nsgif__parse_extension_graphic_control()

static nsgif_error fl::third_party::nsgif__parse_extension_graphic_control ( struct nsgif_frame * frame, const fl::u8 * data, fl::size len )

static

Parse the graphic control extension.

Parameters

[in]	frame	The gif frame object we're decoding.
[in]	data	The data to decode.
[in]	len	Byte length of data.

Returns

NSGIF_ERR_END_OF_DATA if more data is needed, NSGIF_OK for success.

Definition at line 756 of file gif.cpp.hpp.

{
    enum {
        GIF_MASK_TRANSPARENCY = 0x01,
        GIF_MASK_DISPOSAL     = 0x1c,
    };
 
    /* 6-byte Graphic Control Extension is:
     *
     *  +0  CHAR    Graphic Control Label
     *  +1  CHAR    Block Size
     *  +2  CHAR    __Packed Fields__
     *              3BITS   Reserved
     *              3BITS   Disposal Method
     *              1BIT    User Input Flag
     *              1BIT    Transparent Color Flag
     *  +3  SHORT   Delay Time
     *  +5  CHAR    Transparent Color Index
     */
    if (len < 6) {
        return NSGIF_ERR_END_OF_DATA;
    }
 
    frame->info.delay = data[3] | (data[4] << 8);
 
    if (data[2] & GIF_MASK_TRANSPARENCY) {
        frame->info.transparency = true;
        frame->transparency_index = data[5];
    }
 
    frame->info.disposal = ((data[2] & GIF_MASK_DISPOSAL) >> 2);
    /* I have encountered documentation and GIFs in the
     * wild that use 0x04 to restore the previous frame,
     * rather than the officially documented 0x03.  I
     * believe some (older?)  software may even actually
     * export this way.  We handle this as a type of
     * "quirks" mode. */
    if (frame->info.disposal == NSGIF_DISPOSAL_RESTORE_QUIRK) {
        frame->info.disposal = NSGIF_DISPOSAL_RESTORE_PREV;
    }
 
    /* if we are clearing the background then we need to
     * redraw enough to cover the previous frame too. */
    frame->redraw_required =
            frame->info.disposal == NSGIF_DISPOSAL_RESTORE_BG ||
            frame->info.disposal == NSGIF_DISPOSAL_RESTORE_PREV;
 
    return NSGIF_OK;
}

References FL_NOEXCEPT, NSGIF_DISPOSAL_RESTORE_BG, NSGIF_DISPOSAL_RESTORE_PREV, NSGIF_DISPOSAL_RESTORE_QUIRK, NSGIF_ERR_END_OF_DATA, and NSGIF_OK.

Referenced by nsgif__parse_frame_extensions().

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