Add imagegetinterpolation()

While `imagesetinterpolation()` is available as of PHP 5.5.0,
there is no according getter function, so users would have to track the
current interpolation method manually.

To remedy this, we introduce `imagegetinterpolation()` as thin wrapper
for `gdImageGetInterpolationMethod()` (which has been introduced with
libgd 2.1.1), and use `im->interpolation_id` as fallback for older
libgd.  Since our bundled libgd does not yet have this function, we add
it.

We also simplify the recently introduced bug79068.phpt, where it is
sufficient to check that the interpolation method has not been changed.

NEWS

@@ -26,6 +26,7 @@ PHP                                                                        NEWS
   . Made the $num_points parameter of php_imagepolygon optional. (cmb)
   . Removed deprecated image2wbmp(). (cmb)
   . Removed deprecated png2wbmp() and jpeg2wbmp(). (cmb)
+  . Added imagegetinterpolation(). (cmb)
 
 - Intl:
   . Removed deprecated INTL_IDNA_VARIANT_2003. (cmb)

UPGRADING

@@ -394,6 +394,8 @@ PHP 8.0 UPGRADE NOTES
     imagefilledpolygon() is now optional, i.e. these functions may be called
     with either 3 or 4 arguments. If the arguments is omitted, it is calculated
     as count($points)/2.
+  . The function imagegetinterpolation() to get the current interpolation method
+    has been added.
 
 ========================================
 10. New Global Constants

ext/gd/config.m4

@@ -120,14 +120,15 @@ AC_DEFUN([PHP_GD_JISX0208],[
 ])
 
 AC_DEFUN([PHP_GD_CHECK_VERSION],[
-  PHP_CHECK_LIBRARY(gd, gdImageCreateFromPng,   [AC_DEFINE(HAVE_GD_PNG,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdImageCreateFromWebp,  [AC_DEFINE(HAVE_GD_WEBP,             1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdImageCreateFromJpeg,  [AC_DEFINE(HAVE_GD_JPG,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdImageCreateFromXpm,   [AC_DEFINE(HAVE_GD_XPM,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdImageCreateFromBmp,   [AC_DEFINE(HAVE_GD_BMP,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdImageCreateFromTga,   [AC_DEFINE(HAVE_GD_TGA,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdImageStringFT,        [AC_DEFINE(HAVE_GD_FREETYPE,         1, [ ])], [], [ $GD_SHARED_LIBADD ])
-  PHP_CHECK_LIBRARY(gd, gdVersionString,        [AC_DEFINE(HAVE_GD_LIBVERSION,       1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageCreateFromPng,          [AC_DEFINE(HAVE_GD_PNG,               1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageCreateFromWebp,         [AC_DEFINE(HAVE_GD_WEBP,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageCreateFromJpeg,         [AC_DEFINE(HAVE_GD_JPG,               1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageCreateFromXpm,          [AC_DEFINE(HAVE_GD_XPM,               1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageCreateFromBmp,          [AC_DEFINE(HAVE_GD_BMP,               1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageCreateFromTga,          [AC_DEFINE(HAVE_GD_TGA,               1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageStringFT,               [AC_DEFINE(HAVE_GD_FREETYPE,          1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdVersionString,               [AC_DEFINE(HAVE_GD_LIBVERSION,        1, [ ])], [], [ $GD_SHARED_LIBADD ])
+  PHP_CHECK_LIBRARY(gd, gdImageGetInterpolationMethod, [AC_DEFINE(HAVE_GD_GET_INTERPOLATION, 1, [ ])], [], [ $GD_SHARED_LIBADD ])
 ])
 
 dnl

ext/gd/config.w32

@@ -72,6 +72,7 @@ if (PHP_GD != "no") {
 /D HAVE_LIBPNG  \
 /D HAVE_XPM  \
 /D HAVE_COLORCLOSESTHWB  \
+/D HAVE_GD_GET_INTERPOLATION \
 /D USE_GD_IOCTX \
 /D MSWIN32 \
 		");

ext/gd/gd.c

@@ -294,6 +294,7 @@ static const zend_function_entry gd_functions[] = {
 	PHP_FE(imageaffine,								arginfo_imageaffine)
 	PHP_FE(imageaffinematrixconcat,					arginfo_imageaffinematrixconcat)
 	PHP_FE(imageaffinematrixget,					arginfo_imageaffinematrixget)
+	PHP_FE(imagegetinterpolation,					arginfo_imagegetinterpolation)
 	PHP_FE(imagesetinterpolation,					arginfo_imagesetinterpolation)
 	PHP_FE(imagesettile,							arginfo_imagesettile)
 	PHP_FE(imagesetbrush,							arginfo_imagesetbrush)
@@ -4100,6 +4101,26 @@ PHP_FUNCTION(imageaffinematrixconcat)
 	}
 } /* }}} */
 
