The FreeType Project - Bugs: bug #58951, Edge dropout control glitching
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bug #58951: Edge dropout control glitching
Submitter: | - <_194785> | ||
Submitted: | Fri 14 Aug 2020 10:22:45 AM UTC | ||
Severity: | 3 - Normal | Item Group: | Incorrect behaviour |
Status: | None | Privacy: | Public |
Assigned to: | None | Open/Closed: | Open |
Planned Release: | None |
Fri 14 Aug 2020 06:40:06 PM UTC, comment #1: |
- <_194785> |
Fri 14 Aug 2020 10:22:45 AM UTC, original submission:
This is another scenario where FreeType fails to apply the correct TrueType rendering rule.
TrueType rule for vertical dropout control is to render the dropouts from top to bottom. This can be verified by using the Microsoft renderer. Why this matters in rendering is because when dropout control already affected an edge, dropout control an edge a pixel lower will not be activated. FreeType fails this TrueType rule as evidenced by a test of grid of dropout control boxes.
Test string:
In this font, where the higher edges coexist with lower edges in dropout control issue is demonstrated is in the size 16ppem. In this case FreeType does not properly layout the dropout controls.
It is also shown that in some sizes such as 11ppem, the rendering actually depends on the point order. This dependence arises naturally from TrueType rendering implementation. It is shown that FreeType does not have this dependence whatsoever, while TD renderer 2.0 does have a dependence but not quite implemented properly. |
- <_194785> |
Depends on the following items: None found
Items that depend on this one: None found
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Follow 2 latest changes.
Date | Changed by | Updated Field | Previous Value | => | Replaced by |
---|---|---|---|---|---|
2020-08-14 | _194785 | Attached File | - | ![]() |
Added glitcheddropoutedgecontrol.ttf, #49671 |
Attached File | - | ![]() |
Added glitcheddropoutedgecontrol.PNG, #49672 |
original submission:
TD renderer 3.0 is released and the TD renderer 3.0 test rendering for this font is exactly the same as the Microsoft bilevel renderer in the test image.