DDSTool manual

Version History Version 3/11/08 	Initial Version

System Requirements and Installation
DDSTool runs on any Macintosh or Windows machine that runs X-Plane. It is a single executable that can be decompressed into any directory; for compatibility with X-Grinder it must be in the same directory as X-Grinder. See the X-Grinder manual for more details.

Using DDSTool
DDSTool converts PNG files to DDS files for use with X-Plane. DDSTool always takes a PNG file and creates a DDS file of the same name but with the .dds suffix.

To convert a PNG file using XGrinder and DDSTool, simply drag the PNG file into the X-Grinder window.

Using DDSTool in the Command-Line
The command-line syntax for DDSTool is:

DDSTool

DDSTool provides five modes of conversion. These options list both the menu choice in XGrinder and the command-line option. See the next section for details on DXT1 vs. DXT3 vs. DXT5.

Mode 1: Auto-pick compression
--png2dxt

In this mode DDSTool will use DXT1 compression for PNG files with no alpha channel and DXT5 for PNG files with an alpha channel.

Mode 2: Use DXT1 Compression (1-bit alpha)
--png2dxt1

In this mode, the PNG file is always compressed using DXT1.

Mode 3: Use DXT3 Compression (high-freq alpha)
--png2dxt3

In this mode, the PNG file is always compressed using DXT3.

Mode 4: Use DXT5 Compression (smooth alpha)
--png2dxt5

In this mode, the PNG file is always compressed using DXT5.

Mode 5: Use no compression (requires mipmap)
--png2rgb

This mode builds an uncompressed RGB DDS file. The image file must contain the entire mipmap tree (justified to the bottom of the PNG file with each mip to the right of the previous one).

This mode is NOT recommended for scenery use; there are only a few very special cases where X-Plane will allow an uncompressed DDS file, and generally they do not occur in either third party airplanes or third party scenery!

Forms of DXT Compression
DXT1, DXT3, and DXT5 are the compression schemes that DDSTool can write into a DDS image file; they differ in how the alpha channel (transparency) of the image is handled:


 * DXT1 contains "1-bit" alpha - that is, the alpha is either 100% opaque or totally transparent. The 1-bit alpha is part of the color information of the image; there is no RGB color data behind the transparent parts.  This can lead to artifacts around the edges of the image file.  DXT1 files use half the VRAM of DXT3/DXT5, offering an 8:1 compression ratio over RGB+alpha vs. a 4:1 compression ratio for DXT3/DXT5.


 * Use DXT1 when your image contains no alpha information, or when the alpha is just a sharp mask and a no-blend attribute prevents "color bleed" near the edges of the image.


 * Note: X-Plane will treat DXT1 as having alpha if there is at least one transparent pixel; it will treat the image as not having an alpha channel if there are no transparent pixels. This means that you can use DXT1 for night lighting masks as long as you don't have translucency (variable alpha) in your night lighting texture.


 * DXT3 contains 4-bit uncompressed alpha; smooth transitions of alpha will look like they have distinct "steps", but very high frequency alpha transitions can always be preserved. Use DXT3 compression only if your image has a complex alpha channel with rapid changes, and DXT5 produces noticeable artifacts.


 * DXT5 contains a compressed alpha channel; the compression can capture gentle washes of alpha reasonably well, and can also capture high frequency data. DXT5 is usually the best choice for any image with translucency; if your image has alpha, try DXT5 first.

The technical details of the DXTn compression schemes can be found here.