Gamedev: Multi-threaded animate model
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This document discusses a multithreading technique for accelerating the rendering of animated 3D models. It describes using multiple threads to independently animate different 3D models in parallel to take advantage of multicore CPUs. Each model has double buffers to allow simultaneous skinning and rendering by different threads. Updating models intermittently instead of every frame reduces bandwidth usage and allows more parallel processing.
Gamedev: Multi-threaded animate model
- 2. Multithreading solution to accelerate rendering for animated 3D models. Relevant techniques : Level of detail of mesh and skeleton. SIMD extension instruction. GPU based (vertex shader) calculation – models are offloaded to video memory. Skeleton animation – bone structure and pose transform. Animate bone to animate model – vertices are influenced by parent bones (maybe > 1).
- 3. Animation pipeline has massive matrix calculations. Bone positioning (transforms), vertex positioning (skinning). Animated models are independent. Not all models have to be updated for animation every frame. Intermittently update reduces bus traffic, improves parallelism between CPU and GPU, and void redundant calculations.
- 4. Modules: thread pool, double buffering, main thread (rendering call).
- 5. Send the model to be animated into the pool for multi-threading. Store number of models in the thread pool, g_iNumModelsInPool, accessed by the main thread. If g_iNumModelsInPool = 0, models are completely animation updated and ready for drawing.
- 6. Allow simultaneous skinning and rendering. Each model is given two buffers for skinning. Read buffer with ready data for main thread to draw. Write buffer with next frame data written by the animation thread. Lifetime for each buffer, avoid unready or too old skinning data. Animation thread accesses valid skinned data in the read buffer for other parallelism (collision …).
- 7. Bus bandwidth for uploading data to video memory is a bottleneck. Update interval of frames, g_iUpdateInterval, controls the frequency of animation updates. Lower interval yields more frequent (smooth) animation and more computations. Higher interval yield less frequent (slower) animation and less computations. Data do not have to be uploaded to video memory every frame.
- 8. Bones compose the skeleton. Mesh (vertices) attached to bones compose the skinned model. Vertex positions are relative to its parent bones with weights. See red vertex in the following figure.