Particles_compute

Particles_compute.glsl

/*
Particle system using a compute shader

Author: Tim Gerritsen <tim@mannetje.org> - Go Robot
Date: December 2017
Updated: Februari 2018, added comments

I tried to add as much comments as possible. Hope everything is clear.
If not, try to contact me through touchdesigner slack #glsl, or email.
*/

/* Setting the local size to 16x16, so in total this shader is ran 256 times the dispatch size */
layout (local_size_x = 16, local_size_y = 16) in;

uniform float uTime; 						// Current time in seconds (python: absTime.seconds) to generate random numbers
uniform float uFpsTick; 					// Length of a frame in seconds (1/fps)

uniform int uReset;							// Compute shader will reset all output filters when set to 1
uniform int uParticles;						// Amount of total particles (dispatch size * local size)

uniform vec4 uPositionSizeStart;			// Random range start position xyz and start size 
uniform vec4 uPositionSizeEnd;				// Random range end position xyz and end size

uniform vec4 uDirectionSpeedStart;			// Random range start direction xyz and start speed 
uniform vec4 uDirectionSpeedEnd;			// Random range end direction xyz and end speed 

uniform vec2 uParticleLife;					// Random range start and end lifetime

uniform float uSizeOverLife;				// Alter size over lifetime. When negative decrease the size
uniform float uSpeed;						// Overall speed
uniform vec2 uGravity;						// Amount of gravity direction force and acceleration
uniform vec3 uCollider;            // Collider
uniform vec2 uNoise;						// Amount of noise force amplitude and frequency
uniform float uFloor;						// Floor y position

// Data pixel offsets
#define DATA_LIFE 0
#define DATA_POSITION 1
#define DATA_VELOCITY 2
#define DATA_COLOR 3

// Particle states
#define PARTICLE_STATE_DEAD 0
#define PARTICLE_STATE_ALIVE 1

// Texture inputs
#define TEX_COLOR_LIFERANDOM 0

// Math stuff
#define PI 3.1415926536

// Defining a particle
struct Particle {
	int index;				// Index of the particle (0 to uParticles)
	float lifetime;			// Current particle lifetime in seconds
	float maxlife;			// Initial particle lifetime in seconds
	int state;				// Current particle state (defined above)

	vec3 position; 			// Particle position
	float size;				// Particle size

	vec3 direction;			// The direction the particle is going
	float speed;			// And it's speed

	vec4 color;				// Color of the particle defined by the input texture
};

// Global variables
int gDataSize = 4;	// This size represents the amount of vec4 data types 'fit' in the above struct.
					// So 2 ints and 2 float can be merged together as 1 vec4. (so we can save it as color)

Particle gEmptyParticle = Particle(0,0,0,0, vec3(0),0, vec3(0),0, vec4(0)); // Defining an empty particle 
Particle gParticle;	// This will be set to the current particle

// This generates a 'random' number between 0 and 1
float Hash(vec2 p) { return fract(mod(sin(dot(p,vec2(12.9898,78.233))) * 43758.5453, PI)); } 

// Helper function to transform a particle index and offset to pixel coordinate
// Offset is used to determine which 'vec4' we are fetching from the struct.
ivec2 IndexToXY(int index, int offset)
{
	index = index * gDataSize + offset;
	return ivec2(index % int(uTDOutputInfo.res.z), floor(index / uTDOutputInfo.res.z));
}

// Helper function to retrieve a color of the texture input
vec4 Tex(int type, vec2 uv)
{
	return texture(sTD2DInputs[type], uv);
}

// Reads from output buffer. This will fetch the last frame that was rendered.
vec4 TexRead(int index, int offset)
{
	return imageLoad(sTDComputeOutputs[0], IndexToXY(index, offset));
}

// Writes a certain pixel of information to the output buffer
void TexWrite(int index, int offset, vec4 data)
{
	imageStore(sTDComputeOutputs[0], IndexToXY(index, offset), data);
}

// Reads the full particle struct and sets the global variable 
void Read(int index)
{
	vec4 life = TexRead(index, DATA_LIFE); // Reads the life data (index, lifetime, maxlife and state)

	gParticle.index = index;
	gParticle.lifetime = life.x;
	gParticle.maxlife = life.y;
	gParticle.state = int(life.z);

	vec4 position = TexRead(index, DATA_POSITION); // Position data xyz, size
	gParticle.position = position.xyz;
	gParticle.size = position.w;

	vec4 velocity = TexRead(index, DATA_VELOCITY);	// Velocity xyz, speed
	gParticle.direction = velocity.xyz;
	gParticle.speed = velocity.w;

	gParticle.color = TexRead(index, DATA_COLOR);	// Color rgba
}

// This functions creates a new particle. The function will be called when a particle is dead.
void Birth()
{
	vec2 xy = vec2(gParticle.index, uTime); // Creates a random seed per particle using the index and time

	gParticle.maxlife = mix(uParticleLife.x, uParticleLife.y, Hash(xy));	// Find a random life span
	gParticle.lifetime = gParticle.maxlife;	// Sets the current lifetime to the maximum life of this particle
	gParticle.state = PARTICLE_STATE_ALIVE;	// Reincarnate the particle

