implement text anchor for truetype fonts

(cherry picked from commit bac9025918ccf944bac77addc130f33cf9d74701)

docs/reference/ImageDraw.rst

@@ -74,6 +74,61 @@ To load a OpenType/TrueType font, use the truetype function in the
 :py:mod:`~PIL.ImageFont` module. Note that this function depends on third-party
 libraries, and may not available in all PIL builds.
 
+Text anchors
+^^^^^^^^^^^^
+
+The ``anchor`` parameter determines the position of the ``xy`` coordinates relative to the text.
+It consists of two characters, the horizontal and vertical alignment.
+
+The default value is ``la`` for horizontal text and ``lt`` for vertical text.
+
+This parameter is ignored for legacy PIL fonts, where the anchor is always top-left.
+
++---+-----------------------+-------------------------------------------------------+
+|                            Horizontal anchor alignment                            |
++===+=======================+=======================================================+
+| l | left                  | Anchor is to the left of the text.                    |
++---+-----------------------+-------------------------------------------------------+
+| m | middle                | Anchor is horizontally centered with the text.        |
++---+-----------------------+-------------------------------------------------------+
+| r | right                 | Anchor is to the right of the text.                   |
++---+-----------------------+-------------------------------------------------------+
+| s | baseline              | **(vertical text only)**                              |
+|   |                       | Anchor is at the baseline (middle) of the text.       |
+|   |                       | The exact alignment depends on the font.              |
++---+-----------------------+-------------------------------------------------------+
+
++---+-----------------------+-------------------------------------------------------+
+|                           Vertical anchor alignment                               |
++===+=======================+=======================================================+
+| a | ascender (top)        | **(horizontal text only)**                            |
+|   |                       | Anchor is at the ascender line (top)                  |
+|   |                       | of the first line of text.                            |
++---+-----------------------+-------------------------------------------------------+
+| t | top                   | **(single-line text only)**                           |
+|   |                       | Anchor is at the top of the text.                     |
++---+-----------------------+-------------------------------------------------------+
+| m | middle                | Anchor is vertically centered with the text.          |
+|   |                       | For horizontal text this is the midpoint of the       |
+|   |                       | first ascender line and the last descender line.      |
++---+-----------------------+-------------------------------------------------------+
+| s | baseline              | **(horizontal text only)**                            |
+|   |                       | Anchor is at the baseline (bottom)                    |
+|   |                       | of the first line of text, only                       |
+|   |                       | descenders extend below the anchor.                   |
++---+-----------------------+-------------------------------------------------------+
+| b | bottom                | **(single-line text only)**                           |
+|   |                       | Anchor is at the bottom of the text.                  |
++---+-----------------------+-------------------------------------------------------+
+| d | descender (bottom)    | **(horizontal text only)**                            |
+|   |                       | Anchor is at the descender line (bottom)              |
+|   |                       | of the last line of text.                             |
++---+-----------------------+-------------------------------------------------------+
+
+See `Font metrics on Wikipedia <https://en.wikipedia.org/wiki/Typeface#Font_metrics>`_
+for more information on the specific terms used.
+
+
 Example: Draw Partial Opacity Text
 ----------------------------------
 
@@ -295,18 +350,27 @@ Methods
 
     Draws the string at the given position.
 
-    :param xy: Top left corner of the text.
+    :param xy: The anchor coordinates of the text.
     :param text: Text to be drawn. If it contains any newline characters,
                  the text is passed on to
                  :py:meth:`~PIL.ImageDraw.ImageDraw.multiline_text`.
     :param fill: Color to use for the text.
     :param font: An :py:class:`~PIL.ImageFont.ImageFont` instance.
+    :param anchor: The text anchor alignment. Determines the relative location of
+                   the anchor to the text. The default alignment is top left.
+                   See :ref:`Text anchors` for valid values. This parameter is
+                   ignored for legacy PIL fonts.
+
+                    .. note:: This parameter was present in earlier versions
+                              of Pillow, but implemented only in version 7.2.0.
+
     :param spacing: If the text is passed on to
                     :py:meth:`~PIL.ImageDraw.ImageDraw.multiline_text`,
                     the number of pixels between lines.
     :param align: If the text is passed on to
                   :py:meth:`~PIL.ImageDraw.ImageDraw.multiline_text`,
-                  ``"left"``, ``"center"`` or ``"right"``.
+                  ``"left"``, ``"center"`` or ``"right"``. Determines the relative alignment of lines.
+                  Use the ``anchor`` parameter to specify the alignment to ``xy``.
     :param direction: Direction of the text. It can be ``"rtl"`` (right to
                       left), ``"ltr"`` (left to right) or ``"ttb"`` (top to bottom).
                       Requires libraqm.
@@ -347,12 +411,22 @@ Methods
 
     Draws the string at the given position.
 
