[TxMt] Re: Large file does not properly paint text when scrolling in v2.0 on MacOS Catalina

[Allan Odgaard]

On 11 Oct 2019, at 9:02, Jacob Carlborg wrote:

> TextMate has always had problems with large files since the move to 
> TextMate 2. I think the text rendering is implemented differently 
> compared to TextMate 1.5.

TextMate 2 got a completely new layout engine that supported 
proportional width fonts, indented soft wrap, mixed fonts with different 
line heights, folding arbitrary subsets, enabling/disabling soft wrap 
for subsets, etc.

As obtaining text metrics is a slow operation, I decided to make it 
lazy, which is what has resulted in the unsatisfying behavior with soft 
wrap:

When scrolling through a file, lines will wrap the first time they are 
rendered, causing the total height of the document to change, and this 
can cause text to “jump around”.

This is worst if opening a file with many long soft wrapped lines, and 
then moving to the bottom, because the bottom of the file will then 
change after having moved there, and scrolling up is also very confusing 
when hitting a line that hasn’t been wrapped yet.

I’ve decided that rather than try to fix this for TextMate 2.0 it is 
better to write a new layout engine because the soft wrap issue is not 
the only thing I want to address.

I don’t want to say anything that can be interpreted as promises or 
pre-announcements, but the new layout engine / text view is what I am 
currently working on, and in addition to fixing the lazy layout issue, 
performance for large files (as in hundreds of megabytes) is also a high 
priority.
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