Authors' implementation of my SIGGRAPH Asia 2019 Technical Briefs (The Power of Box Filters: Real-time Approximation to Large Convolution Kernel by Box-filtered Image Pyramid) demo I (just for reference). A very fast approximation to large-kernel Gaussian blur with nonuniform blur radii, by making use of box-filtered mip maps V-cycle (theoratically related to Haar wavelet tranforms). The mathematical model can be found in the PDF file.