-    :param xy: Top left corner of the text.
+    :param xy: The anchor coordinates of the text.
     :param text: Text to be drawn.
     :param fill: Color to use for the text.
     :param font: An :py:class:`~PIL.ImageFont.ImageFont` instance.
+
+    :param anchor: The text anchor alignment. Determines the relative location of
+                   the anchor to the text. The default alignment is top left.
+                   See :ref:`Text anchors` for valid values. This parameter is
+                   ignored for legacy PIL fonts.
+
+                    .. note:: This parameter was present in earlier versions
+                              of Pillow, but implemented only in version 7.2.0.
+
     :param spacing: The number of pixels between lines.
-    :param align: ``"left"``, ``"center"`` or ``"right"``.
+    :param align: ``"left"``, ``"center"`` or ``"right"``. Determines the relative alignment of lines.
+                  Use the ``anchor`` parameter to specify the alignment to ``xy``.
     :param direction: Direction of the text. It can be ``"rtl"`` (right to
                       left), ``"ltr"`` (left to right) or ``"ttb"`` (top to bottom).
                       Requires libraqm.

src/PIL/ImageDraw.py

@@ -320,6 +320,7 @@ class ImageDraw:
                     features=features,
                     language=language,
                     stroke_width=stroke_width,
+                    anchor=anchor,
                     *args,
                     **kwargs,
                 )
@@ -333,6 +334,7 @@ class ImageDraw:
                         features,
                         language,
                         stroke_width,
+                        anchor,
                         *args,
                         **kwargs,
                     )
@@ -353,7 +355,7 @@ class ImageDraw:
                 draw_text(stroke_ink, stroke_width)
 
                 # Draw normal text
-                draw_text(ink, 0, (stroke_width, stroke_width))
+                draw_text(ink, 0)
             else:
                 # Only draw normal text
                 draw_text(ink)
@@ -373,6 +375,16 @@ class ImageDraw:
         stroke_width=0,
         stroke_fill=None,
     ):
+        if direction == "ttb":
+            raise ValueError("ttb direction is unsupported for multiline text")
+
+        if anchor is None:
+            anchor = "la"
+        elif len(anchor) != 2:
+            raise ValueError("anchor must be a 2 character string")
+        elif anchor[1] in "tb":
+            raise ValueError("anchor not supported for multiline text")
+
         widths = []
         max_width = 0
         lines = self._multiline_split(text)
@@ -390,16 +402,33 @@ class ImageDraw:
             )
             widths.append(line_width)
             max_width = max(max_width, line_width)
-        left, top = xy
+
+        top = xy[1]
+        if anchor[1] == "m":
+            top -= (len(lines) - 1) * line_spacing / 2.0
+        elif anchor[1] == "d":
+            top -= (len(lines) - 1) * line_spacing
+
         for idx, line in enumerate(lines):
+            left = xy[0]
+            width_difference = max_width - widths[idx]
+
+            # first align left by anchor
+            if anchor[0] == "m":
+                left -= width_difference / 2.0
+            elif anchor[0] == "r":
+                left -= width_difference
+
+            # then align by align parameter
             if align == "left":
-                pass  # left = x
+                pass
             elif align == "center":
-                left += (max_width - widths[idx]) / 2.0
+                left += width_difference / 2.0
             elif align == "right":
-                left += max_width - widths[idx]
+                left += width_difference
             else:
                 raise ValueError('align must be "left", "center" or "right"')
+
             self.text(
                 (left, top),
                 line,
@@ -413,7 +442,6 @@ class ImageDraw:
                 stroke_fill=stroke_fill,
             )
             top += line_spacing
-            left = xy[0]
 
     def textsize(
         self,

src/PIL/ImageFont.py

@@ -347,6 +347,7 @@ class FreeTypeFont:
         features=None,
         language=None,
         stroke_width=0,
+        anchor=None,
     ):
         """
         Create a bitmap for the text.
@@ -395,6 +396,12 @@ class FreeTypeFont:
 
                          .. versionadded:: 6.2.0
 
+        :param anchor:  The text anchor alignment. Determines the relative location of
+                        the anchor to the text. The default alignment is top left.
+                        See :ref:`Text anchors` for valid values.
+
+                         .. versionadded:: 8.0.0
+
         :return: An internal PIL storage memory instance as defined by the
                  :py:mod:`PIL.Image.core` interface module.
         """
@@ -405,6 +412,7 @@ class FreeTypeFont:
             features=features,
             language=language,
             stroke_width=stroke_width,
+            anchor=anchor,
         )[0]
 
     def getmask2(
@@ -416,6 +424,7 @@ class FreeTypeFont:
         features=None,
         language=None,
         stroke_width=0,
+        anchor=None,
         *args,
         **kwargs,
     ):
@@ -466,14 +475,21 @@ class FreeTypeFont:
 
