LibGfx/BMPWriter: Add support for V3 & V4 DIB headers

This adds very simple support for storing BMP files with
BITMAPV3INFOHEADER and BITMAPV4HEADER. This in turn allows us to
store alpha channels which is nice for our .pp file format. For
the moment no data regarding colorspace is saved, only the bare
minimum to make a valid file.

Some small restructuring of the code is made to hopefully make it
easier to implement more DIB-headers and support for colorspace/gamma
correction in the future.

Author: metmo

Userland/Libraries/LibGfx/BMPWriter.cpp

@@ -10,12 +10,6 @@
 
 namespace Gfx {
 
-constexpr int bytes_per_pixel = 3;
-
-#define FILE_HEADER_SIZE 14
-#define IMAGE_INFORMATION_SIZE 40
-#define PIXEL_DATA_OFFSET FILE_HEADER_SIZE + IMAGE_INFORMATION_SIZE
-
 class OutputStreamer {
 public:
     OutputStreamer(u8* data)
@@ -49,7 +43,7 @@ class OutputStreamer {
     u8* m_data;
 };
 
-static ByteBuffer write_pixel_data(const RefPtr<Bitmap> bitmap, int pixel_row_data_size)
+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);
@@ -62,6 +56,8 @@ static ByteBuffer write_pixel_data(const RefPtr<Bitmap> bitmap, int pixel_row_da
             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();
         }
     }
 
@@ -71,41 +67,74 @@ static ByteBuffer write_pixel_data(const RefPtr<Bitmap> bitmap, int pixel_row_da
 static ByteBuffer compress_pixel_data(const ByteBuffer& pixel_data, BMPWriter::Compression compression)
 {
     switch (compression) {
-    case BMPWriter::Compression::RGB:
+    case BMPWriter::Compression::BI_BITFIELDS:
+    case BMPWriter::Compression::BI_RGB:
         return pixel_data;
     }
 
     VERIFY_NOT_REACHED();
 }
 
-ByteBuffer BMPWriter::dump(const RefPtr<Bitmap> bitmap)
+ByteBuffer BMPWriter::dump(const RefPtr<Bitmap> bitmap, DibHeader dib_header)
 {
-    int pixel_row_data_size = (bytes_per_pixel * 8 * bitmap->width() + 31) / 32 * 4;
+
+    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 buffer = ByteBuffer::create_uninitialized(pixel_data_offset);
 
-    auto pixel_data = write_pixel_data(bitmap, pixel_row_data_size);
+    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);
 
-    int file_size = PIXEL_DATA_OFFSET + pixel_data.size();
+    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(IMAGE_INFORMATION_SIZE); // Header size
-    streamer.write_i32(bitmap->width());        // ImageWidth
-    streamer.write_i32(bitmap->height());       // ImageHeight
-    streamer.write_u16(1);                      // Planes
-    streamer.write_u16(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
+    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
+        }
+    }
 
     buffer.append(pixel_data.data(), pixel_data.size());
     return buffer;

Userland/Libraries/LibGfx/BMPWriter.h

@@ -16,16 +16,25 @@ class BMPWriter {
 public:
     BMPWriter() = default;
 
-    ByteBuffer dump(const RefPtr<Bitmap>);
-
     enum class Compression : u32 {
-        RGB = 0,
+        BI_RGB = 0,
+        BI_BITFIELDS = 3,
+    };
+
+    enum class DibHeader : u32 {
+        Info = 40,
+        V3 = 56,
+        V4 = 108,
     };
 
+    ByteBuffer dump(const RefPtr<Bitmap>, DibHeader dib_header = DibHeader::V4);
+
     inline void set_compression(Compression compression) { m_compression = compression; }
 
 private:
-    Compression m_compression { Compression::RGB };
+    Compression m_compression { Compression::BI_BITFIELDS };
+    int m_bytes_per_pixel { 4 };
+    bool m_include_alpha_channel { true };
 };
 
 }