Support text runs.

[JimBobSquarePants]

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• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
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• I have provided test coverage for my change (where applicable)

Description

Adds initial support for individual text runs within a text shaping run. Fixes #10

TODO:

• Fix Font size application to individual metrics.
• Capture subscript/superscript/strikethrough metrics for attributes from OS2 table so we can render.
• Capture underline metrics for attributes from Post table so we can render.
• Implement rendering in GlyphMetrics

Example API for setting TextRun properties. Start and End properties are measured in graphemes to avoid slicing up emoji and such like.

var textRuns = new List<TextRun>
{
    new TextRun { Start = 4, End = 9, Font = uiFont.CreateFont(32, FontStyle.Bold), TextAttributes = TextAttribute.Underline | TextAttribute.Strikethrough },
    new TextRun { Start = 26, End = 30, Font = uiFont.CreateFont(32, FontStyle.Italic) }
};

Example Output.

[codecov]

Codecov Report

Merging #251 (7b3ec08) into main (388a24f) will decrease coverage by 0%.
The diff coverage is 84%.

@@         Coverage Diff          @@
##           main   #251    +/-   ##
====================================
- Coverage    83%    83%    -1%     
====================================
  Files       183    186     +3     
  Lines      8985   9430   +445     
  Branches   1425   1478    +53     
====================================
+ Hits       7542   7902   +360     
- Misses     1118   1187    +69     
- Partials    325    341    +16     

Flag	Coverage Δ
unittests	83% <84%> (-1%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/SixLabors.Fonts/FontMetrics.cs	100% <ø> (ø)
src/SixLabors.Fonts/IColorGlyphRenderer.cs	57% <ø> (ø)
...nts/Tables/AdvancedTypographic/GPos/AnchorTable.cs	38% <0%> (ø)
...xLabors.Fonts/Tables/General/Glyphs/GlyphVector.cs	96% <0%> (-4%)	⬇️
src/SixLabors.Fonts/GlyphLayout.cs	76% <56%> (+29%)	⬆️
src/SixLabors.Fonts/GlyphMetrics.cs	61% <60%> (-20%)	⬇️
src/SixLabors.Fonts/GlyphRendererParameters.cs	62% <66%> (+<1%)	⬆️
...Labors.Fonts/Tables/General/Post/PostNameRecord.cs	66% <66%> (ø)
src/SixLabors.Fonts/GlyphShapingData.cs	85% <75%> (+<1%)	⬆️
src/SixLabors.Fonts/Tables/General/PostTable.cs	82% <82%> (ø)
... and 26 more

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[tocsoft]

looking good, couple of comments.

[JimBobSquarePants]

@tocsoft My reasoning re TextOptions was that the new TextRun override in Drawing would be TextDrawingRun

so the following naming looked correct.

• TextOptions - TextRun
• TextDrawingOptions - TextDrawingRun

It also made development a little chicken and eggy since the referenced Drawing version in the Samples project would not build if I change the name.

Changing the name isn't great for upgrades but I'm sure we'll do worse before we ship an RC 😁

[JimBobSquarePants]

Font size now works for each run.

[JimBobSquarePants]

@tocsoft I've captured metrics for subscript, superscript, underline, and strikethrough that can be used for rendering. My assumption would be that this is performed in GlyphMetrics.RenderTo().

I'm gonna need some help with the actual render implementation though, drawing is still not a strong point of mine.

[tocsoft]

@tocsoft I've captured metrics for subscript, superscript, underline, and strikethrough that can be used for rendering. My assumption would be that this is performed in GlyphMetrics.RenderTo().

I'm gonna need some help with the actual render implementation though, drawing is still not a strong point of mine.

Yeah the rendering side I should be able to tackle... ultimately for all this we will need to pass long a TextRun (either synthetic or user created) long to the IGlyphRenderer specifically we should be able to add a new TestRun field to GlyphRendererParameters with the applicable TextRun for the glyph, we can then utilise that on the Drawing side to handle things like changes to the Brush/Pen, and knowing to draw the strike throughs/underlines etc.

GlyphRendererParameters is also where we can access the metrics for underlining etc.

[JimBobSquarePants]

@tocsoft I'm pinches fingers "this close" to cracking superscript and subscript rendering. I've got scaling and positioning working, I just need to fix an indexing issue with the runs (exclusive end turned out to be a bad idea.) so hold out please.

[JimBobSquarePants]

I'll push the updates soon

[tocsoft]

I've split out TextAttributes and TextDecorations into 2 enums as they target different parts of the stack, one effects the layout side and the other is just additional decorations on top.

But we can now override the pen used while drawing decorations.

[JimBobSquarePants]

@tocsoft Just did a BIG update to the layout engine to ensure we generate the correct line-height + offsets for mixed font sizes.

Here's how we compare to Chromium based browsers rendering mixed font sizes. It's now exact.

Six Labors - Left : Chromium - Right

Horizontal

Vertical

Found and fixed a line-break issue in the process and also vertical and horizontal centering was a shade off. Test updates have also been verified visually.

[JimBobSquarePants]

Too tired to fix the .NET 472 rounding silliness just now. Will fix tomorrow.

[JimBobSquarePants]

@tocsoft I'm pretty happy with the shape of this now and with your blessing will get it merged. The last things I wanted to have a look at was font hinting and It looks like I've solved the horizontal alignment problem of the l and i glyphs

Tahoma 11.25pt @ 72 dpi

Unhinted

Hinted

Tahoma 11.25pt @ 96 dpi

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