© Copyright Khronos Group, 2006 - Page 1 Shaders Go Mobile: An Introduction to OpenGL ES 2.0 Tom...

© Copyright Khronos Group, 2006 -

Shaders Go Mobile: An Introduction to OpenGL ES

2.0

Tom Olson, Texas Instruments Inc.

2TI Proprietary Information

About Texas Instruments

A Strong Supporter of Standards Khronos Promoting Member Active in OpenGL ES, OpenMAX, OpenKODE

The Leader in Semiconductors for Wireless #1 in wireless revenue (Dataquest) #1 in digital basebands (Forward Concepts 2006)

Over 2B handsets shipped

#1 in wireless application processors (FC 2006) Over 90M OMAP processors shipped


Outline

Introduction to OpenGL ES•What it is•Design principles•Versions and status

OpenGL ES 2.0•What’s different about the API•What’s different about the shading language

Status•…and where to go for more information


What is OpenGL ES?

The Leading 3D Graphics API for Mobile Devices• Defined by the Khronos Group• Created with blessing and cooperation of the OpenGL ARB• Subset of Desktop OpenGL •…with a few well-chosen mobile-specific extensions

Design Goal• Deliver most of the power of OpenGL•…but in a much smaller package

Design Principles• Eliminate redundancy - one way to do things• Eliminate rarely used, legacy, or expensive features• Eliminate features not used in games


Overview of OpenGL ES 1.xFeatures removed from desktop OpenGL• Begin/End - vertex arrays & buffers only• Fancy features: imaging subset, evaluators, display lists• Legacy features: color index, DrawPixels• Double precision data types & entry points

Almost everything else is still there!• Vertex Transforms & Lighting (mostly)• Multi-texturing (2D only)• fsAA via Multisampling• Basic blending

Features added• Fixed-point and byte data• Fixed-point only profile available


OpenGL ES Versions

OpenGL ES 1.1•Spec released at SIGGRAPH 2004•Adopted as standard in many mobile OSes•Hardware accelerated ES 1.1 shipping in volume•The ‘sweet spot’ for high-end mobile phone content today

OpenGL ES 2.0•Final spec to be released in 4Q 2006•The ‘sweet spot’ in 200?


Why OpenGL ES 2.0?

Doom 3’s Zombies

Far Cry’s Water

Unreal’s Rocks

Halo’s Ice

Cause shaders are so cool…


OpenGL ES 2.0 Key Changes

Add:•Vertex and Fragment Shaders•ES Shader Language (GLSL ES)•Option for off-line compilation (binary shaders)

Remove•Anything you can do in a shader• Fixed function transform and lighting• Fixed function texturing, fog, etc.

•That’s right - 2.0 is NOT backward compatible with 1.x!• But, ES 2.0 HW can support an ES 1.x driver


FragmentProcessor

Vertex Processor

xform

xform

xform

Light

Vtx Coords

Normals

Colors

TexCoords

Primitive assembly

CullClip

Viewport

Rasterize

Z-testStencilScissor Blend

VERTICES TRIANGLES FRAGMENTSAPPLICATION

State VectorState cmds

Input

Indices

Attribute 0

…

…

Attribute n-1

tex0

tex1

fog

What Changes From ES 1.1 to ES 2.0?• General-purpose attributes replace fixed input arrays• Vertex shader programs replace transform and lighting• General-purpose uniforms replace fixed lighting & texture state• General-purpose varyings replace fixed fragment attributes• Fragment shader programs replace texture / fog / alpha test

The OpenGL ES 2.0 Pipeline


Other Features Added to ES 2.0Texture Features• Cube Maps• Minimum of eight texture units

Frame Buffer Objects• Simplified version of EXT_frame_buffer_object• Mandated minimum configuration support

Per-Fragment Ops• Stencil buffer support is required• BlendEquation and BlendEquationSeparate supported (mostly)

Point Sprites• Regular GL points removed


Optional FeaturesOptional ETC Texture Compression• IP contributed by Ericsson

NPOT Textures

3D Textures

Visibility Queries

Half Float Data

Float / Half Float Textures


The ES Shader Language

GLSL ES is very similar to GLSL, but…•No fixed function attributes• glVertex, glMultiTexCoord<n>, glColor…

•No fixed function Uniforms• glModelViewMatrix, glLight[i], …

•Predefined varyings are still there• Vertex shader must write glPosition• Fragment shader can read glFragCoord• Fragment shader must write glFragColor


Precision Qualifiers GLSL ESRange of precisions• Low - range [-2,2] with 8 bits precision•Medium - range [-214,214] with 10 bits precision•High - range [-262,262] with 16 bits precision•Can declare per variable, or declare a default precision

Examples•lowp vec4 color;•highp vec3 LightPosition;

Defaults•Vertex Shader variables default to high precision•Fragment Shader has no default - MUST declare


Other Changes to GLSL ES

Invariance•Optimization may affect value of expressions•Handled in Desktop GLSL by ftransform()•Handled in GLSL ES by invariant keyword

No Virtualization•Valid programs may fail to compile due to resource limits•Conformance test will enforce reasonable capability•Any OpenGL ES 1.1 state should compile


Conclusion

OpenGL ES 2.0 is coming•Full vertex and fragment shader support for mobile devices•Small, clean API thanks to elimination of fixed functionality

For more information•Draft specs at http://www.khronos.org/opengles/2_X/•Final specification coming soon!

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