Advanced Ambient Occlusion Methods for Modern Games Andrei Tatarinov, Senior Developer Technology Engineer Alexey Panteleev, Senior Developer Technology Engineer Outline • What is AO and why is it SS? • Is screen space enough? • HBAO+ Ultra • Voxel Ambient Occlusion • VXAO integrations gameworks.nvidia.com 2 Screen Space Ambient Occlusion gameworks.nvidia.com 3 Screen Space Ambient Occlusion • A rendering technique for efficiently approximating ambient occlusion in the games • Independent from scene complexity • Minimal data pre-processing • Easily integrated into any modern rendering pipeline – Don’t do this… © Wikipedia » Or this gameworks.nvidia.com 4 Horizon-Based Ambient Occlusion + • Bavoil, L., Sainz, M., Image-Space Horizon- Based Ambient Occlusion, Siggraph 2008 • HBAO+ improves upon existing Ambient Occlusion techniques to add richer, more detailed, more realistic shadows around objects that occlude rays of light • Compared to previous techniques, HBAO+ is faster, more efficient, and significantly better gameworks.nvidia.com 5 Is screen space enough? gameworks.nvidia.com 6 Is screen space enough? • No. – Don’t do this… » Or this gameworks.nvidia.com 7 Is screen space enough? • No. • Let’s do an excursion into history… – Don’t do this… » Or this gameworks.nvidia.com 8 Assassin’s Creed series • Strategic partnership between NVIDIA and Ubisoft • GameWorks is featured in three major installments – Don’t do this… » Or this gameworks.nvidia.com 9 Assassin’s Creed IV Black Flag • Towns look like chaotic collections of buildings • Objects are fairly far away from each other Image courtesy of Ubisoft gameworks.nvidia.com 10 Assassin’s Creed Unity • People are always protesting on the streets and squares Image courtesy of Ubisoft gameworks.nvidia.com 11 Assassin’s Creed Syndicate • XIX century London brings some order to the crowd Image courtesy of Ubisoft gameworks.nvidia.com 12 Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 13 gameworks.nvidia.com 14 What’s gone wrong? • Let’s take a simple scene gameworks.nvidia.com 15 What’s gone wrong? • This is how AO would look like: gameworks.nvidia.com 16 What’s gone wrong? • Let’s try to add a character walking by: gameworks.nvidia.com 17 What’s gone wrong? • Let’s try to add a character walking by: gameworks.nvidia.com 18 What’s gone wrong? • Let’s try to add a character walking by: gameworks.nvidia.com 19 What’s gone wrong? • We want minimal influence of the character on the AO image gameworks.nvidia.com 20 What’s gone wrong? • AO looks correct if character is close enough gameworks.nvidia.com 21 What’s gone wrong? • HBAO+ detects objects not belonging to a surface • Samples from these objects are not taken into account • HBAO+ doesn’t know what is behind the character gameworks.nvidia.com 22 What’s gone wrong? • HBAO+ detects objects not belonging to a surface • Samples from these objects are not taken into account • HBAO+ doesn’t know what is behind the character gameworks.nvidia.com 23 What’s gone wrong? • HBAO+ detects objects not belonging to a surface • Samples from these objects are not taken into account • HBAO+ doesn’t know what is behind the character gameworks.nvidia.com 24 What’s gone wrong? • HBAO+ detects objects not belonging to a surface • Samples from these objects are not taken into account • HBAO+ doesn’t know what is behind the character gameworks.nvidia.com 25 What’s gone wrong? • HBAO+ detects objects not belonging to a surface • Samples from these objects are not taken into account • HBAO+ doesn’t know what is behind the character gameworks.nvidia.com 26 What’s gone wrong? • HBAO+ detects objects not belonging to a surface • Samples from these objects are not taken into account • HBAO+ doesn’t know what is behind the character gameworks.nvidia.com 27 What’s gone wrong? • This results in visible “halo” around the character gameworks.nvidia.com 28 What’s gone wrong? • This results in visible “halo” around the character gameworks.nvidia.com 29 Tune HBAO+ • Use smaller HBAO+ radius • Minimizes artifacts, not removes them! • Makes AO look worse gameworks.nvidia.com 30 Tune HBAO+ • Use smaller HBAO+ radius • Minimizes artifacts, not removes them! • Makes AO look worse gameworks.nvidia.com 31 Need a Superman • Want to teach HBAO+ see through objects – Don’t do this… » Or this Image from SuperFriends gameworks.nvidia.com 32 Need a Superman • Want to teach HBAO+ see through objects • Bavoil, L., and Sainz, M., Multi-Layer Dual-Resolution Screen-Space