1916030 - Firefox fails to paint svg-as-an-image, if the svg element has a width or height of 0 and no viewBox

Status: NEW

(Core :: SVG, defect)

Description

[Daniel Holbert [:dholbert]]

Filing this as the underlying defect behind our WPT failure in bug 1906145.

Essentially, if an SVG image lacks a viewBox, and has a zero-sized width or height, then I think we synthesize a zero-sized viewBox from its width and height, and that means we don't paint anything when the image draws (because we scale up a zero-sized area to fill the image element's bounds, or something like that).

Other browsers do in fact paint in this case, though -- I suspect because they just decline to synthesize a viewBox from the SVG image's height and width, and they instead just use a viewBox based on the area that we're rendering to (the image element), or something along those lines.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: testcase 1 (<svg> has width=0)

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: testcase 2 (<svg> has height=0)

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: testcase 3 (<svg> has width and height both set to 0)

Comment 4

[Daniel Holbert [:dholbert]]

In all three testcases, we fail to paint the SVG in the top half of the testcase, whereas other engines reliably paint (when there's area to be painted).

Specifically:

• Firefox renders the top half with no cyan (i.e. not painting any content from the SVG image)
• Chromium renders the the top half with cyan backgrounds (for the img elements that are nonzero-sized).
• WebKit renders the top half with cyan backgrounds. (They also render all the img elements as being nonzero-sized, which disagrees with us and Chrome -- this sizing behavior is probably a WebKit bug).

Comment 5

[Daniel Holbert [:dholbert]]

When fixing this, I plan to include (possibly-evolved-a-bit) versions of those 3 testcases as WPTs, along with similar tests for <embed>, <svg:image>, SVG-as-a-background-image-with-background-size, etc. (in all cases having width and/or height set to 0 on the <svg> element, but nonzero width and/or height on the embedding context).