GlyphAtlas

Remarks

Dynamic rather than built ahead. CJK alone is tens of thousands of glyphs and a font may carry more; an atlas holding every glyph a font can draw is a texture nobody has the memory for, and one holding the glyphs an interface actually uses is a few hundred.

Shelf packing. Rows are opened as needed, each as tall as the first glyph that starts it, and glyphs fill along the row. It wastes the difference between a row's height and each glyph's — real, and bounded by how much glyph heights vary within one field resolution, which is not much. A skyline packer would waste less and would have to move entries to stay that way, and moving one entry invalidates a texture coordinate somebody is holding.

⚠ An evicted slot is reused only by a glyph that fits it. Eviction leaves a hole of one exact size, and a hole is worth having only if the next glyph is no larger — so the freed slots are kept per shelf and matched by width. What that cannot do is answer a glyph wider than every hole while the atlas is nominally full, which is what Compact is for: it rebuilds the packing from the live entries and changes every region, so Version moves and a caller holding coordinates has to ask again.

Fields and properties (10)

• public int Width

  The texture's width.

• public int Height

  The texture's height.

• public float[] Pixels

  The three channels per pixel, row-major. What a renderer uploads.

• public int Count

  How many glyphs are held.

• public long Hits

  How many lookups were answered from the atlas.

• public long Misses

  How many lookups had nothing to answer with.

• public long Evictions

  How many entries have been evicted to make room.

• public int Version

  Moves whenever every region changes, which only Compact does.

• public int Revision

  Moves whenever the pixels change: a glyph added, or the whole thing repacked.

• public bool Dirty

  Whether the texture's contents have changed since the flag was last cleared.

Methods (6)

• public GlyphAtlas(int width = 1024, int height = 1024, int padding = 1)

  Creates an atlas.

• public void Uploaded()

  Clears Dirty, after a renderer has uploaded the texture.

• public bool TryGet(GlyphKey key, out AtlasRegion region)

  Finds a glyph's field, marking it as the most recently used.

• public bool Add(GlyphKey key, DistanceFieldBitmap field, out AtlasRegion region)

  Puts a glyph's field into the atlas, making room if it has to.

• public void Clear()

  Throws everything away.

• public void Compact()

  Rebuilds the packing from the live entries, tightest first.

Used by (18)

• UiHostHelloUi
• GlyphAtlasTestsVixen.Ui.Text.Tests
• GlyphFieldCacheVixen.Ui.Text
• GlyphFieldCacheTestsVixen.Ui.Text.Tests
• IconAtlasVixen.Ui
• IconAtlasTestsVixen.Ui.Tests
• NineSliceImageTestsVixen.Ui.Tests
• PathTessellationCacheTestsVixen.Ui.Tests
• SoftwareUiRasterizerVixen.Ui.Testing
• UiFrameLifetimeTestsVixen.Graphics.Golden.Tests
• UiGeometryBuilderVixen.Ui
• UiGeometryTestsVixen.Ui.Tests
• UiImageTestsVixen.Graphics.Golden.Tests
• UiInterfaceVixen.Ui.Renderer
• UiRendererVixen.Ui.Renderer
• UiTestVixen.Ui.Testing
• VideoInUiTestsVixen.Video.Rendering.Tests
• EditorHostVixen.Editor.Host