	{
		vec4 rnd = vec4(Hash(xy+1), Hash(xy+2), Hash(xy+3), Hash(xy+4));	// Adding an offset to make sure we can random numbers
		vec4 data = mix(uPositionSizeStart , uPositionSizeEnd, rnd);	// Find a random position and size
		gParticle.position = data.xyz;
		gParticle.size = data.w;
	}

	{
		vec4 rnd = vec4(Hash(xy+5), Hash(xy+6), Hash(xy+7), Hash(xy+8));
		vec4 data = mix(uDirectionSpeedStart, uDirectionSpeedEnd, rnd);	// Find a random velocity and speed
		gParticle.direction = normalize(data.xyz);
		gParticle.speed = data.w;
	}

	// Fetching the color of the particle. The uv position represents lifetime (x) and randomness (y)
	gParticle.color = Tex(TEX_COLOR_LIFERANDOM, vec2(0, Hash(vec2(gParticle.index))));
}

// Kill the particle
void Death()
{
	gParticle.state = PARTICLE_STATE_DEAD; 
}

// Add some gravity to the scene
void AddGravity()
{
	gParticle.direction = mix(gParticle.direction, vec3(0,-1,0), uGravity.x); // Updates the direction slightly downwards every frame
	gParticle.speed += max(0, dot(gParticle.direction, vec3(0,-1,0))) * uGravity.y * 0.01; // Add a bit of speed when pointing downwards 
}

// Adding some noise to the direction
void AddNoise()
{
	gParticle.direction += vec3(TDSimplexNoise(gParticle.position*uNoise.y), TDSimplexNoise(gParticle.position*uNoise.y + 1), TDSimplexNoise(gParticle.position*uNoise.y + 2))*uNoise.x;
}

// The main update function. This function updates the position, direction and lifetime.
void Update()
{
	if (gParticle.state == PARTICLE_STATE_ALIVE) {	// When it's alive
		AddGravity(); // Add some gravity
		AddNoise(); // Add some noise

		float life = 1-(gParticle.lifetime/gParticle.maxlife);	// Calculate the life fraction (0 to 1)

    // collision with floor
		if(gParticle.position.y <= uFloor){
			gParticle.position.y = uFloor + 0.1;
      float xPos = Hash(gParticle.position.xy) * 0.5 - 0.25;
      float yPos = Hash(gParticle.position.yz) * 0.7;
      float zPos = Hash(gParticle.position.zx) * 1 - 0.5;
      gParticle.direction += vec3(xPos,yPos,zPos);
		}
		// Update the position using the current direction and it's speed
		gParticle.position += normalize(gParticle.direction) * gParticle.speed * uSpeed;

		// circle collider
		float dist = distance(gParticle.position, uCollider);
    if(dist < 0.25){
    	float xPos2 = Hash(gParticle.position.xy) * .4 - .2;
      float yPos2 = Hash(gParticle.position.yz) * 0.2;
      // float zPos2 = Hash(gParticle.position.zx) * 2 - 1;
      float zPos2 = 0;
      gParticle.direction += vec3(xPos2,yPos2,zPos2);
      gParticle.speed *= 0.93;
    }
		
		

		gParticle.lifetime -= uFpsTick * uSpeed;	// Decrease it's current lifetime per frame
		gParticle.size = gParticle.size + uSizeOverLife * life * uSpeed; // Increase or decrease size over time

		// Fetch the new color (x according to the current life time fraction)
		gParticle.color = Tex(TEX_COLOR_LIFERANDOM, vec2(life, Hash(vec2(gParticle.index))));

		// Check we it's time to die
    	if (gParticle.lifetime < 0) {
    		gParticle.state = PARTICLE_STATE_DEAD;	// Sets the state of the particle to dead. So the next time it will reincarnate
    	}
	} else if (gParticle.state == PARTICLE_STATE_DEAD) { // When it's dead
   		Birth(); // Give birth to a new particle
    }
}

// Writes the current global particle struct to the output buffer
void Write()
{
	TexWrite(gParticle.index, DATA_LIFE, vec4(gParticle.lifetime, gParticle.maxlife, gParticle.state, 0));
	TexWrite(gParticle.index, DATA_POSITION, vec4(gParticle.position, gParticle.size));
	TexWrite(gParticle.index, DATA_VELOCITY, vec4(gParticle.direction, gParticle.speed));
	TexWrite(gParticle.index, DATA_COLOR, gParticle.color);
}

void main()
{
	// Calculate the current index. (x + y * maximum width)
	int index = int(gl_GlobalInvocationID.x + gl_GlobalInvocationID.y * gl_NumWorkGroups.x * gl_WorkGroupSize.x);

	if (uReset > 0) { // Reset the output buffer
		imageStore(sTDComputeOutputs[0], ivec2(0), vec4(0));	
		for (int i = 0; i < gDataSize; i++) { // Make sure all vec4's are set to 0
			imageStore(sTDComputeOutputs[0], IndexToXY(index, i), vec4(0));	
		}
		return;
	} else if (index < uParticles) { // Make sure we don't exceed our maximum amount of particles
    	Read(index); // First read the particle from the last output buffer
   		Update(); // Then update it's position and direction
    	Write(); // And write it back to the output buffer
    }
}