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doc/*.txt: restrict code to 69 columns
some renderers may limit output to 72 and use a 3 space indent; this avoids overflowing into the margin Change-Id: Iaf4e8b71be27ef00fccd1d82b79bf96c01040f10
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James Zern
parent
835392393b
commit
7a0a9935ed
@ -511,8 +511,9 @@ Disposal method (D): 1 bit
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if blend.A = 0 then
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blend.RGB = 0
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else
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blend.RGB = (src.RGB * src.A +
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dst.RGB * dst.A * (1 - src.A / 255)) / blend.A
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blend.RGB =
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(src.RGB * src.A +
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dst.RGB * dst.A * (1 - src.A / 255)) / blend.A
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~~~~~
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* Alpha-blending SHOULD be done in linear color space, by taking into account
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@ -760,33 +761,34 @@ canvas ← new image of size VP8X.canvasWidth x VP8X.canvasHeight with
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loop_count ← ANIM.loopCount
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dispose_method ← ANIM.disposeMethod
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if loop_count == 0:
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loop_count = ∞
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loop_count = ∞
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frame_params ← nil
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assert next chunk in image_data is ANMF
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for loop = 0..loop_count - 1
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clear canvas to ANIM.background_color or application defined color
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until eof or non-ANMF chunk
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frame_params.frameX = Frame X
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frame_params.frameY = Frame Y
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frame_params.frameWidth = Frame Width Minus One + 1
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frame_params.frameHeight = Frame Height Minus One + 1
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frame_params.frameDuration = Frame Duration
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frame_right = frame_params.frameX + frame_params.frameWidth
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frame_bottom = frame_params.frameY + frame_params.frameHeight
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assert VP8X.canvasWidth >= frame_right
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assert VP8X.canvasHeight >= frame_bottom
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for subchunk in 'Frame Data':
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if subchunk.tag == "ALPH":
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assert alpha subchunks not found in 'Frame Data' earlier
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frame_params.alpha = alpha_data
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else if subchunk.tag == "VP8 " OR subchunk.tag == "VP8L":
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assert bitstream subchunks not found in 'Frame Data' earlier
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frame_params.bitstream = bitstream_data
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render frame with frame_params.alpha and frame_params.bitstream on
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canvas with top-left corner at (frame_params.frameX,
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frame_params.frameY), using dispose method dispose_method.
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canvas contains the decoded image.
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Show the contents of the canvas for frame_params.frameDuration * 1ms.
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clear canvas to ANIM.background_color or application defined color
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until eof or non-ANMF chunk
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frame_params.frameX = Frame X
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frame_params.frameY = Frame Y
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frame_params.frameWidth = Frame Width Minus One + 1
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frame_params.frameHeight = Frame Height Minus One + 1
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frame_params.frameDuration = Frame Duration
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frame_right = frame_params.frameX + frame_params.frameWidth
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frame_bottom = frame_params.frameY + frame_params.frameHeight
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assert VP8X.canvasWidth >= frame_right
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assert VP8X.canvasHeight >= frame_bottom
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for subchunk in 'Frame Data':
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if subchunk.tag == "ALPH":
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assert alpha subchunks not found in 'Frame Data' earlier
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frame_params.alpha = alpha_data
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else if subchunk.tag == "VP8 " OR subchunk.tag == "VP8L":
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assert bitstream subchunks not found in 'Frame Data' earlier
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frame_params.bitstream = bitstream_data
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render frame with frame_params.alpha and frame_params.bitstream
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on canvas with top-left corner at (frame_params.frameX,
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frame_params.frameY), using dispose method dispose_method.
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canvas contains the decoded image.
