Add `-noNormalDetection` to avoid normal map detection

[illwieckz]

Add -noNormalDetection to avoid normal map detection

Crunch has an algorithm to try to detect normal maps, probably to pick higher quality compressors.

It prevents the compressor to wrongly detect a normal map and select formats like DXT5_AGBR when DXT1 is good enough.

It does not only avoid to produce files in less supported swizzled formats, it also allows to pick smaller formats, sometime saving half of the produced file size.

[illwieckz]

with Metro's rust06e

$ crunch -quality 255 -file /tmp/rust06e.tga -out /tmp/rust06e-dxt5.crn
Apparent type: Normal map, Flags: R G B Non-Flipped 
Input texture: 128x128, Levels: 1, Faces: 1, Format: R8G8B8
Input pixels: 16384, Input file size: 49196, Input bits/pixel: 24.021
Output texture: 128x128, Levels: 8, Faces: 1, Format: DXT5_AGBR
Output pixels: 21845, Output file size: 9364, Output bits/pixel: 3.429

$ crunch -quality 255 -noNormalDetection -file /tmp/rust06e.tga -out /tmp/rust06e-dxt5.crn
Apparent type: 2D map, Flags: R G B Non-Flipped 
Input texture: 128x128, Levels: 1, Faces: 1, Format: R8G8B8
Input pixels: 16384, Input file size: 49196, Input bits/pixel: 24.021
Output texture: 128x128, Levels: 8, Faces: 1, Format: DXT1
Output pixels: 21845, Output file size: 3532, Output bits/pixel: 1.293

With Metro's m77-blanc

$ crunch -quality 255 /tmp/m77-blanc.tga -out /tmp/m77-blanc.crn
Apparent type: Normal map, Flags: R G B Non-Flipped 
Input texture: 32x32, Levels: 1, Faces: 1, Format: R8G8B8
Input pixels: 1024, Input file size: 3116, Input bits/pixel: 24.344
Output texture: 32x32, Levels: 6, Faces: 1, Format: DXT5_AGBR
Output pixels: 1365, Output file size: 771, Output bits/pixel: 4.519

$ crunch -quality 255 -NoNormalDetection /tmp/m77-blanc.tga -out /tmp/m77-blanc.crn
Apparent type: 2D map, Flags: R G B Non-Flipped 
Input texture: 32x32, Levels: 1, Faces: 1, Format: R8G8B8
Input pixels: 1024, Input file size: 3116, Input bits/pixel: 24.344
Output texture: 32x32, Levels: 6, Faces: 1, Format: DXT1
Output pixels: 1365, Output file size: 356, Output bits/pixel: 2.086

Comparison

Image	Format before	Format after	Size before	size after
rust06e	DXT5_AGBR	DXT1	9364	3532
m77-blanc	DXT5_AGBR	DXT1	771	356

[illwieckz]

It looks like crunch only produces DXT5_AGBR files with normal maps, not non-normal maps.

We already use -DXn format for normal maps, so anytime we don't use -DXn we can set -noNormalDetection because we already know the files are not normal maps, and then we never run code that may pick the specific swizzled AGBR format, formats we never need.