Back to posts.

# Bouncing particle effect

A snippet which shows how to create a particle system which keep bouncing around a certain point. You can control the forces easily by settings the `repel_force` and `attract_force`.

Normally when you create a basic, simple particle system using plain Euler integration you can use something like the snippet below to make sure the velocity gets less over time (aka fake drag).

`particle.velocity *= 0.99f;`

Though, when you use this it's hard to make your particles bounce forever. To fix this, you remove the fake drag but simply limit the velocity to a certain value, see `max_speed` in the code.

In short the integration step is:

```// ATTRACT FORCES
float max_speed = 4;
float max_speed_sq = max_speed * max_speed;
float speed_sq;
float k = 1.0f;

for(size_t i = 0; i < drops.size(); ++i) {
WaterDrop& d = drops[i];

{
dir = position - d.position;
dist = length(dir);

if(dist < 0.01) {
dist = 0.01;
}

if(dist > radius) {  /* when the particle is outiside the radius, it's attracted a lot more to the center */
k = 16.0;
}

dir /= dist;
f = k * attract_force * (dist/radius) * dir;
d.forces += f;
}

d.forces *= d.inv_mass * dt;
d.velocity += d.forces * dt;
d.position += d.velocity;
d.forces = 0;

// we do not add a fake drag force, but we limit the speed, this will make the
// particles bounce forever.
speed_sq = dot(d.velocity, d.velocity);
if(speed_sq > max_speed_sq) {
d.velocity = normalized(d.velocity);
d.velocity *= max_speed;
}
}```

We also add a repel force so the particle do not get to close and more importantly to make the particles jump a little bit. I needed this effect for a visualisation I'm working on.

```for(size_t i = 0; i < drops.size(); ++i) {

WaterDrop& a = drops[i];

for(size_t j = i + i; j < drops.size(); ++j) {

WaterDrop& b = drops[j];
dir = b.position - a.position;
dist_sq = dot(dir, dir);

if(dist_sq > neighbor_dist_sq) {
continue;
}

if(dist_sq < 0.01) {
continue;
}

dir = normalized(dir);
f = repel_force *  (1.0 - (1.0 / dist_sq)) * dir;
a.forces -= f;
b.forces += f;
}
}```

