Bug 151116 – Web Inspector: Code coverage profiler: incorrect "in-viewport" detection algorithm

• Component: Web Inspector
• Status: RESOLVED FIXED

[Nikita Vasilyev]

The following "is block in the viewport" code is incorrect:

    basicBlocks = basicBlocks.filter(function(block) {
        return (block.startOffset >= startOffset && block.startOffset <= endOffset) || 
               (block.startOffset <= startOffset && block.endOffset >= endOffset);
    });

https://github.com/WebKit/webkit/blob/f70c51a855acc626ec921f7400a69ede4bffac96/Source/WebInspectorUI/UserInterface/Controllers/BasicBlockAnnotator.js#L68-L71

Let's break it down into smaller pieces:

    block.startOffset >= startOffset && block.startOffset <= endOffset

returns true for the following cases (tilt your head 90 degrees):

Viewport: [---]
Block:      [---]


    block.startOffset <= startOffset && block.endOffset >= endOffset

returns true for the following case:

Viewport:  [---]
Block:   [------]


The following case isn't covered, e.g. the filter function wrongly returns false:

Viewport:  [---]
Block:   [---]

[Radar WebKit Bug Importer]

<rdar://problem/23485933>

[Nikita Vasilyev]

Let's outline all the possible scenarios.

Intersect:
A: [---]
B:   [---]

A: [-----]
B:   [-]

A:   [-]
B: [-----]

A:   [---]
B: [---]


Don't intersect:
A: [---]
B:       [---]

A:       [---]
B: [---]


The easiest way to check if two ranges intersect is to check if they don't intersect. It is also the fastest way.

[Nikita Vasilyev]

Created attachment 265220 [details]
Patch

[Blaze Burg]

Comment on attachment 265220 [details]
Patch

r=me

[WebKit Commit Bot]

Comment on attachment 265220 [details]
Patch

Clearing flags on attachment: 265220

Committed r192264: <http://trac.webkit.org/changeset/192264>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.