Bug 6001 – CSS2: WebKit does not handle fallback custom cursors

• Component: CSS
• Status: RESOLVED FIXED

[Eric Seidel (no email)]

WebKit does not handle fallback custom cursors

I should have caught the fallback cursor issue when reviewing darin's orginal patch:
http://bugzilla.opendarwin.org/show_bug.cgi?id=5689

[Eric Seidel (no email)]

From the spec:
http://www.w3.org/TR/REC-CSS2/ui.html#cursor-props
"If the user agent cannot handle the first cursor of a list of cursors, it should attempt to handle the 
second, etc. If the user agent cannot handle any user-defined cursor, it must use the generic cursor at the 
end of the list."

[Eric Seidel (no email)]

http://www.w3.org/Graphics/SVG/Test/20030813/svggen/interact-cursor-01-f.svg
Demonstrates cursor fallback behavior.

http://www.w3.org/TR/css3-ui/
also has some example code.

[Darin Adler]

Even though I did the original custom cursor work, I suggest that someone else do the "list of cursors" and 
fallback machinery work.

[Alexey Proskuryakov]

Unless I'm missing something, this means that WebKit cannot handle any custom cursor specified in accordance with the spec, and also any custom cursor that WebKit handles is specified incorrectly.

[Eric Seidel (no email)]

I spoke with hyatt and darin this evening.  We've come up with a pretty simple fix for this.

1. We will need a new class, perhaps called CursorDescription. (like FontDescription).  This will contain CurorType enum (just like RenderStyle::cursor() does today), as well as a CachedImage* (just like cursorImage() does today), as well as a CursorDescription next pointer (CursorDescription* m_next; CursorDescription* next() const;)
2. RenderStyle::cursor() will stay (to optimize for the common single-specified cursor case).  RenderStyle::cursorImage() will change to CursorDescription* RenderStyle::cursorList().
3. Either cursor() will return a special CURSOR_LIST enum value, or simply cursorList() returning non-null will trigger the cursor list fallback behavior instead of the normal single-cursor case.

That's pretty much it.  This should be a pretty small patch and shouldn't take more than a couple hours to code up.

[Alexey Proskuryakov]

There's a lot work already done in an unfinished patch for bug 6002.

[Eric Seidel (no email)]

One other thing I forgot.  The CursorDescription class can't just point to a CacheImage, as the cursor might not just be an image.  It will need to point to either an SVGCursorElement (bug 6002) or a CachedImage, FloatPoint (hotspot -- as part of CSS3) pair.  Perhaps we'll want an abstract class to codify this CursorProvider interface.  Not sure.

[Eric Seidel (no email)]

Fixed as part of bug 6002