Ambient Occlusion, Siggraph 2009 • Mara, M., McGuire, M., Luebke, D., Lighting Deep G-Buffers: Single- Pass, Layered Depth Images with Minimum Separation Applied to Indirect Illumination, NVIDIA 2013 Image from SuperFriends gameworks.nvidia.com 33 Depth-peeled AO • Good solution to a problem gameworks.nvidia.com 34 Depth-peeled AO • Good solution to a problem • AO shaders become more sophisticated • Integrating into an engine may be troublesome gameworks.nvidia.com 35 Depth-peeled AO • Good solution to a problem • AO shaders become more sophisticated • Integrating into an engine may be troublesome • Do we really need full-scale depth peeling? gameworks.nvidia.com 36 Double-layered AO • Only moving objects create noticeable artifacts! • Use two layers to separate statics from dynamics • AO shaders stay the same gameworks.nvidia.com 37 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 38 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 39 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions First pass is static geometry only gameworks.nvidia.com 40 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Second pass is static geometry plus characters gameworks.nvidia.com 41 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Use stencil to mask out the characters gameworks.nvidia.com 42 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Use stencil to mask out the characters gameworks.nvidia.com 43 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions And blit them on the first pass AO image gameworks.nvidia.com 44 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions AO from characters is missing gameworks.nvidia.com 45 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Use inverted stencil gameworks.nvidia.com 46 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Use inverted stencil and MIN blending gameworks.nvidia.com 47 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Single-layered HBAO+ gameworks.nvidia.com 48 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Double-layered HBAO+ gameworks.nvidia.com 49 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions Single-layered HBAO+ gameworks.nvidia.com 50 gameworks.nvidia.com 51 gameworks.nvidia.com 52 gameworks.nvidia.com 53 Integration into Assassin’s Creed Syndicate • Tune HBAO+ to look good in all cases • Pick AO radius optimal to handle both small features and large-scale objects • …and minimize artifacts gameworks.nvidia.com 54 Integration into Assassin’s Creed Syndicate • Tune HBAO+ to look good in all cases • Pick AO radius optimal to handle both small features and large-scale objects • …and minimize artifacts • But hey, we’re running two passes now! gameworks.nvidia.com 55 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 56 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 57 Integration into Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 58 Assassin’s Creed Syndicate • AO-only video with massive corruptions gameworks.nvidia.com 59 HBAO+ Ultra • Double-pass HBAO+ is default in Ultra preset • Decided to name it “HBAO+ Ultra” • Added advanced blending functionality to HBAO+ gameworks.nvidia.com 60 Advanced blending functionality in HBAO+ struct GFSDK_SSAO_TwoPassBlend_D3D11 { // When enabled, overrides any other compositing state GFSDK_SSAO_BOOL Enable; // Used to mask the pixels in each of the 2 passes ID3D11DepthStencilView* pDepthStencilView; // Blend & depth-stencil state for the first compositing pass GFSDK_SSAO_BlendPass_D3D11 FirstPass; // Blend & depth-stencil state for the second compositing pass GFSDK_SSAO_BlendPass_D3D11 SecondPass; GFSDK_SSAO_TwoPassBlend_D3D11() : Enable(false) , pDepthStencilView(NULL) { } }; gameworks.nvidia.com 61 gameworks.nvidia.com HBAO+ 62 gameworks.nvidia.com HBAO+ Ultra63 gameworks.nvidia.com HBAO+ 64 gameworks.nvidia.com HBAO+ Ultra 65 gameworks.nvidia.com HBAO+ 66 gameworks.nvidia.com HBAO+ Ultra 67 gameworks.nvidia.com HBAO+ 68 gameworks.nvidia.com HBAO+ Ultra69 gameworks.nvidia.com HBAO+ 70 gameworks.nvidia.com HBAO+ Ultra71 gameworks.nvidia.com HBAO+ 72 gameworks.nvidia.com HBAO+ Ultra73 Performance 6 • GeForce GTX 970 4.8 MS 5 • 1920x1080 4 3 2.1 MS 2 1 0 HBAO+ HBAO+ Ultra gameworks.nvidia.com 74 Summary • Screen space is not enough for robust AO • You need just two layers to improve quality • HBAO+ supports advanced blending modes • HBAO+ source will be available to registered developers gameworks.nvidia.com 75 Huge thanks to • Louis Bavoil, NVIDIA • Maksym