OpenGL ES 3.0 – Creating the Soft Kitty Demo

Kristof Beets

Director of Business Development – PowerVR Graphics

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Soft Kitty Demonstration Designed for PowerVR Series6 GPU Cores – Demo Video

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Animating Soft Kitty

Vertex Skinning animates a character using a Bone Structure

Each vertex is influenced by a number of bones - typically 3 to 4 bones

By animating the bones (skeleton) the vertices are moved and the object animated

Cats are highly flexible creatures – 4 bones were insufficient to obtain realistic animation

12 Bones per Vertex required to avoid artefacts in the animation of the Cat Model

3 to 4 times higher workload than typical game animation shader code

Vertex Skinning with 12 Bones Influencing Each Vertex

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Adding Fur to Soft Kitty

Approximate Fur by rendering multiple shell layers with dotted texture

Dots will connect and form the individual strands of hair forming the fur

More layers increase the quality of the effect – high alpha blended fillrate required

Shell Based Fur Effect

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Optimising Soft Kitty – Transform Feedback

What is Transform Feedback ? Benefit for Soft Kitty ?

Transform feedback allows vertex shader output to be written out to memory

Complex vertex shader work is only done once and then cached in memory

Following passes use cached data from memory avoiding costly recalculation

Reduced vertex shader workload and increased performance

Execute Expensive Vertex Skinning Animation Only Once

Execute Once

Use Many

Cat Geometry

Vertex Shader

Cat Animated Pose Memory

Render Passes

Shadow

Fur Shells

Transform Feedback

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Optimising Soft Kitty - Instancing

What is Instancing ? Benefit for Soft Kitty ?

Instancing allows the same vertex buffer to be drawn multiple times in a single API call

Each instance can be drawn with different settings e.g. scale, position, etc.

Avoids multiple API state changes thus reducing CPU loading

Helps reduce the CPU loading of the demonstration improving power efficiency

Single Draw Call for the Fur Effect

Versus SetState()

DrawInstanced()

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The Soft Kitty Render Loop Overview of Render Passes

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PVRTune View of Soft Kitty GPU Fully Loaded – No Idle Time Gaps – Vertex Processing Limited Workload

Shadow Render

Horizontal Blur Vertical Blur Final Render

Transform Feedback Animation

Shadow Render

Horizontal & Vertical Blur

Final Render

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Future Demo Sessions – Series6XT and 7XT PowerVR Rogue Planet and PowerVR Library

PowerVR Rogue Planet

Hardware Tessellation for Terrain Rendering

PowerVR Library

Physically Based Rendering

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Soft Kitty – Bloopers… Development Issues… Small shader mistakes… big impact

PVRTrace is the ideal tool to help figure out these issues…

OpenGL ES 3.0 – Creating the Soft Kitty Demo

Kristof Beets

Director of Business Development – PowerVR Graphics