MaskedOcclusionCulling | Example code for the research paper

The code is optimized for runtime performance and may require a long time to compile due to heavy code inlining. This can be worked around by compiling a library file. An alternative solution is to disable whole program optimizations for the MaskedOcclusionCulling.cpp, MaskedOcclusionCullingAVX2.cpp and MaskedOcclusionCullingAVX512.cpp files. It does not impact runtime performance, but greatly reduces the time of program linking. Most inputs are given as clip space (x,y,w) coordinates assuming the same right handed coordinate system as used by DirectX and OpenGL (x positive right, y positive up and w positive in the view direction). Note that we use the clip space w coordinate for depth and disregard the z coordinate. Internally our masked hierarchical depth buffer stores depth = 1 / w. The TestRect() function is an exception and instead accepts normalized device coordinates (NDC), (x' = x/w, y' = y/w), where the visible screen region maps to the range [-1,1] for x' and y' (x positive right and y positive up). Again, this is consistent with both DirectX and OpenGL behavior. By default, the screen space coordinate system used internally to access our hierarchical depth buffer follows DirectX conventions (y positive down), which is not consistent with OpenGL (y positive up). This can be configured by changing the USE_D3D define. The screen space coordinate system affects the layout of the buffer returned by the ComputePixelDepthBuffer() function, scissor rectangles (which are specified in screen space coordinates), and rasterization tie-breaker rules if PRECISE_COVERAGE is enabled.
We begin by creating a new instance of the occlusion culling object. The object is created using the static Create() function rather than a standard constructor, and can be destroyed using the Destroy() function. The reason for using the factory Create()/Destroy() design pattern is that we want to support custom (aligned) memory allocators, and that the library choses either the AVX-512, AVX or SSE implementation based on the CPU's capabilities. The created object is empty and has no hierarchical depth buffer attached, so we must first allocate a buffer using the SetResolution() function. This function can also be used later to resize the hierarchical depth buffer, causing it to be re-allocated. Note that the resolution width must be a multiple of 8, and the height a multiple of 4. This is a limitation of the occlusion culling algorithm. After setting the resolution we can start rendering occluders and performing occlusion queries. We must first clear the hierarchical depth buffer. Optional The SetNearClipPlane() function can be used to configure the distance to the near clipping plane to make the occlusion culling renderer match your DX/GL renderer. The default value for the near plane is 0 which should work as expected unless your application relies on having onscreen geometry clipped by the near plane.