Bring AAA graphics to mobile platforms

-



Hardware: ImgTex SGX GPU
Software: how to bring console graphics to mobile platform.

Shaders, RTT, depth texture , MSAA

Architecture
- tile-based deferred rendering GPU (ARM Mali, SGX)

Tiled -based
- split the screen into tiles, 16x16 or 32x32 pixels

GPU fits an entire tile on chip - doesn't have frame buffer memory

Process all draw calls for one tile
 - repeat each tile

Each tile is written to memory as all finished

Vertex frontend
  vertex primitives to GPU cores
     - split vertex

vertex preshader:  fetch input data ( attribute and uniforms)
vertex shader: Universal scalable shader engine, the same for the pixel 
             - mutli-thread

Tiling:
   Optimizes vertex shader output
    Bins resulting primitives into tile data

parameter buffer
- stored in sys. memory
- don't want to overflow buffer!! ( will need to flush )

Pixel frontend


- reads parameter buffer ( reading tile data from vertex processing)
-distribute  to all cores
   - one tile at a  time
  - a tile is in full one core
  - process all tiles until finish


Pixel setup
- receive tile commands 
- fetch vertex shader
-triangle rasterization
- Hidden surface removal- depth, stencil test

Pixel pre shader
- fills in interpolator and uniform data
- kicks off non-depdendent data
Pixel shader
- multi thread ALUs
-each thread can be vertex or pixel;
- multiple USSEs in each GPU core

Pixel backend
 - trigger when all pixel in tiles are done
- performs data conversions, MSAA
- write finish.

Shader Unit Caveats


- without dynamic flow-control
- with dynamic flow-control

Alpha-blending
- not separate specialize GPU

Mobile is the new PC
- wide feature and performance range
-scalable graphics
-user graphics setting
     - low/med/high/ultra
     - render buffer size scaling

Render target is on die
 - MSAA is cheap and use less memory
  - only data in RAM
 - Have 0-5 ms cost
  - Be wary of buffer restores ( color or depth)

 - see usage case for shadows

No bandwidth cost for alpha blending

Free hidden surface removal

Mobile vs Console
 - very large CPU overhead for OpenGLES API
     - max CPU usage at 100-300 draw calls

- avoid too mush data per scene

- shader patching
   - reduce render state change


Alpha test / discard
 - conditional z write is very slow

Render buffer management
 - each RT is a whole new scene
 - avoid switchRT back and forth
 - can cause a new restore 
 -                     new resolve

- avoid buffer restore
  - clear everything, color depth stencil
 - a clear just set some dirty bits in register

  - avoid buffer resolve
 - use discard extension discard_framebuffer

unnecessary different FBO combos
  - don't let driver think it needs to start resolving and restoring any buffers~~!!!

texture lookups
   - don't perform texture lookups in pixel shader
 - let pre shader queue then up ahead of time
- don't compute texture coordinate with math

don't use .zw components for texture coordinate

mobile shader material system: original is too complicated

Mobile material shaders
  - separate shader by mobile
 - Lots of #ifdef

Shader Offline processing
- Run C pre-processor offline
 - reduce ingame copile time
 - eliminate duplicates at offline time

Shader compiling
 - compile all shaders at startup
 - avoids hitching at runtime
- compile on GL thread, while loading on game thread
 - compiling is no enough
   - must issue dummy draw calls
   - how certains states affect shaders
 - avoid shader....??


God Rays on mobile
 - fewer texture fetch

optimize for mobile
  - move all math to VS
  - pass down data through interpolation
-  split radial filter into 4 draw calls: 4x 8 = 32 texture lookups  ???
 - from 30ms to 5 ms

God rays
 - 1st pass
  - 2nd pass
  -3rd
  - 4th
  - 5th
  -6th







Character shadows
  port from xbox
 - projected , modulate dynamic shadow
 - compare scene depth and character depth
  - draw character on top ( no self-shader)

shadow optis
 - shadow depth
    - avoids RT switch ( resolve & restore)
 - Resolve sceneDepth just before shadows*
    - write out tile depth to RAM to read as texture
    - use glDiscardFrameBuffer to avoid resolve
    -  encode depth in F16 / RGBA8 color
  - Draw screen-space quad instead of cube
      - avoid dependent texture lookup

Tool tips
   - Use an OpenGL ES wrapper on PC
         - Almost WYSIWYG
         - debug on visual studio
   - Apple Xcode GL debugger, iOS 5!
         - full capture of one frame
         -  show each drawcall used by each draw call

Next-Generation
  - ImgTex "Rogue" (6xxx series):
                   20x on graphics
            - 100+ GFLOPS
            - DX10, OGLES Halti


Comments

Post a Comment

Popular posts from this blog

Drawing textured cube with Vulkan on Android

-
Image
Vulkan is a modern hardware-accelerated Graphics API. Its goal is providing an high efficient way in low-level graphics and compute on modern GPUs for PC, mobile, and embedded devices. I am personally working a self training project, vulkan-android , to teach myself how to use this new APIs. The difference between OpenGL and Vulkan OpenGL: Higher level API in comparison with Vulkan, and the next generation of OpenGL 4 will be Vulkan.   Cross-platform and Cross-language (mostly still based on C/C++, but people implemented diverse versions and expose similar API binding based on OpenGL C++, WebGL is a good example).  Mainly used in 3D graphics and 2D image processing to interact with GPU in order to achieve hardware acceleration. Don't have a command buffer can be manipulated at the application side. That means we will be easily see draw calls being the performance bottleneck in a big and complex 3D scene. Vulkan: Cross-platform and low-overhead. Erase the boundary bet...
Read more

Fast subsurface scattering

-
Image
Fig.1 - Fast Subsurface scattering of Stanford Bunny Based on the implementation of three.js . It provides a cheap, fast, and convincing approach to do ray-tracing in translucent surfaces. It refers the sharing in GDC 2011  [1], and the approach is used by Frostbite 2 and Unity engines [1][2][3]. Traditionally, when a ray intersects with surfaces, it needs to calculate the bouncing result after intersections. Materials can be divided into three types roughly.  Opaque , lights can't go through its geometry and the ray will be bounced back.  Transparency , the ray passes and allow it through the surface totally, it probably would loose a little energy after leaving.  Translucency , the ray after entering the surface will be bounced internally like below Fig. 2. Fig.2 - BSSRDF [1] In the case of translucency, we have several subsurface scattering approaches to solve our problem. When a light is traveling inside the shape, that needs to consider the ...
Read more

glTF loader for Android Vulkan

-
Image
This post is going to introduce how we integrate with an existing glTF loader library to make it be able to show glTF models in our Vulkan rendering framework,  vulkan-android . tinygltf In the beginning, we don't want to make our new own wheel, so choosing  tinygltf as our glTF loader. tinygltf is a C++11 based library that would help us support all possible cross-platform project easily. tinygltf setup in Android Studio In  vulkan-android  project, we put third party libraries into third_party folder. Therefore, we need to include tinygltf from third_party folder in app/CMakeLists.txt as below. set(THIRD_PARTY_DIR ../../third_party) include_directories(${THIRD_PARTY_DIR}/tinygltf) Model loading from tinygltf We are going to load a gltf ASCII or binary format model from the storage. tinygltf provides two APIs , they are LoadBinaryFromFile() and LoadASCIIFromFile() respectively based on the extension name is *.glb or *.gltf. TinyGLTF loader will return a tiny...
Read more