Merge pull request #3406 from Nazime/negativeindex

Add negative index to PixelAccess

Tests/test_image_access.py

@@ -64,6 +64,43 @@ class TestImagePutPixel(AccessTest):
 
         self.assert_image_equal(im1, im2)
 
+    def test_sanity_negative_index(self):
+        im1 = hopper()
+        im2 = Image.new(im1.mode, im1.size, 0)
+
+        width, height = im1.size
+        self.assertEqual(im1.getpixel((0, 0)), im1.getpixel((-width, -height)))
+        self.assertEqual(im1.getpixel((-1, -1)),
+                         im1.getpixel((width-1, height-1)))
+
+        for y in range(-1, -im1.size[1]-1, -1):
+            for x in range(-1, -im1.size[0]-1, -1):
+                pos = x, y
+                im2.putpixel(pos, im1.getpixel(pos))
+
+        self.assert_image_equal(im1, im2)
+
+        im2 = Image.new(im1.mode, im1.size, 0)
+        im2.readonly = 1
+
+        for y in range(-1, -im1.size[1]-1, -1):
+            for x in range(-1, -im1.size[0]-1, -1):
+                pos = x, y
+                im2.putpixel(pos, im1.getpixel(pos))
+
+        self.assertFalse(im2.readonly)
+        self.assert_image_equal(im1, im2)
+
+        im2 = Image.new(im1.mode, im1.size, 0)
+
+        pix1 = im1.load()
+        pix2 = im2.load()
+
+        for y in range(-1, -im1.size[1]-1, -1):
+            for x in range(-1, -im1.size[0]-1, -1):
+                pix2[x, y] = pix1[x, y]
+
+        self.assert_image_equal(im1, im2)
 
 class TestImageGetPixel(AccessTest):
     @staticmethod
@@ -85,23 +122,43 @@ class TestImageGetPixel(AccessTest):
             im.getpixel((0, 0)), c,
             "put/getpixel roundtrip failed for mode %s, color %s" % (mode, c))
 
+        # check putpixel negative index
+        im.putpixel((-1, -1), c)
+        self.assertEqual(
+            im.getpixel((-1, -1)), c,
+            "put/getpixel roundtrip negative index failed"
+            " for mode %s, color %s" % (mode, c))
+
         # Check 0
         im = Image.new(mode, (0, 0), None)
         with self.assertRaises(IndexError):
             im.putpixel((0, 0), c)
         with self.assertRaises(IndexError):
             im.getpixel((0, 0))
+        # Check 0 negative index
+        with self.assertRaises(IndexError):
+            im.putpixel((-1, -1), c)
+        with self.assertRaises(IndexError):
+            im.getpixel((-1, -1))
 
         # check initial color
         im = Image.new(mode, (1, 1), c)
         self.assertEqual(
             im.getpixel((0, 0)), c,
             "initial color failed for mode %s, color %s " % (mode, c))
+        # check initial color negative index
+        self.assertEqual(
+            im.getpixel((-1, -1)), c,
+            "initial color failed with negative index"
+            "for mode %s, color %s " % (mode, c))
 
         # Check 0
         im = Image.new(mode, (0, 0), c)
         with self.assertRaises(IndexError):
             im.getpixel((0, 0))
+        # Check 0 negative index
+        with self.assertRaises(IndexError):
+            im.getpixel((-1, -1))
 
     def test_basic(self):
         for mode in ("1", "L", "LA", "I", "I;16", "I;16B", "F",

src/PIL/PyAccess.py

@@ -74,7 +74,12 @@ class PyAccess(object):
         """
         if self.readonly:
             raise ValueError('Attempt to putpixel a read only image')
-        (x, y) = self.check_xy(xy)
+        (x, y) = xy
+        if x < 0:
+            x = self.xsize + x
+        if y < 0:
+            y = self.ysize + y
+        (x, y) = self.check_xy((x, y))
         return self.set_pixel(x, y, color)
 
     def __getitem__(self, xy):
@@ -88,8 +93,12 @@ class PyAccess(object):
         :returns: a pixel value for single band images, a tuple of
           pixel values for multiband images.
         """
-
-        (x, y) = self.check_xy(xy)
+        (x, y) = xy
+        if x < 0:
+            x = self.xsize + x
+        if y < 0:
+            y = self.ysize + y
+        (x, y) = self.check_xy((x, y))
         return self.get_pixel(x, y)
 
     putpixel = __setitem__

src/_imaging.c

@@ -472,6 +472,13 @@ getpixel(Imaging im, ImagingAccess access, int x, int y)
       FLOAT32 f;
     } pixel;
 
+    if (x < 0) {
+        x = im->xsize + x;
+    }
+    if (y < 0) {
+        y = im->ysize + y;
+    }
+
     if (x < 0 || x >= im->xsize || y < 0 || y >= im->ysize) {
         PyErr_SetString(PyExc_IndexError, outside_image);
         return NULL;
@@ -1649,6 +1656,13 @@ _putpixel(ImagingObject* self, PyObject* args)
 
     im = self->image;
 
+    if (x < 0) {
+        x = im->xsize + x;
+    }
+    if (y < 0) {
+        y = im->ysize + y;
+    }
+
     if (x < 0 || x >= im->xsize || y < 0 || y >= im->ysize) {
         PyErr_SetString(PyExc_IndexError, outside_image);
         return NULL;
@@ -3014,6 +3028,13 @@ pixel_access_setitem(PixelAccessObject *self, PyObject *xy, PyObject *color)
     if (_getxy(xy, &x, &y))
         return -1;
 
+    if (x < 0) {
+        x = im->xsize + x;
+    }
+    if (y < 0) {
+        y = im->ysize + y;
+    }
+
     if (x < 0 || x >= im->xsize || y < 0 || y >= im->ysize) {
         PyErr_SetString(PyExc_IndexError, outside_image);
         return -1;