[css3-images] comments on radial gradients from Tab Atkins Jr. on 2012-03-14 (www-style@w3.org from March 2012) (original) (raw)

On Wed, Mar 14, 2012 at 3:38 PM, L. David Baron <dbaron@dbaron.org> wrote:

On Wednesday 2012-03-14 15:07 -0700, Tab Atkins Jr. wrote:

In section 4.3 (Repeating gradients), http://dev.w3.org/csswg/css3-images/#repeating-gradients :

I think this section ought to be clearer about how negative color stops are handled for repeating radial gradients. The rules for repeating in this section seem to contradict the earlier statement that positions less than 0 have no effect on rendering in radial gradients, since direct application of the repeating rules seems to make them take up space and render.

Why isn't this handled by the existing text? "When rendered, however, the color-stops are repeated infinitely in both directions, with their positions shifted by multiples of the difference between the last specified color-stop's position and the first specified color-stop's position."

I can't even tell from that which behavior you're saying happens. Given:

background: repeating-radial-gradient(red -50%, green 0%, blue 100%)

Does the red->green part show up or not? The radial gradients section explicitly says that it doesn't, and the repeating gradients section explicitly says that it does.

I suspect the problem is in my wording, where it's potentially ambiguous whether I'm referring to "the location of a color-stop" or "a location on the gradient line".

The "negative locations aren't rendered" thing is referring to the latter. Color-stops themselves aren't things to be rendered; all they do is affect the color of the gradient line, which is then used for rendering.

In the radial-gradient section, I've made the following change to try to make this clearer:

Old

Negative locations can be specified; though negative locations are never directly consulted for rendering, they can affect the color of non-negative locations on the gradient ray through interpolation.

New

A color-stop can be placed at a negative location; though the

negative region of the gradient ray is never directly consulted for rendering, color stops placed there can affect the color of non-negative locations on the gradient ray through interpolation.

Does this help? Hopefully it's now clear that the "not consulted for rendering" bit is exclusively talking about the gradient line, not the color-stops.

~TJ

Received on Wednesday, 14 March 2012 22:53:35 UTC