std/png/decode_swizzle_default.wuffs

// Copyright 2020 The Wuffs Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

pri func decoder.filter_and_swizzle!(dst: ptr base.pixel_buffer, workbuf: slice base.u8) base.status,
        choosy,
{
    var dst_pixfmt          : base.pixel_format
    var dst_bits_per_pixel  : base.u32[..= 256]
    var dst_bytes_per_pixel : base.u64[..= 32]
    var dst_bytes_per_row0  : base.u64
    var dst_bytes_per_row1  : base.u64
    var dst_palette         : slice base.u8
    var tab                 : table base.u8

    var y        : base.u32
    var dst      : slice base.u8
    var filter   : base.u8
    var curr_row : slice base.u8
    var prev_row : slice base.u8

    // TODO: the dst_pixfmt variable shouldn't be necessary. We should be able
    // to chain the two calls: "args.dst.pixel_format().bits_per_pixel()".
    dst_pixfmt = args.dst.pixel_format()
    dst_bits_per_pixel = dst_pixfmt.bits_per_pixel()
    if (dst_bits_per_pixel & 7) <> 0 {
        return base."#unsupported option"
    }
    dst_bytes_per_pixel = (dst_bits_per_pixel / 8) as base.u64
    dst_bytes_per_row0 = (this.frame_rect_x0 as base.u64) * dst_bytes_per_pixel
    dst_bytes_per_row1 = (this.frame_rect_x1 as base.u64) * dst_bytes_per_pixel
    dst_palette = args.dst.palette_or_else(fallback: this.dst_palette[..])
    tab = args.dst.plane(p: 0)

    if dst_bytes_per_row1 < tab.width() {
        tab = tab.subtable(
                min_incl_x: 0,
                min_incl_y: 0,
                max_incl_x: dst_bytes_per_row1,
                max_incl_y: tab.height())
    }

    if dst_bytes_per_row0 < tab.width() {
        tab = tab.subtable(
                min_incl_x: dst_bytes_per_row0,
                min_incl_y: 0,
                max_incl_x: tab.width(),
                max_incl_y: tab.height())
    } else {
        tab = tab.subtable(
                min_incl_x: 0,
                min_incl_y: 0,
                max_incl_x: 0,
                max_incl_y: 0)
    }

    y = this.frame_rect_y0
    while y < this.frame_rect_y1 {
        assert y < 0x00FF_FFFF via "a < b: a < c; c <= b"(c: this.frame_rect_y1)
        dst = tab.row_u32(y: y)

        if 1 > args.workbuf.length() {
            return "#internal error: inconsistent workbuf length"
        }
        filter = args.workbuf[0]
        args.workbuf = args.workbuf[1 ..]
        if this.pass_bytes_per_row > args.workbuf.length() {
            return "#internal error: inconsistent workbuf length"
        }
        curr_row = args.workbuf[.. this.pass_bytes_per_row]
        args.workbuf = args.workbuf[this.pass_bytes_per_row ..]

        if filter == 0 {
            // No-op.
        } else if filter == 1 {
            this.filter_1!(curr: curr_row)
        } else if filter == 2 {
            this.filter_2!(curr: curr_row, prev: prev_row)
        } else if filter == 3 {
            this.filter_3!(curr: curr_row, prev: prev_row)
        } else if filter == 4 {
            this.filter_4!(curr: curr_row, prev: prev_row)
        } else {
            return "#bad filter"
        }

        this.swizzler.swizzle_interleaved_from_slice!(
                dst: dst,
                dst_palette: dst_palette,
                src: curr_row)

        prev_row = curr_row
        y += 1
    } endwhile

    return ok
}