Rasterizes a font into an SDF atlas texture (r8unorm) + FontMetrics. Browser-only (Canvas
2D). One glyph at a time: draw padded, read its alpha, distance-transform it, shelf-pack the SDF
into one big Uint8Array, then upload. Metrics place each glyph quad relative to the pen baseline.
Rasterizes a font into an SDF atlas texture (r8unorm) + FontMetrics. Browser-only (Canvas 2D). One glyph at a time: draw padded, read its alpha, distance-transform it, shelf-pack the SDF into one big
Uint8Array, then upload. Metrics place each glyph quad relative to the pen baseline.