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Show the contents of the canvas for
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frame_params.frameDuration * 1ms.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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@ -480,7 +480,8 @@ void InverseTransform(uint8 red, uint8 green, uint8 blue,
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// color transform deltas
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tmp_red += ColorTransformDelta(trans->green_to_red, green);
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tmp_blue += ColorTransformDelta(trans->green_to_blue, green);
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tmp_blue += ColorTransformDelta(trans->red_to_blue, tmp_red & 0xff);
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tmp_blue +=
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ColorTransformDelta(trans->red_to_blue, tmp_red & 0xff);
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*new_red = tmp_red & 0xff;
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*new_blue = tmp_blue & 0xff;
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@ -920,7 +921,7 @@ int kCodeLengthCodes = 19;
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int kCodeLengthCodeOrder[kCodeLengthCodes] = {
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17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
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};
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int code_length_code_lengths[kCodeLengthCodes] = { 0 }; // All zeros.
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int code_length_code_lengths[kCodeLengthCodes] = { 0 }; // All zeros
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for (i = 0; i < num_code_lengths; ++i) {
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code_length_code_lengths[kCodeLengthCodeOrder[i]] = ReadBits(3);
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}
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@ -1024,7 +1025,8 @@ Given a pixel (x, y) in the ARGB image, we can obtain the corresponding prefix
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codes to be used as follows:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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int position = (y >> prefix_bits) * prefix_xsize + (x >> prefix_bits);
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int position =
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(y >> prefix_bits) * prefix_xsize + (x >> prefix_bits);
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int meta_prefix_code = (entropy_image[pos] >> 8) & 0xffff;
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PrefixCodeGroup prefix_group = prefix_code_groups[meta_prefix_code];
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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@ -1090,8 +1092,8 @@ of pixels (xsize * ysize).
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#### 7.2 Structure of Transforms
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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<optional-transform> ::= (1-bit value 1; <transform> <optional-transform>) |
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1-bit value 0
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<optional-transform> ::=
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(1-bit value 1; <transform> <optional-transform>) | 1-bit value 0
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<transform> ::= <predictor-tx> | <color-tx> | <subtract-green-tx> |
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<color-indexing-tx>
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<predictor-tx> ::= 2-bit value 0; <predictor image>
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@ -1111,32 +1113,33 @@ of pixels (xsize * ysize).
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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<spatially-coded image> ::= <color cache info><meta prefix><data>
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<entropy-coded image> ::= <color cache info><data>
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<color cache info> ::= 1 bit value 0 |
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(1-bit value 1; 4-bit value for color cache size)
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<color cache info> ::=
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1 bit value 0 | (1-bit value 1; 4-bit value for color cache size)
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<meta prefix> ::= 1-bit value 0 |
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(1-bit value 1; <entropy image>)
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<data> ::= <prefix codes><lz77-coded image>
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<entropy image> ::= 3-bit subsample value; <entropy-coded image>
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<prefix codes> ::= <prefix code group> | <prefix code group><prefix codes>
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<prefix codes> ::= <prefix code group> |
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<prefix code group><prefix codes>
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<prefix code group> ::= <prefix code><prefix code><prefix code>
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<prefix code><prefix code>
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See "Interpretation of Meta Prefix Codes" to
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understand what each of these five prefix codes are
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for.
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understand what each of these five prefix
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codes are for.
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<prefix code> ::= <simple prefix code> | <normal prefix code>
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<simple prefix code> ::= see "Simple code length code" for details
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<normal prefix code> ::= <code length code>; encoded code lengths
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<code length code> ::= see section "Normal code length code"
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<lz77-coded image> ::= ((<argb-pixel> | <lz77-copy> | <color-cache-code>)
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<lz77-coded image>) | ""
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<lz77-coded image> ::= ((<argb-pixel> | <lz77-copy> |
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<color-cache-code>) <lz77-coded image>) | ""
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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A possible example sequence:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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<RIFF header><image size>1-bit value 1<subtract-green-tx>
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1-bit value 1<predictor-tx>1-bit value 0<color cache info>1-bit value 0
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<prefix codes><lz77-coded image>
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1-bit value 1<predictor-tx>1-bit value 0<color cache info>
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1-bit value 0<prefix codes><lz77-coded image>
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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[canonical_huff]: https://en.wikipedia.org/wiki/Canonical_Huffman_code
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