SER431 Lecture 12

Advanced Graphics
Particle Systems
(201809)

Transcript

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   SER 431
   Advanced Graphics
   Lecture 12: Introduction to Particle Systems
   Javier Gonzalez-Sanchez
   javiergs@asu.edu
   PERALTA 230U
   Office Hours: By appointment
   

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2. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 1
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   Particle Systems
   § Uses a large number of very small graphic objects to simulate "fuzzy"
   phenomena
   § Examples: fire, explosions, smoke, moving water (such as a waterfall),
   sparks, falling leaves, rock falls, clouds, fog, snow, dust, meteor tails, stars
   and galaxies
   

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3. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 2
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   Implementation
   § Emitter: a source of particles
   § Particles behavioral parameters
   a) spawning rate: how many particles are generated per unit of time
   b) initial velocity vector: the direction they are emitted upon creation
   c) lifetime: the length of time each individual particle exists before
   disappearing
   a) color
   b) etc.
   § Most parameters are "fuzzy" — instead of a precise numeric value, it is
   specified a central value and the degree of randomness allowable on
   either side of the central value.
   

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4. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 3
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   Example
   Images from:
   http://www.gamefromscratch.com/post/2015/07/09/Godot-Engine-Tutorial-Part-12-Particles.aspx
   

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5. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 4
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   Source Code
   

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6. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 5
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   Particle
   class Particle {
   public:
   float position[3];
   float direction[3];
   float life;
   Particle * next;
   Particle() {
   position[0] = 0.5f;
   position[2] = 0.5f;
   position[1] = 0.0f; // emitter location
   direction[0] = (10000 - rand() % 20000) / 10000.0f;
   direction[1] = (10000 - rand() % 20000) / 10000.0f;
   direction[2] = (10000 - rand() % 20000) / 10000.0f; // -1 to 1 ?
   life = rand() % 10000 / 10000.0f; // 0 to 1
   }
   };
   

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7. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 6
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   Particle System
   class ParticleSystem {
   public:
   Particle * particle_head;
   void add();
   void update(float time);
   void remove();
   };
   

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8. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 7
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   Particle System | add
   // add
   void add() {
   Particle* p = new Particle();
   p->next = particle_head;
   particle_head = p;
   }
   

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9. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 8
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   Particle System | update
   // update
   void update(float time) {
   Particle* p = particle_head;
   while (p) {
   p->life -= time; // decrease lifespan
   p->direction[1] += 9.81f * time; // why?
   // modify position
   p->position[0] += time * p->direction[0];
   p->position[1] += time * p->direction[1];
   p->position[2] += time * p->direction[2];
   p = p->next;
   }
   }
   

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10. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 9
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    Particle System | remove
    void remove() {
    Particle* curr = particle_head;
    Particle* prev = 0;
    while (curr) {
    if (curr->life < 0) {
    if (prev) prev->next = curr->next;
    else particle_head = curr->next;
    Particle* temp = curr;
    curr = curr->next;
    delete temp;
    } else {
    prev = curr;
    curr = curr->next;
    }
    }
    }
    

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11. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 10
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    Particle System | display 1
    ParticleSystem ps;
    void display() {
    // known code here ...
    ps.add();
    ps.update(0.001);
    ps.remove();
    glPushMatrix();
    drawParticles();
    glPopMatrix();
    // known code here...
    }
    

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12. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 11
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    Particle System | display 2
    ParticleSystem ps;
    void init() {
    init_frame_timer();
    // known code here ...
    }
    void display() {
    // old code here ...
    ps.add();
    ps.update(calculate_frame_time());
    ps.remove();
    glPushMatrix();
    drawParticles();
    glPopMatrix();
    // known code here...
    }
    

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13. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 12
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    Particle System | frame time
    void init_frame_timer() {
    LONGLONG rate;
    // Counts per second: 2,435,913
    if (!QueryPerformanceFrequency((LARGE_INTEGER*)&rate)) return;
    if (!rate) return;
    // Improved value if nothing fail (returned)
    frequency = 1.0f / (float)rate;
    // Time stamp (performance-counter value): 27 929 379 692
    if (!QueryPerformanceCounter((LARGE_INTEGER*)&start_clock))
    return;
    }
    

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14. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 13
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    Particle System | frame time
    float get_current_time() {
    LONGLONG end_clock;
    QueryPerformanceCounter((LARGE_INTEGER*)&end_clock);
    return (end_clock - start_clock) * frequency;
    }
    

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15. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 14
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    Particle System | frame time
    float calculate_frame_time() {
    do {
    endOfFrame = get_current_time();
    } while (endOfFrame == startOfFrame);
    float f = endOfFrame - startOfFrame;
    ++dx;dx = dx % 5;
    lastFiveTimes[dx] = f;
    startOfFrame = endOfFrame;
    float *p = lastFiveTimes;
    float *e = p + 5;
    averageFrameTime = 0.0f;
    for (; p != e; ++p) { averageFrameTime += *p;}
    averageFrameTime *= 0.2f;
    return averageFrameTime;
    }
    

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    Test Yourselves
    

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17. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 16
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    Test
    

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18. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 17
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    Bonus
    

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    Bonus Points
    Due date: Saturday, September 29, 11:59 PM
    

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20. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 19
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    Bonus
    Point to be added to your final grade:
    a) +1 for a simple implementation of fire changing particles color
    and/or size and emulating smoke and flames. Such as in the
    image here
    b) +3 for a realistic implementation of fire. Something similar the
    image here : colors, blending (transparency), improved
    physics, lighting.
    c) +5 for a WoW implementation. Additional programming is
    needed. Something equal or better than the image here
    * In all cases we are talking about a fire in 3D – it is not flat.
    

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21. jgs
    SER431 Advanced Graphics
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Fall 2018
    Disclaimer. These slides can only be used as study material for the class SER431 at ASU. They cannot be
    distributed or used for another purpose.
    

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