Support native image transforms on MS-Windows

This changeset also rearranges native image transform code
for other platforms to make it cleaner, and also removes
the support for native cropping.  For the discussions, see
https://lists.gnu.org/archive/html/emacs-devel/2019-06/msg00242.html

* src/w32term.c (w32_image_rotations_p, transform): New functions.
(w32_draw_image_foreground): If image rotation is requested
and supported, call PlgBlt to transform the image.
(w32_initialize): Populate the PlgBlt function pointer if it
is supported.
* src/w32term.h (w32_image_rotations_p): Add prototype.
* src/dispextern.h (struct image) [HAVE_NTGUI]: New member xform.
* src/image.c (compute_image_rotation): Renamed from
image_set_rotation.  Only compute and returns the rotation
angle; leave the matrix calculation for later.  Log an error
message if the :rotation parameter is not a number.
(image_set_crop): Function deleted.  We no longer support
native cropping, as one can display an image slice instead.
(image_set_transform): Compute the transform matrix in its
entirety here, in two variants: one for XRender and Cairo, the
other for NS and MS-Windows.  call compute_image_size and
compute_image_rotation internally.
(lookup_image) [HAVE_NATIVE_TRANSFORMS]: Call only
image_set_transform.  No need to pass the transform matrix to
image_set_transform.
(Fimage_transforms_p): Return a list of transform capabilities
rather than a simple boolean.  Support TTY frames as well.
* src/nsimage.m (setTransform:): Don't invert the matrix, as
it is already inverted in image.c.

* test/manual/image-transforms-tests.el (test-cropping): State
in the text that only ImageMagick supports cropping.

* doc/lispref/display.texi (Image Descriptors): Update the
documentation of native image transforms.
(ImageMagick Images): Move the description of ':crop' here.

* etc/NEWS: Minor copyedits of the feature announcement.

1 files changed, 37 insertions, 23 deletions

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 217df3b2cc2..c95f2df0fb8 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5188,24 +5188,6 @@ values.  If both @code{:scale} and @code{:height}/@code{:width} are
 specified, the height/width will be adjusted by the specified scaling
 factor.
 
-@item :crop @var{geometry}
-This should be a list of the form @code{(@var{width} @var{height}
-@var{x} @var{y})}.  @var{width} and @var{height} specify the width
-and height of the cropped image.  If @var{x} is a positive number it
-specifies the offset of the cropped area from the left of the original
-image, and if negative the offset from the right.  If @var{y} is a
-positive number it specifies the offset from the top of the original
-image, and if negative from the bottom.  If @var{x} or @var{y} are
-@code{nil} or unspecified the crop area will be centred on the
-original image.
-
-If the crop area is outside or overlaps the edge of the image it will
-be reduced to exclude any areas outside of the image.  This means it
-is not possible to use @code{:crop} to increase the size of the image
-by entering large @var{width} or @var{height} values.
-
-Cropping is performed after scaling but before rotation.
-
 @item :rotation @var{angle}
 Specifies a rotation angle in degrees.  Only multiples of 90 degrees
 are supported, unless the image type is @code{imagemagick}.  Positive
@@ -5355,16 +5337,30 @@ This function returns @code{t} if image @var{spec} has a mask bitmap.
 @end defun
 
 @defun image-transforms-p &optional frame
-This function returns @code{t} if @var{frame} supports image scaling
-and rotation.  @var{frame} @code{nil} or omitted means to use the
-selected frame (@pxref{Input Focus}).
+This function returns non-@code{nil} if @var{frame} supports image
+scaling and rotation.  @var{frame} @code{nil} or omitted means to use
+the selected frame (@pxref{Input Focus}).  The returned list includes
+symbols that indicate which image transform operations are supported:
+
+@table @code
+@item scale
+Image scaling is supported by @var{frame} via the @code{:scale},
+@code{:width}, @code{:height}, @code{:max-width}, and
+@code{:max-height} properties.
+@item rotate90
+Image rotation is supported by @var{frame} if the rotation angle is an
+integral multiple of 90 degrees.
+@item rotate
+Image rotation by arbitrary angles is supported by @var{frame}.
+@item crop
+Image cropping is supported by @var{frame}.
+@end table
 
-If image transforms are not supported, @code{:rotation},
+If image transforms are not supported, @code{:rotation}, @code{:crop},
 @code{:width}, @code{:height}, @code{:scale}, @code{:max-width} and
 @code{:max-height} will only be usable through ImageMagick, if
 available (@pxref{ImageMagick Images}).
 @end defun
-
 @node XBM Images
 @subsection XBM Images
 @cindex XBM
@@ -5506,6 +5502,24 @@ The value, @var{type}, should be a symbol specifying the type of the
 image data, as found in @code{image-format-suffixes}.  This is used
 when the image does not have an associated file name, to provide a
 hint to ImageMagick to help it detect the image type.
+
+@item :crop @var{geometry}
+The value of @var{geometry} should be a list of the form
+@code{(@var{width} @var{height} @var{x} @var{y})}.  @var{width} and
+@var{height} specify the width and height of the cropped image.  If
+@var{x} is a positive number it specifies the offset of the cropped
+area from the left of the original image, and if negative the offset
+from the right.  If @var{y} is a positive number it specifies the
+offset from the top of the original image, and if negative from the
+bottom.  If @var{x} or @var{y} are @code{nil} or unspecified the crop
+area will be centred on the original image.
+
+If the crop area is outside or overlaps the edge of the image it will
+be reduced to exclude any areas outside of the image.  This means it
+is not possible to use @code{:crop} to increase the size of the image
+by entering large @var{width} or @var{height} values.
+
+Cropping is performed after scaling but before rotation.
 @end table
 
 @node SVG Images