Port fix for libgd bug 276

The issue that BMP RLE occasionally swallowed some pixels[1] had been
fixed long ago in libgd, but apparently it has been overlooked to port
it to our bundled libgd.

We also introduce the test helper `test_image_equals_image()` which
compares in-memory images for equality.

[1] <https://github.com/libgd/libgd/issues/276>

Closes GH-17250.

NEWS

@@ -41,6 +41,8 @@ PHP                                                                        NEWS
 - GD:
   . Fixed bug GH-16255 (Unexpected nan value in ext/gd/libgd/gd_filter.c).
     (nielsdos, cmb)
+  . Ported fix for libgd bug 276 (Sometimes pixels are missing when storing
+    images as BMPs). (cmb)
 
 - Gettext:
   . Fixed bug GH-17202 (Segmentation fault ext/gettext/gettext.c

ext/gd/libgd/gd_bmp.c

@@ -350,9 +350,7 @@ static int compress_row(unsigned char *row, int length)
 	}
 
 	if (compressed_run) {
-		if (rle_type == BMP_RLE_TYPE_RLE) {
-			compressed_length += build_rle_packet(row, rle_type, compressed_run, uncompressed_row);
-		}
+		compressed_length += build_rle_packet(row, rle_type, compressed_run, uncompressed_row);
 	}
 
 	gdFree(uncompressed_start);

ext/gd/tests/func.inc

@@ -70,12 +70,8 @@ function get_libxpm_version()
  * message is printed, and the actual file is stored right beside the temporary
  * .php test file with the extension .out.png, to be able to manually inspect
  * the result.
- *
- * @param string $filename
- * @param resource $actual
- * @return void
  */
-function test_image_equals_file($filename, $actual)
+function test_image_equals_file(string $filename, GdImage $actual): void
 {
     if (!file_exists($filename)) {
         echo "The expected image does not exist.\n";
@@ -85,13 +81,29 @@ function test_image_equals_file($filename, $actual)
     $actual = test_to_truecolor($actual);
     $expected = imagecreatefrompng($filename);
     $expected = test_to_truecolor($expected);
+    test_image_equals_image($expected, $actual, true);
+}
+
+/**
+ * Tests that an in-memory image equals another in-memory image.
+ *
+ * It checks for equal image sizes, and whether any pixels are different.
+ * The textual result is printed, so the EXPECT section should contain the line
+ * "The images are equal."
+ *
+ * If the images are not equal, a diagnostic message is printed.
+ */
+function test_image_equals_image(GdImage $expected, GdImage $actual, bool $save_actual = false): void
+{
     $exp_x = imagesx($expected);
     $exp_y = imagesy($expected);
     $act_x = imagesx($actual);
     $act_y = imagesy($actual);
     if ($exp_x != $act_x || $exp_y != $act_y) {
         echo "The image size differs: expected {$exp_x}x{$exp_y}, got {$act_x}x{$act_y}.\n";
-        save_actual_image($actual);
+        if ($save_actual) {
+            save_actual_image($actual);
+        }
         return;
     }
     $pixels_changed = 0;
@@ -108,7 +120,9 @@ function test_image_equals_file($filename, $actual)
         echo "The images are equal.\n";
     } else {
         echo "The images differ in {$pixels_changed} pixels.\n";
-        save_actual_image($actual);
+        if ($save_actual) {
+            save_actual_image($actual);
+        }
     }
 }
 

ext/gd/tests/gd276.phpt

@@ -0,0 +1,26 @@
+--TEST--
+libgd bug 276 (Sometimes pixels are missing when storing images as BMPs)
+--EXTENSIONS--
+gd
+--FILE--
+<?php
+require __DIR__ . "/func.inc";
+
+$orig = imagecreate(10, 10);
+imagecolorallocate($orig, 0, 0, 0);
+$white = imagecolorallocate($orig, 255, 255, 255);
+imageline($orig, 0, 0, 99, 99, $white);
+
+$filename = __DIR__ . "/gd276.bmp";
+imagebmp($orig, $filename, true);
+$saved = imagecreatefrombmp($filename);
+var_dump($saved !== false);
+test_image_equals_image($orig, $saved);
+?>
+--EXPECT--
+bool(true)
+The images are equal.
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/gd276.bmp");
+?>