Assignment 5: Special effects

Due Thursday, April 29, before midnight

The goals for this assignment are:

  • Implement particle systems using point sprites, or billboards

1. Getting started

Fork the repository at https://github.com/BrynMawr-CS312-2021/particles

Follow the instructions in Readme.md to build and run the code.

2. Getting started

You are given basecode for rendering quads with textures. The basecode uses

3. Billboards

Edit the shader billboard.vs to draw a billboard. Your billboard should be

  • centered at the position uOffset

  • scaled to match uSize

  • rotated to point towards uCameraPos

To get started, run the program implemented in main-billboard.cpp. This program uses the class Renderer to draw a single billboard using the shader billboard.vs and billboard.fs.

On windows

build $ ../bin/Debug/billboard.exe

and on mac

build $ ../bin/billboard

When you run this program, you should see

billboard start

This program implements a billboard as a quad with vertices at (0,0,0), (1,0,0), (1,1,0), and (0,1,0). It textures the quad using the image particle.png.

After you implement the position and scale (do not multiply by uVP yet), you should see

billboard scale offset

Next, apply the view-projection matrix to the billboard position. You should see

billboard norot

The camera is rotating around the billboard, but the image does not remain facing the camera. Compute and apply a rotation matrix in your shader that points the billboard towards the camera (Hint: use cross products). Once working, you should see

billboard rot

4. Confetti

In confetti.cpp, implement a particle system with the following features

  • The initial position of each particle is randomly within a unit cube

    • Hint: use the function random_unit_cube defined in AGLM.h

  • The colors of each particle is randomized

  • The velocities of each particle is randomized

  • The size of each particle is 0.25

  • The particles should stay within a cube with minimum point (-1,-1,-1) and maximum point (1,1,1)

On windows

build $ ../bin/Debug/confetti.exe

and on mac

build $ ../bin/confetti

Walkthrough and hints:

  • The particle system, Confetti, overrides the abstract class ParticleSystem, defined in particlesystem.h. Subclasses must override createParticles and update. The base class contains the renderer and performs drawing each frame.

  • The main application is implemented in main-confetti.cpp

  • In the function Confetti::createParticles,

    • load the particle texture with the code mTexture = theRenderer.loadTexture("../textures/particle.png");

    • initialize the list of particles based on the size. The baseclass manages its list of particles using std::vector mParticles. Use the function push_back to add particles to mParticles

  • In the function Confetti::update, update the position of each particle based on its velocity.

    • If the position goes out of the bounds [-1,1], reflect the velocity

At this point, you should see the following with a single particle (edit confetti-main.cpp to initialize the system to have 1 particle).

confetti single

With 500 particles, you should see

Notice all the black, square edges. This occurs because our particles are not drawn from back to front in relationship to the camera. The blending cannot work correctly if the particles are not sorted. To fix this, you should also sort the particles in update.

  • You can call theRenderer.cameraPosition() to get the camera position.

  • You can use a sorting shortcut which takes advantage of the fact that particles do not shift too much between frames (called spatial and temporal coherency). In this approach, go through the list once, compare consecutive particles, and swap if one particle should be in front of another.

// cheap sort
for each particle
   d2 = distance from particle to camera
   d1 = distance from previous particle to camera
   if d2 < d1
      swap(particle, previous particle)

5. Unique demo

Implement a unique particle system. Here are some ideas:

  • Fire (animated sprites)

  • Smoke plume

  • Fireworks

  • Sparkle trailing effect

  • Implement your particle system as a subclass of ParticleSystem in myparticlesystem.h/cpp

  • Test your particle system in main-demo.cpp

On windows

build $ ../bin/Debug/demo.exe

and on mac

build $ ../bin/demo

6. Update Readme.md

Update Readme.md to include documentation on your unique features and images created with your mesh-viewer.

7. What to hand in

  1. Your code. Make sure your code is checked into github

  2. One or more images created using your software

  3. Update Readme.md so it includes a writeup of the features your application supports. Make sure to include images. Be sure to point out any original features that you implement.