The cuttlefish tool can be used to convert textures on the command line. This provides the functionality required to create most textures.
When running the cuttlefish tool, one or more input images are provided on the command line. Different arguments are provided for single images, multiple images for an array or 3D texture, or a cube map. The images may optionally be provided from a text file, with one image path per line.
Options are available for common operations on the images. The following operations are provided, and are executed in this order:
- Convert from sRGB to linear. This is performed for formats that cannot natively be sampled as sRGB from the GPU. (note that this may cause a noticeable loss of quality for lower precision formats)
- Resize. Resizing may be an explicit size, next power of 2, or nearest power of 2.
- Rotate.
- Convert to grayscale.
- Convert from a bump map to a normal map.
- Flip along the X axis.
- Flip along the Y axis.
- Swizzle.
- Pre-multiply alpha with color channels.
Even when sRGB sampling is supported by the texture format, resizing, conversion to grayscale, and pre-multiplying alpha is always performed in linear space.
When converting a texture, the format is provided, which is either the color bits for each channel (e.g. R8G8B8A8, R5G6B5, B10G11R11_UFloat) or the name of a compressed format. (e.g. BC3, ETC2_R8G8B8) Some formats allow the type used for the channel to be provided. For example, R16G16B16A16 may be unorm, snorm, uint, int, or float. The final image may be saved as a DDS, KTX, or PVR file.
When running the tool, you may provide the -j parameter to use multiple threaded jobs. The number of jobs may be provided, otherwise it will use all available cores. This is recommended when a single instance of cuttlefish is run, but shouldn't be used if integrated into a build system that will run multiple instances in parallel. (e.g. make with -j provided)
For more detailed information about the command line arguments, run cuttlefish -h.