[Emacs-diffs] master 857c5c2 2/2: Automatically scale images up on high-density screens

[Lars Ingebrigtsen]

branch: master
commit 857c5c24d6e57ac593e000198b644a0a88f54915
Author: Lars Ingebrigtsen <address@hidden>
Commit: Lars Ingebrigtsen <address@hidden>

    Automatically scale images up on high-density screens
    
    * doc/lispref/display.texi (ImageMagick Images): Mention :scale.
    (Defining Images): Mention image-scaling-factor.
    
    * lisp/image.el (image-compute-scaling-factor): New function
    (bug#22172).
    (create-image): Use it.
    (image-scaling-factor): New variable.
    
    * src/image.c (compute_image_size): Take :scale into account.
---
 doc/lispref/display.texi |   15 +++++++++++++++
 etc/NEWS                 |    5 +++++
 lisp/image.el            |   29 +++++++++++++++++++++++++++++
 src/image.c              |   15 +++++++++++++++
 4 files changed, 64 insertions(+), 0 deletions(-)

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 3238959..c8e7e4f 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5198,6 +5198,14 @@ and if @code{:height} is set it will have precedence over
 wish.  @code{:max-width} and @code{:max-height} will always preserve
 the aspect ratio.
 
address@hidden :scale @var{scale}
+This should be a number, where values higher than 1 means to increase
+the size, and lower means to decrease the size.  For instance, a value
+of 0.25 will make the image a quarter size of what it originally was.
+If the scaling makes the image larger than specified by
address@hidden:max-width} or @code{:max-height}, the resulting size will not
+exceed those two values.
+
 @item :format @var{type}
 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
@@ -5384,6 +5392,13 @@ Here is an example of using 
@code{image-load-path-for-library}:
 @end example
 @end defun
 
address@hidden image-scaling-factor
+Images are automatically scaled when created based on the
address@hidden variable.  The value is either a floating
+point number (where numbers higher than 1 means to increase the size
+and lower means to shrink the size), or the symbol @code{auto}, which
+will compute a scaling factor based on the font pixel size.
+
 @node Showing Images
 @subsection Showing Images
 @cindex show image
diff --git a/etc/NEWS b/etc/NEWS
index ad9a50c..fd56f0c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -769,6 +769,11 @@ longer warn about sending emails to top-level domains it 
hasn't heard
 about.
 
 +++
+** Images are automatically scaled before displaying based on the
+`image-scaling-factor' variable (if Emacs supports scaling the images
+in question).
+
++++
 ** In Show Paren Mode, a parenthesis can be highlighted when point
 stands inside it, and certain parens can be highlighted when point is
 at BOL or EOL, or in whitespace there.  To enable these, customize,
diff --git a/lisp/image.el b/lisp/image.el
index 663afa7..82a10a3 100644
--- a/lisp/image.el
+++ b/lisp/image.el
@@ -126,6 +126,18 @@ Subdirectories are not automatically included in the 
search."
   :type '(repeat (choice directory variable))
   :initialize 'custom-initialize-delay)
 
+(defcustom image-scaling-factor 'auto
+  "When displaying images, apply this scaling factor before displaying.
+This is not supported for all image types, and is mostly useful
+when you have a high-resolution monitor.
+The value is either a floating point number (where numbers higher
+than 1 means to increase the size and lower means to shrink the
+size), or the symbol `auto', which will compute a scaling factor
+based on the font pixel size."
+  :type '(choice number
+                 (const :tag "Automatically compute" auto))
+  :group 'image
+  :version "25.2")
 
 (defun image-load-path-for-library (library image &optional path no-error)
   "Return a suitable search path for images used by LIBRARY.
@@ -409,8 +421,25 @@ Image file names that are not absolute are searched for in 
the
   (setq type (image-type file-or-data type data-p))
   (when (image-type-available-p type)
     (append (list 'image :type type (if data-p :data :file) file-or-data)
+            (and (not (plist-get props :scale))
+                 (list :scale
+                       (image-compute-scaling-factor image-scaling-factor)))
            props)))
 
+(defun image-compute-scaling-factor (scaling)
+  (cond
+   ((numberp image-scaling-factor)
+    image-scaling-factor)
+   ((eq image-scaling-factor 'auto)
+    (let ((width (/ (float (window-width nil t)) (window-width))))
+      ;; If we assume that a typical character is 10 pixels in width,
+      ;; then we should scale all images according to how wide they
+      ;; are.  But don't scale images down.
+      (if (< width 10)
+          1
+        (/ (float width) 10))))
+   (t
+    (error "Invalid scaling factor %s" image-scaling-factor))))
 
 ;;;###autoload
 (defun put-image (image pos &optional string area)
diff --git a/src/image.c b/src/image.c
index 144fe30..bc5863f 100644
--- a/src/image.c
+++ b/src/image.c
@@ -8073,6 +8073,7 @@ compute_image_size (size_t width, size_t height,
 {
   Lisp_Object value;
   int desired_width, desired_height;
+  double scale = 1;
 
   /* If width and/or height is set in the display spec assume we want
      to scale to those values.  If either h or w is unspecified, the
@@ -8083,6 +8084,12 @@ compute_image_size (size_t width, size_t height,
   value = image_spec_value (spec, QCheight, NULL);
   desired_height = NATNUMP (value) ? min (XFASTINT (value), INT_MAX) : -1;
 
+  value = image_spec_value (spec, QCscale, NULL);
+  if (NATNUMP (value))
+    scale = extract_float (value);
+  width = width * scale;
+  height = height * scale;
+
   if (desired_width == -1)
     {
       value = image_spec_value (spec, QCmax_width, NULL);
@@ -8132,6 +8139,13 @@ compute_image_size (size_t width, size_t height,
     /* h known, calculate w.  */
     desired_width = scale_image_size (desired_height, height, width);
 
+  /* We have no width/height settings, so just apply the scale. */
+  if (desired_width == -1 && desired_height == -1)
+    {
+      desired_width = width;
+      desired_height = height;
+    }
+
   *d_width = desired_width;
   *d_height = desired_height;
 }
@@ -9795,6 +9809,7 @@ non-numeric, there is no explicit limit on the size of 
images.  */);
   DEFSYM (QCcrop, ":crop");
   DEFSYM (QCrotation, ":rotation");
   DEFSYM (QCmatrix, ":matrix");
+  DEFSYM (QCscale, ":scale");
   DEFSYM (QCcolor_adjustment, ":color-adjustment");
   DEFSYM (QCmask, ":mask");