Bug 120813

I was curious about why blur filters on image backgrounds are incredibly slow. Sampling shows lots of time in GenericTypedArrayView::set(unsigned index, double value) const which is doing a safe double -> int cast with clamping. This comes out of a tight look in the blurring code: for (int x = 0; x < effectWidth; ++x) { int pixelByteOffset = line + x * stride + channel; dstPixelArray->set(pixelByteOffset, static_cast<unsigned char>(sum / dx)); It's crazy that we're wasting time doing double -> int conversion when the caller is passing in an unsigned char. We're converting double -> unsigned char -> double -> int32_t -> uint8_t Bypassing this crap by just filling a uint8_t[] and using dstPixelArray->setRange() makes blurring twice as fast.