Vector vs Raster Mode

compose2pdf supports two rendering modes. Choose the right one for your use case.

Vector mode Raster mode
Vector Raster
Download PDF (11 KB) Download PDF (70 KB)

Comparison

Feature VECTOR RASTER
Text selectable Yes No
Scales to any zoom Yes No (bitmap)
File size Smaller (10-100 KB typical) Larger (1-5 MB+)
Rendering path Compose -> Skia -> SVG -> PDFBox Compose -> Skia -> Bitmap -> PDFBox
Font embedding Yes (automatic subsetting) N/A (text is pixels)
Canvas drawing Converted to vector paths Pixel-perfect
Link annotations Yes Yes
Gradients Limited (not preserved in SVG) Full support

Vector mode (default) 

val pdf = renderToPdf(mode = RenderMode.VECTOR) {
    Text("Selectable, scalable text")
}

Best for:

  • Documents with text (reports, invoices, letters)
  • Files that will be printed or zoomed
  • Small file sizes
  • Text search and accessibility

How it works: Compose content is rendered through Skia’s SVGCanvas, producing an SVG string. The SVG is then converted to PDF vector drawing commands via PDFBox. Text remains as positioned glyphs with embedded fonts.

Raster mode 

val pdf = renderToPdf(
    mode = RenderMode.RASTER,
    density = Density(3f),  // Higher density for better quality
) {
    Text("Pixel-perfect rendering")
}

Best for:

  • Gradient-heavy content
  • Complex visual effects not supported in SVG conversion
  • Exact pixel-perfect reproduction needed
  • Content where text selection isn’t important

How it works: Compose content is rendered via ImageComposeScene to a bitmap, then embedded as a lossless PDF image.

Density and quality

The density parameter affects both modes differently:

Density Vector mode Raster mode
Density(1f) Layout at 1:1 pixels Low-res bitmap
Density(2f) (default) Good anti-aliasing Good quality
Density(3f) Slight improvement High quality
Density(4f) Diminishing returns Very high quality, large file

For vector mode, density primarily affects the pixel grid used during Compose layout. Higher density means better sub-pixel positioning and anti-aliasing. The default 2f is a good balance.

For raster mode, density directly controls the resolution of the embedded bitmap. Higher density means more pixels and larger files. Consider 3f for print-quality output.

When to use each 

Is text selection important?
  └── Yes → VECTOR

Does the content use gradients?
  └── Yes → RASTER (or simulate gradients in vector mode)

Is file size a concern?
  └── Yes → VECTOR

Need pixel-perfect reproduction?
  └── Yes → RASTER

Default choice → VECTOR

You can mix modes across pages in a multi-page document by rendering each page separately and merging PDFs. For most documents, VECTOR mode is the right choice.

See also