BMPWriter.cpp

/*
 * Copyright (c) 2020, Ben Jilks <benjyjilks@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibGfx/BMPWriter.h>
#include <LibGfx/Bitmap.h>

namespace Gfx {

class OutputStreamer {
public:
    OutputStreamer(u8* data)
        : m_data(data)
    {
    }

    void write_u8(u8 i)
    {
        *(m_data++) = i;
    }

    void write_u16(u16 i)
    {
        *(m_data++) = i & 0xFF;
        *(m_data++) = (i >> 8) & 0xFF;
    }

    void write_u32(u32 i)
    {
        write_u16(i & 0xFFFF);
        write_u16((i >> 16) & 0xFFFF);
    }

    void write_i32(i32 i)
    {
        write_u32(static_cast<u32>(i));
    }

private:
    u8* m_data;
};

static ByteBuffer write_pixel_data(const RefPtr<Bitmap> bitmap, int pixel_row_data_size, int bytes_per_pixel, bool include_alpha_channel)
{
    int image_size = pixel_row_data_size * bitmap->height();
    auto buffer = ByteBuffer::create_uninitialized(image_size);

    int current_row = 0;
    for (int y = bitmap->physical_height() - 1; y >= 0; --y) {
        auto* row = buffer.data() + (pixel_row_data_size * current_row++);
        for (int x = 0; x < bitmap->physical_width(); x++) {
            auto pixel = bitmap->get_pixel(x, y);
            row[x * bytes_per_pixel + 0] = pixel.blue();
            row[x * bytes_per_pixel + 1] = pixel.green();
            row[x * bytes_per_pixel + 2] = pixel.red();
            if (include_alpha_channel)
                row[x * bytes_per_pixel + 3] = pixel.alpha();
        }
    }

    return buffer;
}

static ByteBuffer compress_pixel_data(const ByteBuffer& pixel_data, BMPWriter::Compression compression)
{
    switch (compression) {
    case BMPWriter::Compression::BI_BITFIELDS:
    case BMPWriter::Compression::BI_RGB:
        return pixel_data;
    }

    VERIFY_NOT_REACHED();
}

ByteBuffer BMPWriter::dump(const RefPtr<Bitmap> bitmap, DibHeader dib_header)
{

    switch (dib_header) {
    case DibHeader::Info:
        m_compression = Compression::BI_RGB;
        m_bytes_per_pixel = 3;
        m_include_alpha_channel = false;
        break;
    case DibHeader::V3:
    case DibHeader::V4:
        m_compression = Compression::BI_BITFIELDS;
        m_bytes_per_pixel = 4;
        m_include_alpha_channel = true;
    }

    const size_t file_header_size = 14;
    size_t pixel_data_offset = file_header_size + (u32)dib_header;

    int pixel_row_data_size = (m_bytes_per_pixel * 8 * bitmap->width() + 31) / 32 * 4;
    int image_size = pixel_row_data_size * bitmap->height();
    auto buffer = ByteBuffer::create_uninitialized(pixel_data_offset);

    auto pixel_data = write_pixel_data(bitmap, pixel_row_data_size, m_bytes_per_pixel, m_include_alpha_channel);
    pixel_data = compress_pixel_data(pixel_data, m_compression);

    size_t file_size = pixel_data_offset + pixel_data.size();
    OutputStreamer streamer(buffer.data());
    streamer.write_u8('B');
    streamer.write_u8('M');
    streamer.write_u32(file_size);
    streamer.write_u32(0);
    streamer.write_u32(pixel_data_offset);

    streamer.write_u32((u32)dib_header);       // Header size
    streamer.write_i32(bitmap->width());       // ImageWidth
    streamer.write_i32(bitmap->height());      // ImageHeight
    streamer.write_u16(1);                     // Planes
    streamer.write_u16(m_bytes_per_pixel * 8); // BitsPerPixel
    streamer.write_u32((u32)m_compression);    // Compression
    streamer.write_u32(image_size);            // ImageSize
    streamer.write_i32(0);                     // XpixelsPerMeter
    streamer.write_i32(0);                     // YpixelsPerMeter
    streamer.write_u32(0);                     // TotalColors
    streamer.write_u32(0);                     // ImportantColors

    if (dib_header == DibHeader::V3 || dib_header == DibHeader::V4) {
        streamer.write_u32(0x00ff0000); // Red bitmask
        streamer.write_u32(0x0000ff00); // Green bitmask
        streamer.write_u32(0x000000ff); // Blue bitmask
        streamer.write_u32(0xff000000); // Alpha bitmask
    }

    if (dib_header == DibHeader::V4) {
        streamer.write_u32(0); // Colorspace

        for (int i = 0; i < 12; i++) {
            streamer.write_u32(0); // Endpoints
        }
    }

    if (!buffer.try_append(pixel_data.data(), pixel_data.size()))
        dbgln("Failed to write {} bytes of pixel data to buffer", pixel_data.size());
    return buffer;
}

}