gid-decoding_png.ads

private package GID.Decoding_PNG is

  type PNG_Chunk_Tag is
    --
    --  Critical chunks
    --
   (IHDR,  --    must be the first chunk; it contains the header.
    PLTE,  --    contains the palette; list of colors.
    IDAT,  --    contains the image, which may be split among multiple IDAT chunks.
    IEND,  --    marks the image end.
    --
    --  Ancillary chunks
    --
    bKGD,  --    gives the default background color.
    cHRM,  --    gives the chromaticity coordinates of the display primaries and white point.
    gAMA,  --    specifies gamma.
    hIST,  --    can store the histogram, or total amount of each color in the image.
    iCCP,  --    is an ICC color profile.
    iTXt,  --    contains UTF-8 text, compressed or not, with an optional language tag.
    pHYs,  --    holds the intended pixel size and/or aspect ratio of the image.
    sBIT,  --    (significant bits) indicates the color-accuracy of the source data.
    sPLT,  --    suggests a palette to use if the full range of colors is unavailable.
    sRGB,  --    indicates that the standard sRGB color space is used.
    tEXt,  --    can store text that can be represented in ISO/IEC 8859-1.
    tIME,  --    stores the time that the image was last changed.
    tRNS,  --    contains transparency information.
    zTXt,  --    contains compressed text with the same limits as tEXt.
    --
    --  Public extentions
    --  PNG Extensions and Register of Public Chunks and Keywords
    --
    oFFs,  --  image offset from frame or page origin
    pCAL,  --  physical calibration of pixel values
    sCAL,  --  physical scale of image subject
    sTER,  --  stereographic subimage layout
    gIFg,  --  GIF Graphic Control Extension
    gIFx,  --  GIF Application Extension
    fRAc,  --  fractal image parameters
    --
    --  Private chunks (not defined in the ISO standard)
    --
    vpAg,   --  Used in ImageMagick to store "virtual page" size
    spAL,
    prVW,
    cmOD,
    cmPP,
    cpIp,
    mkBF,
    mkBS,
    mkBT,
    mkTS,
    pcLb,
    iDOT,   --  Apple proprietary chunk
    --
    --  Animated PNG (APNG - https://en.wikipedia.org/wiki/APNG )
    --
    acTL,   --  Animation control chunk
    fcTL,   --  Frame control chunk
    fdAT,   --  Frame data chunk
    --
    unknown_ancillary_chunk);

  type Chunk_Header is record
    length : U32;
    kind   : PNG_Chunk_Tag;
  end record;

  procedure Read_Chunk_Header
    (image : in out Image_Descriptor; ch : out Chunk_Header);

  --------------------
  -- Image decoding --
  --------------------

  generic
    type Primary_Color_Range is mod <>;
    with procedure Set_X_Y (x, y : Natural);
    with procedure Put_Pixel
      (red, green, blue : Primary_Color_Range;
       alpha            : Primary_Color_Range);
    with procedure Feedback (percents : Natural);
    --  mode : Display_Mode;
    --         --  mode = redundant -> interlaced PNG
               --    is displayed during decoding.
  --
  procedure Load
    (image      : in out Image_Descriptor;
     next_frame :    out Ada.Calendar.Day_Duration);

end GID.Decoding_PNG;