                          .. versionadded:: 6.2.0
 
+        :param anchor:  The text anchor alignment. Determines the relative location of
+                        the anchor to the text. The default alignment is top left.
+                        See :ref:`Text anchors` for valid values.
+
+                         .. versionadded:: 8.0.0
+
         :return: A tuple of an internal PIL storage memory instance as defined by the
                  :py:mod:`PIL.Image.core` interface module, and the text offset, the
                  gap between the starting coordinate and the first marking
         """
         size, offset = self.font.getsize(
-            text, mode == "1", direction, features, language
+            text, mode == "1", direction, features, language, anchor
         )
         size = size[0] + stroke_width * 2, size[1] + stroke_width * 2
+        offset = offset[0] - stroke_width, offset[1] - stroke_width
         im = fill("L", size, 0)
         self.font.render(
             text, im.id, mode == "1", direction, features, language, stroke_width

src/_imagingft.c

@@ -626,17 +626,25 @@ font_getsize(FontObject* self, PyObject* args)
     int mask = 0; /* is FT_LOAD_TARGET_MONO enabled? */
     const char *dir = NULL;
     const char *lang = NULL;
+    const char *anchor = NULL;
     PyObject *features = Py_None;
     PyObject *string;
 
     /* calculate size and bearing for a given string */
 
-    if (!PyArg_ParseTuple(args, "O|izOz:getsize", &string, &mask, &dir, &features, &lang)) {
+    if (!PyArg_ParseTuple(args, "O|izOzz:getsize", &string, &mask, &dir, &features, &lang, &anchor)) {
         return NULL;
     }
 
     horizontal_dir = dir && strcmp(dir, "ttb") == 0 ? 0 : 1;
 
+    if (anchor == NULL) {
+        anchor = horizontal_dir ? "la" : "lt";
+    }
+    if (strlen(anchor) != 2) {
+        goto bad_anchor;
+    }
+
     count = text_layout(string, self, dir, features, lang, &glyph_info, mask);
     if (PyErr_Occurred()) {
         return NULL;
@@ -720,11 +728,75 @@ font_getsize(FontObject* self, PyObject* args)
     x_anchor = y_anchor = 0;
     if (face) {
         if (horizontal_dir) {
-            x_anchor = 0;
+            switch (anchor[0]) {
-            y_anchor = PIXEL(self->face->size->metrics.ascender);
+            case 'l':  // left
+                x_anchor = 0;
+                break;
+            case 'm':  // middle (left + right) / 2
+                x_anchor = PIXEL(position / 2);
+                break;
+            case 'r':  // right
+                x_anchor = PIXEL(position);
+                break;
+            case 's':  // vertical baseline
+            default:
+                goto bad_anchor;
+            }
+            switch (anchor[1]) {
+            case 'a':  // ascender
+                y_anchor = PIXEL(self->face->size->metrics.ascender);
+                break;
+            case 't':  // top
+                y_anchor = y_max;
+                break;
+            case 'm':  // middle (ascender + descender) / 2
+                y_anchor = PIXEL((self->face->size->metrics.ascender + self->face->size->metrics.descender) / 2);
+                break;
+            case 's':  // horizontal baseline
+                y_anchor = 0;
+                break;
+            case 'b':  // bottom
+                y_anchor = y_min;
+                break;
+            case 'd':  // descender
+                y_anchor = PIXEL(self->face->size->metrics.descender);
+                break;
+            default:
+                goto bad_anchor;
+            }
         } else {
-            x_anchor = x_min;
+            switch (anchor[0]) {
-            y_anchor = 0;
+            case 'l':  // left
+                x_anchor = x_min;
+                break;
+            case 'm':  // middle (left + right) / 2
+                x_anchor = (x_min + x_max) / 2;
+                break;
+            case 'r':  // right
+                x_anchor = x_max;
+                break;
+            case 's':  // vertical baseline
+                x_anchor = 0;
+                break;
+            default:
+                goto bad_anchor;
+            }
+            switch (anchor[1]) {
+            case 't':  // top
+                y_anchor = 0;
+                break;
+            case 'm':  // middle (top + bottom) / 2
+                y_anchor = PIXEL(position / 2);
+                break;
+            case 'b':  // bottom
+                y_anchor = PIXEL(position);
+                break;
+            case 'a':  // ascender
+            case 's':  // horizontal baseline
+            case 'd':  // descender
+            default:
+                goto bad_anchor;
+            }
         }
     }
 
@@ -733,6 +805,10 @@ font_getsize(FontObject* self, PyObject* args)
         (x_max - x_min), (y_max - y_min),
         (-x_anchor + x_min), -(-y_anchor + y_max)
     );
+
+bad_anchor:
+    PyErr_Format(PyExc_ValueError, "bad anchor specified: %s", anchor);
+    return NULL;
 }
 
 static PyObject*