Don't show the broken image icon for missing CSS images

[Simon Fraser (smfr)]

We currently render the broken image icon for missing CSS images (backgrounds, border-image etc) but I don't think we should. I think we should only show it for content images.

[Said Abou-Hallawa]

(In reply to Simon Fraser (smfr) from comment #0)
> We currently render the broken image icon for missing CSS images
> (backgrounds, border-image etc) but I don't think we should. I think we
> should only show it for content images.

How can this happen? Can you include a test case?

In RenderBoxModelObject::paintFillLayerExtended() we check:

bool shouldPaintBackgroundImage = bgImage && bgImage->canRender(this, style().effectiveZoom());

If the image is missing, bgImage will be null. And if an error happens while loading or decoding the image, bgImage->canRender() will return false. In both cases drawing the background image step will be skipped.

[Simon Fraser (smfr)]

I think I was seeing this for border-image.

[Sam Sneddon [:gsnedders]]

*** Bug 231078 has been marked as a duplicate of this bug. ***

[Sam Sneddon [:gsnedders]]

(In reply to Simon Fraser (smfr) from comment #2)
> I think I was seeing this for border-image.

Bug 206909 was caused by us rendering `content: -webkit-image-set(url(...))` given an invalid image.

[Sam Sneddon [:gsnedders]]

<rdar://problem/82999675>

[Simon Fraser (smfr)]

I can't figure out how to reproduce this now.

[Simon Fraser (smfr)]

This is one way:
            background-image: -webkit-cross-fade(url('http://www.example.com/broken.png'), url('http://www.example.com/broken.png'), 50%);

I think it's bad that CachedImage::image() and CachedImage::imageForRenderer() can return the broken image icon. That causes hilarity like consulting this image for it's opaqueness, or EXIF orientation, even if it's never used in this context (e.g. CSS backgrounds).

[Simon Fraser (smfr)]

Created attachment 441689 [details]
Some examples

[Sam Sneddon [:gsnedders]]

(In reply to Simon Fraser (smfr) from comment #6)
> I can't figure out how to reproduce this now.

content: -webkit-image-set(url('http://www.example.com/broken.png') 1x); still suffices too

should really go through and add a whole bunch of WPT tests for this, in the various places where <image> is used as the value

[Sam Sneddon [:gsnedders]]

<rdar://problem/84026868>

[Ryan Reno]

The images level 4 spec introduced the concept of an invalid image: http://w3c.github.io/csswg-drafts/css-images-4/#invalid-image

I implemented this as a StyleInvalidImage for use in image-set in 261015@main Maybe this is useful in the contexts described in this bug too?