845985 - SVG Filters: feComponentTransfer type=discrete treats single-valued arrays incorrectly

Status: RESOLVED FIXED

(Core :: SVG, defect)

Description

[Michael Mullany]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_5) AppleWebKit/536.26.17 (KHTML, like Gecko) Version/6.0.2 Safari/536.26.17

Steps to reproduce:

Created an SVG filter with a single value in the array for an feComponentTransfer.


Actual results:

The filter failed to convert the input values to the value contained in the array, and instead ignores the component transfer.


Expected results:

The spec says - for an input value C, where C<1, and an input array of [V0...Vn-1] find an index k where k/n <= C < (k+1)/n. C' (the output value) is Vk. And where C=1, define k=n-1. In the case where the array has a single value, this reduces to k<=C<k+1. In the case of an array with a single index (of 0) - 0 is a valid solution to this constraint. And where C=1, define k=0 ("n-1" is "1-1".)

Webkit treats this case correctly. Sample code for a filter below: which should add a red drop shadow displaced 80 userspace units in x from the filtered content. Firefox displays a black drop shadow (it ignores the feFuncR discrete filter).

<filter id="drop">
  <feComponentTransfer in="SourceAlpha" result="doo">
    <feFuncR type="discrete" tableValues="1" />
  </feComponentTransfer>

  <feOffset dx="80" dy="0"  in="doo" result="shadow"/>
  <feGaussianBlur stdDeviation="20 0" in="shadow" result="blurOut"/>

  <feComponentTransfer in="SourceGraphic" result="unbrightsource">
    <feFuncR type="linear" slope="0.4" />
  </feComponentTransfer>

  <feBlend mode="normal" in="unbrightsource" in2="blurOut" result="final"/>

Comment 1

[Robert Longson [:longsonr]]

Attachment: testcase converted to attachment

Comment 2

[Robert Longson [:longsonr]]

The SVG specification says: The table has n+1 values

You've got 1 value and therefore n = 0.

I can't therefore find a value k such that k/n < C as k/n is infinite unless k = 0. And in that case k + 1 < n is 0 too.

So no solution is possible and a table with 1 value is invalid. The question is what to do about it and I'm thinking we should drop the filter altogether as we would if we had a feColorMatrix type="matrix" having values with other than 20 numbers.

Comment 3

[Robert Longson [:longsonr]]

Forget the previous comment, I'm mixing up discrete and table.

Comment 4

[Robert Longson [:longsonr]]

Attachment: patch

Comment 5

[Robert Longson [:longsonr]]

https://tbpl.mozilla.org/?tree=Try&rev=878cef0d3b17

Comment 6

[Robert Longson [:longsonr]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/7df619463b43

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/7df619463b43