Implement :max-width/:max-height for (ImageMagic) images

* doc/lispref/display.texi (ImageMagick Images): Mention :max-width and
:max-height.

* lisp/net/shr.el (shr-rescale-image): Use the new
:max-width/:max-height functionality.

* src/image.c (compute_image_size): New function to implement
:max-width and :max-height.
(imagemagick_load_image): Use it.

2 files changed, 14 insertions, 0 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index c00d3392908..e95010a11a9 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2013-06-23  Lars Magne Ingebrigtsen  <larsi@gnus.org>
+
+        * display.texi (ImageMagick Images): Mention :max-width and
+        :max-height.
+
 2013-06-20  Paul Eggert  <eggert@cs.ucla.edu>
 
         * numbers.texi (Math Functions): Remove obsolete function log10.
diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 34eda6ecd6f..d82b9a4c5a2 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -4653,6 +4653,15 @@ image.  If only one of them is specified, the other one will be
 calculated so as to preserve the aspect ratio.  If both are specified,
 aspect ratio may not be preserved.
 
+@item :max-width, :max-height
+The @code{:max-width} and @code{:max-height} keywords are used for
+scaling if the size of the image of the image exceeds these values.
+If @code{:width} is set it will have presedence over @code{max-width},
+and if @code{:height} is set it will have presedence over
+@code{max-height}, but you can otherwise mix these keywords as you
+wish.  @code{:max-width} and @code{:max-height} will always preserve
+the aspec ratio.
+
 @item :rotation
 Specifies a rotation angle in degrees.