diff options
Diffstat (limited to 'indra/llimage/llimagej2c.cpp')
| -rw-r--r-- | indra/llimage/llimagej2c.cpp | 34 |
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() |