+/* {{{ proto resource imagegetinterpolation(resource im)
+   Get the default interpolation method. */
+PHP_FUNCTION(imagegetinterpolation)
+{
+	zval *IM;
+	gdImagePtr im;
+
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "O", &IM, gd_image_ce) == FAILURE)  {
+		RETURN_THROWS();
+	}
+	im = php_gd_libgdimageptr_from_zval_p(IM);
+
+#ifdef HAVE_GD_GET_INTERPOLATION
+	RETURN_LONG(gdImageGetInterpolationMethod(im));
+#else
+	RETURN_LONG(im->interpolation_id);
+#endif
+}
+/* }}} */
+
 /* {{{ proto resource imagesetinterpolation(resource im [, int method]])
    Set the default interpolation method, passing -1 or 0 sets it to the libgd default (bilinear). */
 PHP_FUNCTION(imagesetinterpolation)

ext/gd/gd.stub.php

@@ -232,6 +232,8 @@ function imageaffinematrixget(int $type, $options = UNKNOWN): array|false {}
 
 function imageaffinematrixconcat(array $m1, array $m2): array|false {}
 
+function imagegetinterpolation(GdImage $im): int {}
+
 function imagesetinterpolation(GdImage $im, int $method = IMG_BILENEAR_FIXED): bool {}
 
 function imageresolution(GdImage $im, int $res_x = UNKNOWN, int $res_y = UNKNOWN): array|bool {}

ext/gd/gd_arginfo.h

@@ -556,6 +556,8 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_imageaffinematrixconcat, 0, 2, M
 	ZEND_ARG_TYPE_INFO(0, m2, IS_ARRAY, 0)
 ZEND_END_ARG_INFO()
 
+#define arginfo_imagegetinterpolation arginfo_imagecolorstotal
+
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_imagesetinterpolation, 0, 1, _IS_BOOL, 0)
 	ZEND_ARG_OBJ_INFO(0, im, GdImage, 0)
 	ZEND_ARG_TYPE_INFO(0, method, IS_LONG, 0)

ext/gd/libgd/gd_interpolation.c

@@ -2534,6 +2534,29 @@ int gdImageSetInterpolationMethod(gdImagePtr im, gdInterpolationMethod id)
 	return 1;
 }
 
+/**
+ * Function: gdImageGetInterpolationMethod
+ *
+ * Get the current interpolation method
+ *
+ * This is here so that the value can be read via a language or VM with an FFI
+ * but no (portable) way to extract the value from the struct.
+ *
+ * Parameters:
+ *   im - The image.
+ *
+ * Returns:
+ *   The current interpolation method.
+ *
+ * See also:
+ *   - <gdInterpolationMethod>
+ *   - <gdImageSetInterpolationMethod>
+ */
+gdInterpolationMethod gdImageGetInterpolationMethod(gdImagePtr im)
+{
+    return im->interpolation_id;
+}
+
 #ifdef _MSC_VER
 # pragma optimize("", on)
 #endif

ext/gd/php_gd.h

@@ -134,6 +134,7 @@ PHP_FUNCTION(imagescale);
 PHP_FUNCTION(imageaffine);
 PHP_FUNCTION(imageaffinematrixget);
 PHP_FUNCTION(imageaffinematrixconcat);
+PHP_FUNCTION(imagegetinterpolation);
 PHP_FUNCTION(imagesetinterpolation);
 
 PHP_FUNCTION(imagesetthickness);

ext/gd/tests/bug79068.phpt

@@ -6,16 +6,12 @@ if (!extension_loaded('gd')) die('skip gd extension not available');
 ?>
 --FILE--
 <?php
-require_once __DIR__ . '/func.inc';
-
 $src = imagecreatetruecolor(100, 100);
 imagefilledrectangle($src, 0, 0, 99, 99, 0xffffff);
 imageline($src, 10, 10, 90, 90, 0x000000);
 imagesetinterpolation($src, IMG_BSPLINE);
 imageaffine($src, [1, 1, 1, 1, 1, 1]);
-$dst = imagerotate($src, 80, 0xffffff);
-
-test_image_equals_file(__DIR__ . '/bug79068.png', $dst);
+var_dump(imagegetinterpolation($src) === IMG_BSPLINE);
 ?>
 --EXPECT--
-The images are equal.
+bool(true)

ext/gd/tests/imageinterpolation_basic.phpt

@@ -0,0 +1,59 @@
+--TEST--
+imagegetinterpolation() and imagesetinterpolation() basic test
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+$methods = array(
+	IMG_BELL,
+	IMG_BESSEL,
+	IMG_BILINEAR_FIXED,
+	IMG_BICUBIC,
+	IMG_BICUBIC_FIXED,
+	IMG_BLACKMAN,
+	IMG_BOX,
+	IMG_BSPLINE,
+	IMG_CATMULLROM,
+	IMG_GAUSSIAN,
+	IMG_GENERALIZED_CUBIC,
+	IMG_HERMITE,
+	IMG_HAMMING,
+	IMG_HANNING,
+	IMG_MITCHELL,
+	IMG_NEAREST_NEIGHBOUR,
+	IMG_POWER,
+	IMG_QUADRATIC,
+	IMG_SINC,
+	IMG_TRIANGLE,
+	IMG_WEIGHTED4,
+);
+$im = imagecreate(8, 8);
+foreach ($methods as $method) {
+	imagesetinterpolation($im, $method);
+	var_dump(imagegetinterpolation($im) === $method);
+}
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)