Faster text layout

[amolenaar]

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Documentation content changes

What is the current behavior?

Issue Number: N/A

What is the new behavior?

This PR improves the speed of text rendering by about a factor 10. Now Pango layouts are not created all the time, but they are reused. This saves a huge amount of time.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[sourcery-ai]

Sourcery Code Quality Report (beta)

✅ Merging this PR will increase code quality in the affected files by 0.0 out of 10.

	Before	After	Change
Quality	8.69	8.69	0.0
Complexity	1.3	1.33	0.02
Method Length	52.61	52.44	-0.18
Lines	1337	1330	-7

Changed files	Quality Before	Quality After	Quality Change
gaphor/UML/classes/association.py	8.71	8.71	-0.0 ⬇️
gaphor/diagram/shapes.py	8.74	8.73	-0.01 ⬇️
gaphor/diagram/text.py	7.74	8.13	0.39 ⬆️
gaphor/diagram/tests/test_shapes.py	9.16	9.16	0.0
gaphor/diagram/tests/test_text.py	8.75	8.44	-0.31 ⬇️

Here are some functions in these files that still need a tune-up:

File	Function	Quality	Recommendation
gaphor/UML/classes/association.py	AssociationEnd.post_update	3.65	Split out functionality
gaphor/UML/classes/association.py	AssociationItem.post_update	4.72	Split out functionality
gaphor/diagram/text.py	_text_point_at_line_end	4.74	Split out functionality
gaphor/diagram/text.py	_text_point_at_line_center	5.62	Split out functionality
gaphor/diagram/shapes.py	IconBox.child_pos	6.11	Split out functionality

Please see our documentation here for details on how these metrics are calculated.

We are actively working on this report - lots more documentation and extra metrics to come!

Let us know what you think of it via email or our Gitter!

[danyeaw]

Nice cleanup and optimization!