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Optimized Effects for Mobile Devices

Optimized Effects for Mobile Devices. Ed Plowman, Director of Performance Analysis, ARM Stacy Smith, Senior Software Engineer, ARM . Grab Your Crystal Balls. Top 3 questions I get asked: Q. What does the future of mobile content look like?

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Optimized Effects for Mobile Devices

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  1. Optimized Effects for Mobile Devices Ed Plowman, Director of Performance Analysis, ARM Stacy Smith, Senior Software Engineer, ARM

  2. Grab Your Crystal Balls • Top 3 questions I get asked: • Q. What does the future of mobile content look like? • A. That depends on how much GPU capability you have? • Q. How much performance will content developers need? • A. As much as you can give them! • Q. When will the mobile reach console quality? • Well, lets take a look at that and see if we can answer the others along the way…

  3. Mobile GPU Compute Year On Year Sate of the Art Desktop PS3 Xbox 360 Sate of the Art Mobile

  4. Mobile GPU BW Growth Year on Year Sate of the Art Desktop PS3 Xbox 360 Sate of the Art Mobile

  5. Why is BW Not Progressing as Fast? • Simple… Power! • I did the graph, but desktop GPU power is too horrific! • Desktop = 170 Watts to >300 Watts… that’s just the GPU! • Console = 80-100 Watts (CPU/GPU/WiFi/Network) • Mobile Platform = 3 - 7 Watts (CPU/GPU/Modem/WiFi)!

  6. How to Get 100W of Work from 3Watts? “I believe the sign of maturity is accepting deferred gratification.” - Peggy Cahn • Five main suppliers of GPU tech in mobile • Three are deferred renderers • And those three make up >90% of the volume • This is not a coincidence! • Deferred rendering is most efficient GPU tech for Mobile • Efficiency of BW, HW resource and Power • Getting the most from it requires slightly different thinking…

  7. Thinking in a Deferred World… • Minimize draw calls and state changes • Draw Calls/API calls are not free use them wisely • Grouping draw calls with like state = good • But… don’t go crazy • Large object batches with high potential occlusion can be costly • Remember those vertices still need processing • Draw Target Bind/unbind on each draw call = bad • Seen (disappointingly) in a lot of commercial engines • Can cause flush and reload cycles of tile/cache memory • Bind it once, issue all draw calls, unbind it… • Hint: Take a look at the use of glDiscardFramebufferEXT() • Indicates to driver that render attachment is done with/complete

  8. Thinking in a Deferred World… • Use Vertex Buffer Objects • Client side vertex buffers use copy on write (CoW) on each Draw Call • VBO’s don’t, so they provide a considerable performance increase • Avoid dynamic VBO or IBO updates using glBufferSubData() • Multiple Render Targets (New for OpenGL® ES 3.0) • Very efficient on deferred GPU • Make sure sum of bits/frag is “do-able” “in tile” for max performance • Different criteria for each GPU provider

  9. Avoiding Blocking Behaviours • Deferred GPU’s use a pipeline • glReadPixels(), glCopyTexImage(), glTexSubImage() = bad… • If you must use glReadPixels use PBO’s • Use FBO instead of glCopyTexImage() • Also Occlusion Query (OpenGL ES 3.0)- Results delayed by 1-2 frames • Busy waiting on OQ bad idea!

  10. Make Every Access Count • Think about “cacheability” of data • De-interleave vertex data • Think about representation • Do you really need a FP32/component for a texture coordinates accessing a 512x512 texture? X Y Z W RGB TexCord Vertex = Vert 0 Vert 1 Cache line 1 = Vert 2 Vert 3 Cache line 2 = Vert 1 (XYZW) Vert 3 (XYZW) Vert 0 (XYZW) Vert 2 (XYZW) Cache line 1 = (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) (RGB) Cache line 2 = Tex Cord Tex Cord Tex Cord Tex Cord Tex Cord Tex Cord Tex Cord Tex Cord Cache line 3 =

  11. Compress, Compress, Compress! • ASTC = Adaptive Scalable Texture Compression • New texture compression standard developed by ARM, adopted by Khronos • KHR_texture_compression_astc_ldr for OpenGL ES and Open GL • Increased quality and fidelity at low bit-rates • Expansive range of input formats offers complete flexibility • Choice of base format, 2D and 3D plus addition of HDR formats

  12. Compression in the Pre-ASTC World BC6 64 HDR RGB+A 64 HDR RGBA All Major Players 48 HDR XY+Z 48 HDR RGB ETC, BC2 BC3, BC7 32 HDR X+Y PVRTC PVRTC 32 RGB+A RBGA 32 Input bits/pixel ETC, BC1 BC7 Input Color Formats 24 XY+Z 24 RGB ETC, BC5 16 HDR L 16 X+Y ETC, BC4 16 LA 8 L 1 2 3 4 5 6 7 8 Compressed bits/pixel

