using System.IO;
using System.Text;

namespace Flatpack.EditorTools;

/// <summary>
/// Writes greyscale PFM (portable float map) files. The baker stores the 16-bit depth atlas this way: s&amp;box's texture
/// compiler reads PNGs at 8 bits whatever their bit depth, but keeps a float source's precision when it builds an R16
/// texture (measured in iteration 8: every value of a 16-bit ramp came back exact).
/// </summary>
static class FlatpackPfm
{
	/// <summary>
	/// Write <paramref name="pixels"/> (row by row, top row first) as a <paramref name="width"/> x
	/// <paramref name="height"/> single-channel float image.
	/// </summary>
	/// <remarks>
	/// The PFM format stores rows bottom first, but the s&amp;box texture compiler reads the first row as the top, so rows
	/// go out in image order.
	/// </remarks>
	public static void WriteGray( string path, float[] pixels, int width, int height )
	{
		using var file = File.Create( path );
		using var writer = new BinaryWriter( file );

		// "Pf" is one channel; a negative scale means little-endian floats.
		writer.Write( Encoding.ASCII.GetBytes( $"Pf\n{width} {height}\n-1.0\n" ) );
		for ( var i = 0; i < width * height; i++ )
			writer.Write( pixels[i] );
	}
}