GPU Coding

In Unity

teadrinker.github.io/gpu-coding-in-unity

download gpu-coding-in-unity unity project

download camera-bound-test bound unity project

Martin Eklund

  meshFilter.mesh = CreateQuadMesh(
    4.5f,  // car should be around 4 meters
    0.1914063f, 0.08691406f, // the size of each sprite
    Random.Range(0,5), Random.Range(0,10) // randomize car sprite
  );
  
  // randomize depth value
  currentPosZ = Random.value * depth; 
  // initialize the speed for this car
  currentSpeed = speed * (1.0f - speedVariation * Random.value); 
  // initialize position for this car
  currentPosX = (Random.value - 0.5f) * width; 

  currentPosX += currentSpeed * Time.deltaTime;
  if(currentPosX > width/2) {
  	currentPosX = -width/2;
  }
  
  transform.localPosition = new Vector3(currentPosX, 0.0f, currentPosZ);

GPU Time!

  Properties {
    _MyVariable  ("My Variable", Range(1,10)) = 4
  }

  float _MyVariable;  // accessible from the material gui
  
  v2f vert (appdata v) 
  {
    // do this per vertex
  }
  
  fixed4 frag (v2f i)
  {
    // do this per pixel
  }

• We don't have a "object callback", our shader code runs per vertex

  - Use vertex shader, just redo the same work for each vertex

• When processing a vertex, we don't know which object/quad we are processing

  - Use z-value

• There is no random function on GPU

  - Use hash funtion + a unique value per object

• You cannot write to variables in the code (just output vertex or color data)

  - Rewrite the code so it doesn't need state

  // init
  currentPosX = (Random.value - 0.5f) * width; 

  // update
  currentPosX += speed * Time.deltaTime;

  // no init needed


  // update
  float initialPosX = (floatHash(uniqeValueForThisCar) - 0.5f) * width;
  float posX = initialPosX + speed * timeInSeconds;

  // no init needed


  // update
  float initialPosX = (floatHash(uniqeValueForThisCar) - 0.5f) * width;
  float posX = initialPosX + speed * timeInSeconds;
  posX = (posX + width/2.0f) % width - width/2.0f; // wrap around

v2f vert (appdata v) // unity vertex shader
{
  v2f o;
  
  float4 pos = v.vertex; 
  float uniqeValueForThisCar = pos.z;
  float timeInSeconds = _Time[1];

  pos.z *= _depth; // don't randomize depth, this will ensure they are drawn back to front
   
  float speed = _speed * (1.0 - _speedVariation * floatHash(uniqeValueForThisCar+1.0));
  
  float initialPosX = (floatHash(uniqeValueForThisCar) - 0.5f) * _width;
  float posX = initialPosX + speed * timeInSeconds;
  posX = (posX + _width/2.0f) % _width - _width/2.0f; // wrap around
  
  pos.x += posX; // offset quadvertex by car position

  o.vertex = mul(UNITY_MATRIX_MVP, pos);

  return o;
}   

The GPU shader in the unity project also does:

• Size and aspect-ratio of quad
• Height support for flying cars
• A simple lighting calculation
• Randomization of sprite selection

• Calculation of uv coordinates

  And it is still around 10 times faster than the C# version!

Setting up a new unity project for Gear VR

Anti-aliasing

Try increasing Anti Aliasing in Project Settings/Quality.