = 0;
-		gdImageAABlend(im);
 	}
 }
 

ext/gd/tests/imagepolygon_aa.phpt

@@ -0,0 +1,24 @@
+--TEST--
+antialiased imagepolygon()
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+require_once __DIR__ . DIRECTORY_SEPARATOR . 'func.inc';
+
+$im = imagecreatetruecolor(100, 100);
+$white = imagecolorallocate($im, 255, 255, 255);
+$black = imagecolorallocate($im, 0, 0, 0);
+imagefilledrectangle($im, 0,0, 99,99, $white);
+imageantialias($im, true);
+
+imagepolygon($im, [10,10, 49,89, 89,49], 3, $black);
+
+test_image_equals_file(__DIR__ . DIRECTORY_SEPARATOR . 'imagepolygon_aa.png', $im);
+?>
+===DONE===
+--EXPECT--
+The images are equal.
+===DONE===