Add `etcpak` library for faster ETC/ETC2/S3TC imports.

- `etc` module was renamed to `etcpak` and modified to use the new library.
- PKM importer is removed in the process, it's obsolete.
- Old library `etc2comp` is removed.
- S3TC compression no longer done via `squish` (but decompression still is).
- Slight modifications to etcpak sources for MinGW compatibility,
  to fix LLVM `-Wc++11-narrowing` errors, and to allow using vendored or
  system libpng.

Co-authored-by: Rémi Verschelde <rverschelde@gmail.com>

1 files changed, 114 insertions, 0 deletions

diff --git a/thirdparty/etcpak/ColorSpace.cpp b/thirdparty/etcpak/ColorSpace.cpp
new file mode 100644
index 0000000000..0411541066
--- /dev/null
+++ b/thirdparty/etcpak/ColorSpace.cpp
@@ -0,0 +1,114 @@
+#include <math.h>
+#include <stdint.h>
+
+#include "Math.hpp"
+#include "ColorSpace.hpp"
+
+namespace Color
+{
+
+    static const XYZ white( v3b( 255, 255, 255 ) );
+    static const v3f rwhite( 1.f / white.x, 1.f / white.y, 1.f / white.z );
+
+
+    XYZ::XYZ( float _x, float _y, float _z )
+        : x( _x )
+        , y( _y )
+        , z( _z )
+    {
+    }
+
+    XYZ::XYZ( const v3b& rgb )
+    {
+        const float r = rgb.x / 255.f;
+        const float g = rgb.y / 255.f;
+        const float b = rgb.z / 255.f;
+
+        const float rl = sRGB2linear( r );
+        const float gl = sRGB2linear( g );
+        const float bl = sRGB2linear( b );
+
+        x = 0.4124f * rl + 0.3576f * gl + 0.1805f * bl;
+        y = 0.2126f * rl + 0.7152f * gl + 0.0722f * bl;
+        z = 0.0193f * rl + 0.1192f * gl + 0.9505f * bl;
+    }
+
+    static float revlab( float t )
+    {
+        const float p1 = 6.f/29.f;
+        const float p2 = 4.f/29.f;
+
+        if( t > p1 )
+        {
+            return t*t*t;
+        }
+        else
+        {
+            return 3 * sq( p1 ) * ( t - p2 );
+        }
+    }
+
+    XYZ::XYZ( const Lab& lab )
+    {
+        y = white.y * revlab( 1.f/116.f * ( lab.L + 16 ) );
+        x = white.x * revlab( 1.f/116.f * ( lab.L + 16 ) + 1.f/500.f * lab.a );
+        z = white.z * revlab( 1.f/116.f * ( lab.L + 16 ) - 1.f/200.f * lab.b );
+    }
+
+    v3i XYZ::RGB() const
+    {
+        const float rl =  3.2406f * x - 1.5372f * y - 0.4986f * z;
+        const float gl = -0.9689f * x + 1.8758f * y + 0.0415f * z;
+        const float bl =  0.0557f * x - 0.2040f * y + 1.0570f * z;
+
+        const float r = linear2sRGB( rl );
+        const float g = linear2sRGB( gl );
+        const float b = linear2sRGB( bl );
+
+        return v3i( clampu8( int32_t( r * 255 ) ), clampu8( int32_t( g * 255 ) ), clampu8( int32_t( b * 255 ) ) );
+    }
+
+
+    Lab::Lab()
+        : L( 0 )
+        , a( 0 )
+        , b( 0 )
+    {
+    }
+
+    Lab::Lab( float L, float a, float b )
+        : L( L )
+        , a( a )
+        , b( b )
+    {
+    }
+
+    static float labfunc( float t )
+    {
+        const float p1 = (6.f/29.f)*(6.f/29.f)*(6.f/29.f);
+        const float p2 = (1.f/3.f)*(29.f/6.f)*(29.f/6.f);
+        const float p3 = (4.f/29.f);
+
+        if( t > p1 )
+        {
+            return pow( t, 1.f/3.f );
+        }
+        else
+        {
+            return p2 * t + p3;
+        }
+    }
+
+    Lab::Lab( const XYZ& xyz )
+    {
+        L = 116 * labfunc( xyz.y * rwhite.y ) - 16;
+        a = 500 * ( labfunc( xyz.x * rwhite.x ) - labfunc( xyz.y * rwhite.y ) );
+        b = 200 * ( labfunc( xyz.y * rwhite.y ) - labfunc( xyz.z * rwhite.z ) );
+    }
+
+    Lab::Lab( const v3b& rgb )
+    {
+        new(this) Lab( XYZ( rgb ) );
+    }
+
+}