1 files changed, 30 insertions, 0 deletions
diff --git a/indra/llkdu/llimagej2ckdu.cpp b/indra/llkdu/llimagej2ckdu.cpp
index e7ac6bdb31..4330b1e5b1 100644
--- a/indra/llkdu/llimagej2ckdu.cpp
+++ b/indra/llkdu/llimagej2ckdu.cpp
@@ -1513,3 +1513,33 @@ void kdc_flow_control::process_components()
         }
     }
 }
+
+// Layer-factored byte estimator. Walks the resolution pyramid to count
+// layers, weights by layer_factor, then picks between a sqrt-based "new"
+// estimate and a raw-dimensions "old" estimate per TextureNewByteRange.
+// Reference: https://wiki.lindenlab.com/wiki/THX1138_KDU_Improvements#Byte_Range_Study
+S32 LLImageJ2CKDU::estimateDataSize(S32 w, S32 h, S32 comp, S32 discard_level, F32 rate) const
+{
+    S32 width  = (w > 0) ? w : 2048;
+    S32 height = (h > 0) ? h : 2048;
+    S32 nb_layers = 1;
+    S32 surface = width * height;
+    S32 s = MAX_BLOCK_SIZE * MAX_BLOCK_SIZE;
+    while (surface > s)
+    {
+        nb_layers++;
+        s *= 4;
+    }
+    F32 layer_factor = 3.0f * (7 - llclamp(nb_layers, 1, 6));
+
+    width  >>= discard_level;
+    height >>= discard_level;
+    width  = llmax(width, 1);
+    height = llmax(height, 1);
+
+    S32 new_bytes = (S32)(sqrtf((F32)(width * height)) * (F32)comp * rate * 1000.f / layer_factor);
+    S32 old_bytes = (S32)((F32)(width * height * comp) * rate);
+    S32 bytes = (LLImage::useNewByteRange() && (new_bytes < old_bytes)) ? new_bytes : old_bytes;
+    bytes = llmax(bytes, LLImageJ2C::calcHeaderSizeJ2C());
+    return bytes;
+}