Refactor SVG stroke width/bounds calculation

[adroitwhiz]

Resolves

Resolves scratchfoundation/scratch-render#434
Resolves scratchfoundation/scratch-gui#4479

Proposed Changes (EDIT 2020-02-14)

This PR:

1. Changes SvgRenderer._transformMeasurements() to always enlarge the SVG's bounding box by the largest stroke width in the document, even if the unenlarged bounds' width or height are 0.
2. Adds unit tests for SvgRenderer._findLargestStrokeWidth to ensure that it treats stroke attributes the same way as the SVG specification (and ensures that sprites like the one from Doesn't work the block go to position. scratch-gui#4233 don't regress).
3. Fixes SvgRenderer._findLargestStrokeWidth to actually pass those tests.

Reason for Changes

There are certain scenarios (e.g. a perfectly vertical or horizontal line) in which one of the SVG's bounding box dimensions is 0 but the SVG should still have a size.

The previous code (introduced in #73) hid the underlying issue: an empty costume was given incorrect bounds because an empty costume's <g> element had a stroke-width, which was counted as expanding the costume's bounds. This has been properly fixed by changing SvgRenderer._findLargestStrokeWidth to match the SVG spec's definition of strokes.

[adroitwhiz]

After more investigation, it looks like this is basically a revert of #73. This probably breaks other stuff.

[adroitwhiz]

Alright, I changed _findLargestStrokeWidth to not take stroke width into account if stroke="none". This should avoid a regression on scratchfoundation/scratch-gui#4233 while also fixing the two issues mentioned above.

[towerofnix]

@adroitwhiz Okay I was going to suggest a test case be made so that this guaranteedly doesn't break that, but.. I have no idea how you'd make a test case for the VM within the SVG renderer repo. Still, figuring out some automatic way to insure that isn't broken would be good, perhaps?

[adroitwhiz]

This has been refactored to be more thorough/correct, cover more edge cases, and include tests.

I've seen people complain about this very frequently on the Bugs and Glitches forum--will try to find links.

[adroitwhiz]

Related Bugs and Glitches posts:

• Straight lines appear in paint editor but not the stage
• Single-Line Sprite not showing up
• Paint Editor Lines don't show up
• Perfectly Straight Lines won't show up in the stage
• Paint Editor Update: Costume Centering Tool [reply]
• Line Disapearing [sic]
• Sprite lines disseapering [sic]
• Single straight line costumes won't render on the stage.

/cc @fsih

[adroitwhiz]

Before testing to ensure this doesn't regress scratchfoundation/scratch-gui#4233, merge scratchfoundation/scratch-render#561 -- there are some existing rotation-center-related issues in the codebase that may interfere with testing.

[apple502j]

Also fixes:

• Glitch where certain sprite costumes will not appear
• Vertical Lines Not Showing

[adroitwhiz]

This depends on the stroke attribute being moved down to "leaf" items-- blocked on #143

[fsih]

When bug hunting, remember to check for #73 : delete the costume, and then use the pen tool

[fsih]

I think this looks good once we merge STROKABLE_ELEMENTS and GRAPHICAL_ELEMENTS, and I pull it down to test it a bit!

[fsih]

The bug is magically fixed! (by paper.js bump?)