  13. ASTC Choices All ASTC 64 HDR RGB+A 64 HDR RGBA 48 HDR XY+Z 48 HDR RGB 32 HDR X+Y 32 RGB+A RBGA 32 Input bits/pixel Input Color Formats 24 XY+Z 24 RGB 16 HDR L 16 X+Y 16 LA 8 L 1 2 3 4 5 6 7 8 Compressed bits/pixel

  14. Look it up or Calculate it? • Shader Features: • Paletted color mapping • Environment mapping • Bump mapping • Variable reflectance mapping • Diffuse falloff of the texture color • Adjustable bump map strength • Adjustable color table • You would be surprised what you can get done in a cycle… precision mediump float; varying vec4 detailtc_envtc, bumptrans; uniform sampler2D dettex, envtex, colormap; uniform float color_param, bumpstrength; void main() { vec4 bt = bumptrans; vec2 bt_crossmul = bt.xy * bt.wz; float diffuse = max(0.0, bt_crossmul.x-bt_crossmul.y); vec4 bump_cr = texture2D(dettex,detailtc_envtc.xy); vec4 tbump = bt * bumpstrength * bump_cr.xyxy; vec2 envtc = tbump.xy + tbump.zw + detailtc_envtc.zw; vec4 col = texture2D(colormap, vec2(bump_cr.z, color_param)); vec4 env = texture2D(envtex,envtc); gl_FragColor = col * diffuse + env * bump_cr.w; } Mali-T600 series = 3 Cycles

  15. GDC 2012 Demo: Timbuktu

  16. Asset Conditioning • Cross platform - desktop & mobile • Desktop build - caching • Mobile build - loads caches • Asset pipeline - utility functions

  17. Batching • Deferred immediate mode rendering • glDrawElements and glDrawArrays have an overhead • Less draw calls, less overhead. • DrawCall class stitches multiple objects into one draw • Macro functions in shaders make batching as simple as: vec4 pos=transform[getInstance()]*getPosition();

  18. Batching

  19. Batching uniform mat4 transforms[4];

  20. Object Instancing • Multiple geometries, or single object instances: for(inti=0;i<50;i++) drawbuilder.addGeometry(geo1); drawbuilder.Build() • Can implement LOD switching, when objects are sorted front to back and correctly culled. • Seen in TrueForce

  21. Special Effects

  22. Special Effects: Bloom

  23. Special Effects: Bloom • When considering uses of greater colour resolution the first thought was HDR and Bloom. • But how to do bloom without the HDR images?

  24. Special Effects: Bloom

  25. Special Effects: Bloom Render to low res FBO mapped to texture Value filter and blur in 1st post- processing pass, onto second FBO texture Sample vertical blur in second pass then apply to full resolution frame buffer

  26. Special Effects: Depth of Field

  27. Special Effects: Depth of Field • 16bit depth buffers as textures opened the possibility of a variable blur for depth of field • But how to do it without 16bit textures?

  28. Special Effects: Depth of Field

  29. Special Effects: Depth of Field Mix Bloom Additive

  30. Special Effects: Terrain Mapping

  31. Special Effects: Terrain Mapping • Uniform Buffers and Vertex IDs can be used to implement tessellated mesh subdivision • But how can this be approximated without the buffers or IDs?

  32. Special Effects: Terrain Mapping

  33. Special Effects: Terrain Mapping

  34. SIGGRAPH 2012 Demo: Timbuktu 2

  35. Timbuktu 2: Extended features • OpenGL® ES 3.0! • 3D textures • Shadow comparison • 16 bit depth textures • HDR lighting

  36. 3D Textures • Give more definition to deformed track • 3D Textures mipmap in all 3 dimensions • Instead used 2D Texture arrays

  37. 3D Textures texture2DArray floor(z) fract(z) ceil(z) mix(t1, t2, frac)

  38. Shadow Mapping • Depth rendered to FBO from viewpoint of light • Projected onto scene to compare to distance • Doing this in the shader yields some interesting results

  39. Shadow Comparison Texture OpenGL ES 2.0 Texture Compare: Interpolate Compare OpenGL ES 3.0 Shadow Texture Compare: Compare Compare Compare Compare Interpolate

  40. 16 Bit Depth Buffers • Also used for: • Soft Particles • Better fidelity of DOF

  41. Particle Lighting • Displacement Mapping: • Texture offset to X and Y coords • Distortion strength increases over time

  42. HDR Lighting • RGBA 10 10 10 2 format used • Everything gets normalised • Bright spots need to stand out • Make everything else darker! • Set exposure in post processing

  43. Main conference ARM Sponsored Sessions

  44. ARM #1124 in-booth Educational Theater • Over 30 talks from ARM and partners such as EpicGames, Havok, PlayJam, Geomerics, Softkinetics, Metaio, Marmalade • 20 minute length talks with Q&A at the end • An Android tablet prize draw at each session • Summary and videos of all Educational Theater Talks at http://malideveloper.arm.com/gdc2013

  45. Thank you Any questions? malideveloper.arm.com

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