gltfpack: Rebalance texture quality table

The main goal of this change is to tweak the UASTC RDO curve. The
initial values here have been picked for early UASTC versions that used
a different RDO algorithm, and haven't been revisited since.

The new table makes it so that at tq 5, we use the same defaults as
basisu (q=128 for ETC1 and l=1 for UASTC RDO), and tweak the table to be
in general a little more aggressive for UASTC. We use different curves
before l=1 and after as the expectation is that for earlier quality
levels, the size is much more important than quality.

The default lambda for tq=8 is a little larger now (0.4 vs 0.3) which
will result in a small size improvement and still good quality by
default. There's maybe a little more room for default lambda to be
higher, but eg lambda=1 does not seem practical for normal maps on a
range of production assets, so we keep the curve for tq=6..10 to be more
quality focused.

The new table is not based on a rigorous fitting of the actual
quality/size curves, but the new tool gltfbasis.py can help find a more
optimal table in the future.

Author: zeux

gltf/basisenc.cpp

@@ -26,15 +26,15 @@ struct BasisSettings
 };
 
 static const BasisSettings kBasisSettings[10] = {
-    {1, 1, 0, 1.5f},
-    {1, 6, 0, 1.f},
-    {1, 20, 1, 1.0f},
-    {1, 50, 1, 0.75f},
-    {1, 90, 1, 0.5f},
-    {1, 128, 1, 0.4f},
-    {1, 160, 1, 0.34f},
-    {1, 192, 1, 0.29f}, // default
-    {1, 224, 2, 0.26f},
+    {1, 1, 0, 4.f},
+    {1, 32, 0, 3.f},
+    {1, 64, 1, 2.f},
+    {1, 96, 1, 1.5f},
+    {1, 128, 1, 1.f}, // quality arguments aligned with basisu defaults
+    {1, 150, 1, 0.8f},
+    {1, 170, 1, 0.6f},
+    {1, 192, 1, 0.4f}, // gltfpack defaults
+    {1, 224, 2, 0.2f},
     {1, 255, 2, 0.f},
 };