CODEWITHSUNDEEP
ccairo
jforberg
jforberg

Reputation: 6762

Cairo glyph caching

I'm using Cairo for text rendering on an embedded device. I've evaluated the 'toy' text API (i.e. cairo_show_text) and it works very well and is efficient. Unforunately it only supports the most basic operations and always discards the shape immediately.

What I need to do is draw simple text with fill and stroke. When I do this using the slightly more complicated API (cairo_text_path) it works but performance drops to unacceptable levels.

It's a bit difficult to find documentation but I did find this hint:

Be aware cairo_show_text() caches glyphs so is much more efficient if you work with a lot of text.

Where can I read about this glyph caching and how to it also for cairo_text_path? Ideally, is there a code example of this being done? I only need to support this simple use case.

Upvotes: 1

Views: 943

Answers (1)

Youka
Youka

Reputation: 2715

cairo_text_path converts a text with all glyphs to a path and adds him to the context. Rendering this path is expensive because of many segments - dozens of moves, lines, curves for every single glyph.

Glyphs caching by cairo_show_text means that repeating glyphs/characters get rendered once and saved in a much cheaper format (like scanlines, triangles or bitmap) for later occurrences. Because the font doesn't change in-between, this recycling isn't a problem.

You could do this caching by yourself, rendering glyphs on image surfaces and using them as pattern, or simply use bitmap fonts from the beginning.

Upvotes: 2

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