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ScreenSpace AABB from bounding sphere for Clustered Shading

Michael SEGURA · 2022-01-23T12:00:57

Hello!I always used this code based from Intel code to compute the Screen Space AABB from the Bounding Sphere.It's based from this sample code:https://www.intel.com/content/www/us/en/developer/articles/technical/deferred-rendering-for-current-and-future-rendering-pipelines.html void UpdateClipRegionRoot(in float nc, in float lc, in float lz, in float Radius, in float CameraScale, inout float ClipMin, inout float ClipMax) { float nz = (Radius - nc * lc) / lz; float pz = (lc * lc + lz * lz - Radius * Radius) / (lz - (nz / nc) * lc); if (pz > 0.0f) { float c = -nz * CameraScale / nc; if (nc > 0.0f) ClipMin = max(ClipMin, c); else ClipMax = min(ClipMax, c); } } void UpdateClipRegion(in float lc, in float lz, in float Radius, in float CameraScale, inout float ClipMin, inout float ClipMax) { float rSq = Radius * Radius; float lcSqPluslzSq = lc * lc + lz * lz; float d = rSq * lc * lc - lcSqPluslzSq * (rSq - lz * lz); if (d > 0.0f) { float a = Radius * lc; float b = sqrt(d); float nx0 = (a + b) / lcSqPluslzSq; float nx1 = (a - b) / lcSqPluslzSq; UpdateClipRegionRoot(nx0, lc, lz, Radius, CameraScale, ClipMin, ClipMax); UpdateClipRegionRoot(nx1, lc, lz, Radius, CameraScale, ClipMin, ClipMax); } } void ComputeClipRegion(in float3 Center, in float Radius, out float4 ClipRegion) { ClipRegion = float4(1.0f, 1.0f, 0.0f, 0.0f); if ((Center.z + Radius) >= CameraNear) { float2 ClipMin = float2(-1.0f, -1.0f); float2 ClipMax = float2(+1.0f, +1.0f); UpdateClipRegion(Center.x, Center.z, Radius, Projection[0].x, ClipMin.x, ClipMax.x); UpdateClipRegion(Center.y, Center.z, Radius, Projection[1].y, ClipMin.y, ClipMax.y); ClipRegion = float4(ClipMin, ClipMax); } } void ComputeBoundingBox(in float3 Center, in float Radius, out float4 Bounds) { ComputeClipRegion(Center, Radius, Bounds); Bounds = 0.5f * float4(Bounds.x, -Bounds.w, Bounds.z, -Bounds.y) + 0.5f; } It works very good but I wonder if there is a more modern and efficient way to do it?Something to note is you have Point Light, Spot Light, Tube Light and Rect Light in lighting calculations.I actually compute the bounding sphere in all these types so it's not the most possible efficient way.But for point light in all cases you would need a Sphere to Screen Space AABB.Thanks a lot for all the help and resources about this topic!If you can recommend another way for the sphere to screen space AABB, it's very welcome too!