Merge pull request #6029 from secondlife/geenz/26.3-texture-streaming-revert

Remove texture streaming changes from 26.3

1 files changed, 29 insertions, 5 deletions

diff --git a/indra/llimage/llimagej2c.cpp b/indra/llimage/llimagej2c.cpp
index 8099a18045..5a941dc958 100644
--- a/indra/llimage/llimagej2c.cpp
+++ b/indra/llimage/llimagej2c.cpp
@@ -268,11 +268,35 @@ S32 LLImageJ2C::calcHeaderSizeJ2C()
 //static
 S32 LLImageJ2C::calcDataSizeJ2C(S32 w, S32 h, S32 comp, S32 discard_level, F32 rate)
 {
-    // Dispatch to the linked impl so OpenJPEG (block-aligned, needs
-    // over-allocation) and KDU (packet-aligned, lean) each return what
-    // their decoder actually needs.
-    static std::unique_ptr<LLImageJ2CImpl> s_estimator(fallbackCreateLLImageJ2CImpl());
-    return s_estimator->estimateDataSize(w, h, comp, discard_level, rate);
+    // Note: This provides an estimation for the first to last quality layer of a given discard level
+    // This is however an efficient approximation, as the true discard level boundary would be
+    // in general too big for fast fetching.
+    // For details about the equation used here, see https://wiki.lindenlab.com/wiki/THX1138_KDU_Improvements#Byte_Range_Study
+
+    // Estimate the number of layers. This is consistent with what's done for j2c encoding in LLImageJ2CKDU::encodeImpl().
+    constexpr S32 precision = 8; // assumed bitrate per component channel, might change in future for HDR support
+    constexpr S32 max_components = 4; // assumed the file has four components; three color and alpha
+    // Use MAX_IMAGE_SIZE_DEFAULT (currently 2048) if either dimension is unknown (zero)
+    S32 width  = (w > 0) ? w : 2048;
+    S32 height = (h > 0) ? h : 2048;
+    S32 max_dimension = llmax(width, height); // Find largest dimension
+    S32 block_area = MAX_BLOCK_SIZE * MAX_BLOCK_SIZE; // Calculated initial block area from established max block size (currently 64)
+    S32 max_layers = (S32)llmax(llround(log2f((float)max_dimension) - log2f((float)MAX_BLOCK_SIZE)), 4); // Find number of powers of two between extents and block size to a minimum of 4
+    block_area *= llmax(max_layers, 1); // Adjust initial block area by max number of layers
+    S32 totalbytes = (S32) (MIN_LAYER_SIZE * max_components * precision); // Start estimation with a minimum reasonable size
+    S32 block_layers = 0;
+    while (block_layers <= max_layers) // Walk the layers
+    {
+        if (block_layers <= (5 - discard_level))  // Walk backwards from discard 5 to required discard layer.
+            totalbytes += (S32) (block_area * max_components * precision * rate); // Add each block layer reduced by assumed compression rate
+        block_layers++; // Move to next layer
+        block_area *= 4; // Increase block area by power of four
+    }
+
+    totalbytes /= 8; // to bytes
+    totalbytes += calcHeaderSizeJ2C();  // header
+
+    return totalbytes;
 }
 
 S32 LLImageJ2C::calcHeaderSize()