Class: Emfsvg::PngEncoder

Inherits:
Object
  • Object
show all
Defined in:
lib/emfsvg/png_encoder.rb

Overview

Wraps the libpng gem to encode an RGBA pixel buffer as a PNG. Uses the standard libpng write API (png_create_write_struct + png_write_png with PNG_TRANSFORM_IDENTITY) which matches libemf2svg's rgb2png byte-for-byte. The simplified API (Libpng.encode) uses a different filter heuristic that produces different IDAT bytes.

Class Method Summary collapse

Class Method Details

.encode(width, height, rgba_bytes) ⇒ Object 



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# File 'lib/emfsvg/png_encoder.rb', line 14

def encode(width, height, rgba_bytes)
  return "" if width <= 0 || height <= 0
  return "" if rgba_bytes.nil? || rgba_bytes.bytesize < (width * height * 4)

  png = Libpng.encode_standard(width, height, rgba_bytes, pixel_format: "RGBA")
  # Replicate libemf2svg's fmem padding: round up to next multiple
  # of 3 bytes by appending zero bytes. Without this the base64
  # output has `==` padding instead of the trailing `AA`/`A=`/``
  # that libemf2svg produces.
  rem = png.bytesize % 3
  png << ("\x00" * ((3 - rem) % 3)) if rem != 0
  png
end