Add fart.png to write RGBA PNG images

src/fart/main.d

@@ -1,4 +1,7 @@
+import fart.png;
+
 int main(string[] args)
 {
+    png_test();
     return 0;
 }

src/fart/png.d

@@ -0,0 +1,121 @@
+module fart.png;
+
+import std.zlib;
+import std.math;
+import std.digest;
+
+import fart.bfile;
+import fart.crc32;
+import fart.hton;
+
+private immutable ubyte[] HEADER = [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A];
+
+struct IHDR
+{
+    uint width;
+    uint height;
+    ubyte bit_depth;
+    ubyte color_type;
+    ubyte compression;
+    ubyte filter;
+    ubyte interlace;
+    ubyte[0] end;
+
+    this(uint width, uint height)
+    {
+        this.width = htonl(width);
+        this.height = htonl(height);
+        this.bit_depth = 8;
+        this.color_type = 6;
+        this.compression = 0;
+        this.filter = 0;
+        this.interlace = 0;
+    }
+
+    public const(void) * data()
+    {
+        return &this;
+    }
+
+    public size_t data_length()
+    {
+        return end.offsetof;
+    }
+}
+
+struct IDAT
+{
+    private const(ubyte)[] m_data;
+
+    this(ubyte[] data)
+    {
+        m_data = compress(data);
+    }
+
+    public const(void) * data()
+    {
+        return m_data.ptr;
+    }
+
+    public size_t data_length()
+    {
+        return m_data.length;
+    }
+}
+
+struct IEND
+{
+    public const(void) * data()
+    {
+        return &this;
+    }
+
+    public size_t data_length()
+    {
+        return 0;
+    }
+}
+
+private void write_chunk(Chunk)(BFile file, string chunk_type, Chunk chunk)
+{
+    size_t chunk_data_length = chunk.data_length();
+    uint chunk_length_be32 = htonl(cast(uint)chunk_data_length);
+    file.writeObject(chunk_length_be32);
+    file.write(chunk_type);
+    const(ubyte)[] chunk_data = (cast(const(ubyte) *)chunk.data())[0..chunk_data_length];
+    file.write(chunk_data);
+    uint crc_be32 = htonl(crc32(chunk_type, chunk_data));
+    file.writeObject(crc_be32);
+}
+
+public void write_png(string filename, uint width, uint height, ubyte[] data)
+{
+    BFile file = BFile(filename);
+    file.write(HEADER);
+    IHDR ihdr = IHDR(width, height);
+    write_chunk(file, "IHDR", ihdr);
+    IDAT idat = IDAT(data);
+    write_chunk(file, "IDAT", idat);
+    IEND iend;
+    write_chunk(file, "IEND", iend);
+    file.close();
+}
+
+void png_test()
+{
+    ubyte[] pixel_data = [];
+    for (size_t y = 0; y < 500; y++)
+    {
+        /* Filter method 0 (None) */
+        pixel_data ~= [0];
+        for (size_t x = 0; x < 500; x++)
+        {
+            ubyte r = cast(ubyte)(x / 2);
+            ubyte g = 0x80;
+            ubyte b = cast(ubyte)((500 - y) / 2);
+            ubyte a = cast(ubyte)((abs(cast(int)x - 250) + abs(cast(int)y - 250)) / 2);
+            pixel_data ~= [r, g, b, a];
+        }
+    }
+    write_png("out.png", 500, 500, pixel_data);
+}