API Reference: TextBlob & Builder

A TextBlob is an immutable, optimized representation of a set of glyphs. It is the fastest way to draw text in Skija if the text layout (position of glyphs) does not change.

TextBlob

TextBlob combines glyphs, positions, and fonts into a single object that can be reused.

Properties

• getBounds(): Returns the conservative bounding box of the blob.
• getUniqueId(): Returns a unique identifier for caching.
• serializeToData(): Serializes the blob to a Data object.

Creation from Positions

If you have already calculated glyph positions (e.g., using Shaper or manually), you can create a blob directly.

// Horizontal positions only (y is constant)
TextBlob blob = TextBlob.makeFromPosH(glyphs, xPositions, y, font);

// Full (x, y) positions for each glyph
TextBlob blob2 = TextBlob.makeFromPos(glyphs, points, font);

// RSXform (Rotation + Scale + Translate) for each glyph
TextBlob blob3 = TextBlob.makeFromRSXform(glyphs, xforms, font);

Drawing

canvas.drawTextBlob(blob, x, y, paint);

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TextBlobBuilder

TextBlobBuilder allows you to construct a TextBlob by appending multiple "runs" of text. A "run" is a sequence of glyphs that share the same Font and Paint.

Basic Usage

TextBlobBuilder builder = new TextBlobBuilder();

// Append a run of text
builder.appendRun(font, "Hello ", 0, 0);

// Append another run (e.g., different style or position)
builder.appendRun(boldFont, "World!", 100, 0);

// Build the immutable TextBlob
TextBlob blob = builder.build();

Advanced Appending

• appendRun(font, glyphs, x, y, bounds): Appends glyphs with a shared origin.
• appendRunPosH(...): Appends glyphs with explicit X positions.
• appendRunPos(...): Appends glyphs with explicit (X, Y) positions.
• appendRunRSXform(...): Appends glyphs with full affine transformations (rotation/scale).

Performance Tip

If you are drawing the same paragraph of text multiple times (even if the canvas moves), create a TextBlob once and reuse it. This avoids re-calculating glyph positions and shapes.