images need be fetched via ResourceTask

[servo]

images need be fetched via ResourceTask

[BrendanEich]

We do want to avoid loading images that are not presented, though -- see https://bugzilla.mozilla.org/show_bug.cgi?id=689623.

/be

[pcwalton]

There are a couple of things to note here:

• Sometimes, only layout can determine whether an image is going to be
  displayed at all. This is the case for the CSS background-image property,
  for example.
• Layout needs to be in charge of loading the images, because we don't want
  to decode an image until it's visible. Gecko made the mistake of decoding
  images immediately regardless of their visibility, and it's the source of a
  lot of complaints about Firefox's memory usage. Let's make sure we do this
  right in Servo.
  On Jul 28, 2012 5:04 PM, "Brian Anderson" <
  [email protected]>
  wrote:

images are loaded by apply_style directly from disk. In order to use the
resource manager to load the image we need to know the url of the current
document (in order to resolve relative paths), and that url isn't available
to the layout task currently.

It seems like layout shouldn't be responsible for loading images anyway,
so something needs to be reconsidered here.

---

Reply to this email directly or view it on GitHub:
#35

[bzbarsky]

Note that for background-image the relevant base URI is the base URI of the stylesheet, not of the document (though the two may happen to be equal). So really, only someone who knows what the source of the image is can possibly know what base URI to use for it.

A separate discussion to be had is how we want to represent URIs in servo....

[brson]

OK, I've written an image cache task, with two operations, Prefetch and GetImage, and I've hooked it up to layout, so now images are being loaded through the resource manager.

Right now what happens is that when layout applies a background image style it sends the Prefetch message, at which point the image cache will tell the resource manager to begin loading the file.

Later on, when building the display list, we post the GetImage method, wait for the result and store the image in the display list. It's not until GetImage that the image cache actually does the decoding. Because we wait for the image, we are still doing decoding sequentially. What we really want is to store a future in the display list, but I need to rewrite the futures module for that.

The burrito kitty test works when loading from a local file, but when loading from the network the image doesn't arrive in time so it doesn't display. We'll need to post a reflow message in this case.