"Fix" sag scaling for hidpi

[Yuan Fu]

To get crisp images on hidpi displays, a common approach is to load an image 
double de dimension and rescale it down. E.g., load an 200x200 image and 
rescale it to 100x100. In Emacs this can be done by

(insert-image (create-image "200x200img.png" 'png nil :scale 0.5))

And Emacs will display a crisp 100x100 image in the buffer. However, this 
doesn’t work for sag images. If I do

(progn
  (require 'svg)
  (let ((svg (svg-create 200 200)))
    (svg-text svg "test"
              :font-size 100
              :y 150)
    (insert-image (svg-image svg :scale 0.5))))

The image is still blurry:

Turns out image.c resolves the dimension for svg images before generating them 
and skips rescaling all together. The following patch changes that behavior and 
allows me to generate crisp svg images:

WDYT?

Yuan

svg-scale.patch
Description: Binary data