bugThe FreeType Project - Bugs: bug #58951, Edge dropout control glitching

 
 

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bug #58951: Edge dropout control glitching

Submitted by:  - <_194785>
Submitted on:  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: 

original submission:

> 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.


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.

- <_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>

 

Attached Files
file #49671:  glitcheddropoutedgecontrol.ttf added by _194785 (6KiB - application/octet-stream)

 

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

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