372782 - add alpha-component rounding to computed style code

Status: RESOLVED FIXED

(Core :: DOM: CSS Object Model, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

To the code from bug 347912 we should add rounding as done in the patch to bug 372770 so that we don't output over-precise alpha components.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Steps to reproduce:
 1. load attachment 257575 [details].
 2. look at the last cell of the last line

Expected results: rgba(128, 17, 41, 0.7)

Actual results: rgba(128, 17, 41, 0.701961)

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: patch

This adds the functions going both directions to nsStyleUtil so that the relationship is clearer to future maintainers.

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Although, it occurs to me that perhaps people will want to do math more often on computed style output, and perhaps we should just leave the computed style code alone, take the rest of the patch, and wontfix this bug.  Thoughts?

Comment 4

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 257588 [details] [diff] [review]
patch

>+nsStyleUtil::ColorComponentToFloat(PRUint8 aAlpha)
>+  if (NSToIntRound(rounded * 255.0f) != aAlpha) {

FloatToColorComponent() here?

I think this is reasonable to do... I doubt people are that much more likely to do math on the computed style, really.

Comment 5

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Checked in to trunk with above change.