Re: [PATCH] system: grub: Convert grub background using rsvg-convert

[Andy Wingo <wingo@igalia.com>]

On Fri 28 Aug 2015 19:15, Luis Felipe López Acevedo <felipe.lopez@openmailbox.org> writes:

> Modifying the document background does not affect the design at all,
> because we are using the dark rectangle on top of it as the background
> of the image, so it doesn't matter what the background of the document
> is.
>
> Could it be that rsvg-convert is complaining about transparency in the
> page/document background and not about the transparency of the
> checkerboard pattern in the "Background" layer? Because it is not
> complaining about the transparency in the layer that contains the logo
> (which has transparency as well), is it?

We could use guile-cairo / guile-rsvg to convert, fwiw.  Better to do
that than to cause our graphics people to modify the image.

  (use-modules (rsvg) (cairo))

  (define (->int x) (inexact->exact (ceiling x)))

  (define (render-to-png in-svg out-png)
    (let ((svg (rsvg-handle-new-from-file in-svg)))
      (call-with-values (lambda () (rsvg-handle-get-dimensions svg))
        (lambda (width height em ex)
          (let* ((surf (cairo-image-surface-create 'argb32
                                                   (->int width)
                                                   (->int height)))
                 (cr (cairo-create surf)))
            (rsvg-handle-render-cairo svg cr)
            (cairo-surface-flush surf)
            (cairo-surface-write-to-png (cairo-get-target cr) out-png))))))

That will render a png with the svg's natural pixel dimensions.  You can
use the png as is, or instead of rendering to a png you could use "surf"
as a source surface for other paint operations, for example if you want
to down-scale the image nicely.  Here's an example, for a suitable
definition of create-image-surface and scale-dimensions:

  (call-with-values (lambda () (create-image-surface filename width height))
    (lambda (surface swidth sheight)
      (if surface
          (call-with-values (lambda () (scale-dimensions (/ swidth 1.0 sheight)))
            (lambda (x0 y0 width height)
              (cairo-save cr)
              (cairo-translate cr x0 y0)
              (cairo-scale cr (/ width swidth) (/ height sheight))
              (cairo-set-source-surface cr surface 0 0)
              (cairo-pattern-set-filter (cairo-get-source cr) 'best)
              (cairo-rectangle cr 0 0 swidth sheight)
              (cairo-fill cr)
              (cairo-restore cr)
              (values width height)))
          (values 0 0))))

FWIW :)

Cheers,

Andy