Sign in to follow this  

OpenGL Billboarding particle system in vertex shader

This topic is 1602 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I've been working on a GPU driven particle system for mobile devices (OpenGL ES 2.0). I've gotten stuck on one part of it, namely billboarding the particles in the vertex shader. Since there is no vertex texture fetch in OpenGL ES 2.0 I have packed all the data each particle needs into the vertex buffer, this somewhat limits the effects I can achieve with the system, but it's good enough for what I need.


The problem is that after the position, etc. for each particle has been calculated, it's no longer positioned at the origin in the local space of the particle system, so when I apply my billboarding the entire particle system gets billboarded as one unit - but this is obviously not what I want as I want to billboard each particle individually. And I simply can not come up with a way to do this inside the vertex shader.

Share this post

Link to post
Share on other sites

I just billboard particles at view space.


1. Simulation calculate particle world space position.

2. Transform position to view space.

3. Expand particle using texture coords.(if uv are range of [0 : 1] corner is located at: viewSpacePosition - (uv - 0.5) * size) Optionally rotated around view space z.

Share this post

Link to post
Share on other sites

kalle_h: if I'm not mistaken, this solution requires you to do some of the work on the CPU right? I have quite a lot of particles, and i'm doing this on a mobile device (iPhone 3GS), I have literally 0 CPU budget for this.

Share this post

Link to post
Share on other sites

kalle_h: if I'm not mistaken, this solution requires you to do some of the work on the CPU right? I have quite a lot of particles, and i'm doing this on a mobile device (iPhone 3GS), I have literally 0 CPU budget for this.

0% cpu work.


Code snippet from actual shader code. This requires particles to have angle and world space position from some where.(I get those from stateless vertex shader simulation).

highp vec4  pos      = u_viewMatrix * vec4(position, 1.0);
highp float sinA     = sin(angle);
highp float cosA     = cos(angle);
highp vec2 posOffset = size * (texcoord - vec2(0.5));

pos.xy += vec2(cosA*posOffset.x + sinA*posOffset.y, -cosA*posOffset.y + sinA*posOffset.x);

gl_Position = u_projectionMatrix * pos;

Share this post

Link to post
Share on other sites

kalle_h: Thanks for all your help, the solution I ended up with is a bit different, because for some reason I couldn't get your example to work (I'm with  you on the world position, but not sure where you derive the angle from). Anyway, my solution works like this:


1) I generate a mesh dynamically which contains all my particle quads, the data is packed like this into the vertex buffer:

POSITION: Midpoint of the quad

TEXCOORD0: Offset of this vertex from the midpoint
2) In the vertex shader I do the following operations:

First, I apply my particle simulation, which gives me the middle point of the current quad in local space of the particle system

Second, I transform the quad to view space

Third, I apply the offset of the quad on the X/Y axes of the mid point

Fourth, I transform the resulting vertex with the Projection matrix


The exact shader code I use looks like this:


                VEC4 viewSpace = mul(ModelView, VEC4(localSpace, 1));
                viewSpace.x += i.uv.x;
                viewSpace.y += i.uv.y;
                o.pos = mul(Projection, viewSpace);


This seems to be working fine, but is there any drawback to doing it like this in viewspace?

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Similar Content

    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
    • By dpadam450
      I have this code below in both my vertex and fragment shader, however when I request glGetUniformLocation("Lights[0].diffuse") or "Lights[0].attenuation", it returns -1. It will only give me a valid uniform location if I actually use the diffuse/attenuation variables in the VERTEX shader. Because I use position in the vertex shader, it always returns a valid uniform location. I've read that I can share uniforms across both vertex and fragment, but I'm confused what this is even compiling to if this is the case.
      #define NUM_LIGHTS 2
      struct Light
          vec3 position;
          vec3 diffuse;
          float attenuation;
      uniform Light Lights[NUM_LIGHTS];
    • By pr033r
      I have a Bachelor project on topic "Implenet 3D Boid's algorithm in OpenGL". All OpenGL issues works fine for me, all rendering etc. But when I started implement the boid's algorithm it was getting worse and worse. I read article ( inspirate from another code (here: but it still doesn't work like in tutorials and videos. For example the main problem: when I apply Cohesion (one of three main laws of boids) it makes some "cycling knot". Second, when some flock touch to another it scary change the coordination or respawn in origin (x: 0, y:0. z:0). Just some streng things. 
      I followed many tutorials, change a try everything but it isn't so smooth, without lags like in another videos. I really need your help. 
      My code (optimalizing branch):
      Exe file (if you want to look) and models folder (for those who will download the sources):
      Thanks for any help...

    • By Andrija
      I am currently trying to implement shadow mapping into my project , but although i can render my depth map to the screen and it looks okay , when i sample it with shadowCoords there is no shadow.
      Here is my light space matrix calculation
      mat4x4 lightViewMatrix; vec3 sun_pos = {SUN_OFFSET * the_sun->direction[0], SUN_OFFSET * the_sun->direction[1], SUN_OFFSET * the_sun->direction[2]}; mat4x4_look_at(lightViewMatrix,sun_pos,player->pos,up); mat4x4_mul(lightSpaceMatrix,lightProjMatrix,lightViewMatrix); I will tweak the values for the size and frustum of the shadow map, but for now i just want to draw shadows around the player position
      the_sun->direction is a normalized vector so i multiply it by a constant to get the position.
      player->pos is the camera position in world space
      the light projection matrix is calculated like this:
      mat4x4_ortho(lightProjMatrix,-SHADOW_FAR,SHADOW_FAR,-SHADOW_FAR,SHADOW_FAR,NEAR,SHADOW_FAR); Shadow vertex shader:
      uniform mat4 light_space_matrix; void main() { gl_Position = light_space_matrix * transfMatrix * vec4(position, 1.0f); } Shadow fragment shader:
      out float fragDepth; void main() { fragDepth = gl_FragCoord.z; } I am using deferred rendering so i have all my world positions in the g_positions buffer
      My shadow calculation in the deferred fragment shader:
      float get_shadow_fac(vec4 light_space_pos) { vec3 shadow_coords = / light_space_pos.w; shadow_coords = shadow_coords * 0.5 + 0.5; float closest_depth = texture(shadow_map, shadow_coords.xy).r; float current_depth = shadow_coords.z; float shadow_fac = 1.0; if(closest_depth < current_depth) shadow_fac = 0.5; return shadow_fac; } I call the function like this:
      get_shadow_fac(light_space_matrix * vec4(position,1.0)); Where position is the value i got from sampling the g_position buffer
      Here is my depth texture (i know it will produce low quality shadows but i just want to get it working for now):
      sorry because of the compression , the black smudges are trees ...
      EDIT: Depth texture attachment:
  • Popular Now