Class: Pura::Webp::Decoder

Inherits:
Object
  • Object
show all
Defined in:
lib/pura/webp/decoder.rb

Overview

VP8 keyframe (lossy WebP) decoder. This is a Ruby port of golang.org/x/image/vp8, specifically the files decode.go, partition.go, pred.go, predfunc.go, idct.go, token.go, quant.go and reconstruct.go. The port is as line-by-line as practical, including variable names and the ybr workspace layout, so bugs can be cross-checked against the upstream Go source.

Not yet ported: filter.go (loop filter). Pixel-accuracy tests allow tolerance for the small steps this introduces at block edges.

Constant Summary collapse

N_PRED =

—- Predictor mode constants (pred.go) —-

10
PRED_DC = 
0
PRED_TM = 
1
PRED_VE = 
2
PRED_HE = 
3
PRED_RD = 
4
PRED_VR = 
5
PRED_LD = 
6
PRED_VL = 
7
PRED_HD = 
8
PRED_HU = 
9
PRED_DC_TOP = 
10
PRED_DC_LEFT = 
11
PRED_DC_TOPLEFT = 
12
PLANE_Y1_WITH_Y2 =

—- Token plane enumeration (token.go) —-

0
PLANE_Y2 = 
1
PLANE_UV = 
2
PLANE_Y1_SANS_Y2 = 
3
B_COEFF_BASE =

—- ybr workspace offsets (reconstruct.go) —-

256
R_COEFF_BASE = 
256 + 64
WHT_COEFF_BASE = 
256 + 128
YBR_Y_X = 
8
YBR_Y_Y = 
1
YBR_B_X = 
8
YBR_B_Y = 
18
YBR_R_X = 
24
YBR_R_Y = 
18
UNIFORM_PROB = 
128

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data) ⇒ Decoder

Returns a new instance of Decoder.



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# File 'lib/pura/webp/decoder.rb', line 72

def initialize(data)
  @data = data.b
  @pos = 0
end

Class Method Details

.decode(input) ⇒ Object

—- Entry points —-



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# File 'lib/pura/webp/decoder.rb', line 63

def self.decode(input)
  data = if input.is_a?(String) && !input.include?("\0") && input.length < 4096 && File.exist?(input)
           File.binread(input)
         else
           input
         end
  new(data).decode
end

Instance Method Details

#decode ⇒ Object 



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# File 'lib/pura/webp/decoder.rb', line 77

def decode
  parse_riff
end