See a video of this effect

• NAT Types This is so exciting, in this article I dive into some of the different ways a NAT device translates addresses which is important for peer-to-peer connections.
• Building Cabinets In this post I dive into the design and construction of a cabinet with an interact LED strip. I also explain how I dynamically change the colors of the LEDs over TCP/UDP.
• Compiling GStreamer from source on Windows How to compile GStreamer on Windows from Source using Visual Studio 2019 and the meson build system.
• Debugging CMake Issues In this post I explain a process you can follow to debug issues with CMake by focusing on a specific target and making the output verbose.
• Dual Boot Arch Linux and Windows 10 How to install Arch Linux and Windows 10 Pro as dual boot. A step by step tutorial how to create bootable installers, partition and setup a dual boot menu.
• Mindset Updated Edition, Carol S. Dweck (Book Notes) Paragraphs I marked from the book "Mindset" from Carol S. Dweck.
• How to setup a self-hosted Unifi NVR with Arch Linux A step by step HOW-TO that explain show to setup a Unifi Video Controller with an NFS share with Arch Linux.
• Blender 2.8 How to use Transparent Textures Follow this node setup when you want to use an image with transparency as a "sticker".
• Compiling FFmpeg with X264 on Windows 10 using MSVC A couple of steps to compile FFmpeg on Windows using MSVC.
• Blender 2.8 OpenGL Buffer Exporter The following Blender script creates a [name].h and [name].cpp for the selected object and stores the positions, normals and UVs.
• Blender 2.8 Baking lightmaps Light maps are a cheap way to add a lot of realism to you static scenes and have been used forever.
• Blender 2.8 Tips and Tricks Use Environment Map only for reflections; create a floor plane for a Product Render, diffuse texture for roughness and more!
• Setting up a Bluetooth Headset on Arch Linux Learn how to setup a Sennheiser PXC 550 Bluetooth headset on Arch Linux.
• Compiling x264 on Windows with MSVC Compile the excellent x264 source on Windows using MSYS2 and MSVC.
• C/C++ Snippets Is a number divisible by four?
• Reading Chunks from a Buffer Some thoughts on reading bytes from a file; handy for reading NALs.
• Handy Bash Commands Bash scripts: removing white space, lowercase filenames, backup using tar, etc.
• Building a zero copy parser Simple solution to parse data in a pretty performant way. Used this for a RTSP protocol parser.
• Kalman Filter A very simple yet powerful filter which works great when you have to smooth noisy data. Used for the Nike Rise 2.0 project.
• Saving pixel data using libpng Do you have raw RGBA data that you want to save? Use this snippet to save it into a PNG file.
• Compile Apache, PHP and MySQL on Mac 10.10 Setup you own PHP, MySQL and Apache and with virtual document roots.
• Fast Pixel Transfers with Pixel Buffer Objects Using Pixel Buffer Objects (PBO) for fast asynchronous data transfers and OpenGL.
• High Resolution Timer function in C/C++ Wait...... wait.. fast high resolution timer funtions (Windows, Linux, Mac)
• Rendering text with Pango, Cairo and Freetype My never ending obsession with font rendering. A complex beast to do well. Use Pango and FreeType for the heavy lifting.
• Fast OpenGL blur shader Make things look blurry ... and fast using this OpenGL blur shader.
• Spherical Environment Mapping with OpenGL An old trick to get great lighting effects using Environment Maps and OpenGL.
• Using OpenSSL with memory BIOs OpenSSL is a great library with lots of abstractions. In this post I discuss how to break some of these abstractions and use your own memory buffers.
• Attributeless Vertex Shader with OpenGL A simple way to render a fullscreen quad without a vertex buffer with OpenGL.
• Circular Image Selector Some thoughts on a different way to select images from a huge collection in a compact UI.
• Decoding H264 and YUV420P playback Using libav to demux and playback with OpenGL.
• Fast Fourier Transform Analyse your audio using the Fastest Fourier Transform in the West.
• OpenGL Rim Shader Pretty glowy edges using a GLSL rim shader.
• Rendering The Depth Buffer Render the non-linear OpenGL Depth Buffer.
• Delaunay Triangulation Do you need to triangulate some shape: use the “Triangle” library.
• RapidXML RapidXML is a versatile and fast XML parser with a simple API. Check out these examples.
• Git Snippets Some simple GIT snippets; added here to remind myself.
• Basic Shading With OpenGL A couple of basic GLSL shaders with explanation.
• Open Source Libraries For Creative Coding Collection of great open source libraries for you creative programming projects.
• Bouncing particle effect Snippet that can be used to create a bouncy particle effect; basic, effective, simple but nice.
• OpenGL Instanced Rendering Want to render thousands and thousands of objects? Use OpenGL instanced rendering. The solution...the only solution.
• Mapping a texture on a disc Ever heard about projective interpolation related to texture mapping? Learn about this intertesting issue with OpenGL and texture mapping.
• Download HTML page using CURL When you want a quick solution to perform a HTTP(S) request CURL is always a quick an simple solution. Check out this example code.
• Height Field Simulation on GPU Although not a Navier-Stokes implementation ... still a very nice and enjoyable effect.
• OpenCV Optical Flow: when doing anything with tracking you've probably heard of it. See this simple example code using OpenCV and OpenGL.
• Some notes on OpenGL FBOs and Depth Testing, using different Attachment Points, a YUV420p shader, ...
• Math Meaning of the Dot Product in 3D graphics, calculating a perpendicular vector using Sam Hocevar's solution, orientation matrix and more.
• Gists to remember Some gists that I want to remember, often use, etc...
• Reverse SSH Do you want to login, into a remote PC but the remote PC is behind a firewall? Then use this simple reverse SSH trick which doesn't require changing your firewall rules.
• Working Set Having issues with your compiler? Or during linking? Check these common issues and their solutions. I also list several tools that you can use to get a some useful info.
• Consumer + Producer model with libuv Example of a common Multi Threaded Consumer/Producer Model using LibUV.
• Parsing binary data Learn about the basic of a binary protocol and how to create one easily yourself.
• C++ file operation snippets Reading a file into a string, vector, checking the file size, change to a position, etc. A collection of C++ file operation snippets.
• Importance of blur with image gradients Do you want to experiment with OpenGL and aligning Brush Strokes along Image Gradients? Then check out this post about the importance of blurring.
• Real-time oil painting with openGL Code snippet for fake "oil painting" effect with OpenGL using instanced rendering.
• x264 encoder Basic example on how to use libx264 to encode image data using libav
• Generative helix with openGL Screenshots of a project I worked on with that generates a DNA helix.
• Mini test with vector field Screenshots while experimenting with a vector field; nothing much to see here.
• Protractor gesture recognizer Testing the amazing One Dollar \$1 gesture recognizer. The simplest and very good gesture recognizer.
• Hair simulation Example code that implements the "Fast Simulation of Inextensible Hair and Fur" paper from M. Müller, T.Y. Kim and N.Chentanez.
• Some glitch screenshots Glitch screenshots.
• Working on video installation Screenshots of some experiments of a video installation.
• Generative meshes I enjoy creating physics based simulations and render them on high res. Here are some experiments I did a time ago.
• Converting video/audio using avconv Examples that show you how to use avconv to manipulate video and audio files.
• Auto start terminal app on mac Automatically start you application whe Mac boots and make sure that it restarts your app when it exists. Handy for interactive installations.
• Export blender object to simple file format Export the selected object in Blender into a .h and .cpp file that prepresents the buffer.