Hello, is anyone out there?… I haven’t posted anything for quite sometime now. Hopefully all that will change as i get more free time to organize and work on my projects. Meanwhile, i would like you to know about something else..

Look down, you should be looking at a bar, a dark bar with a few buttons on the right side. I’ve been thinking about this for sometime but as my webdev skills/will are at the same level (low) i was looking to some ready-to-use code. I did. You can find it here and at my portfolio, my two windows to the world. Thanks to this guys here (for the ugly code rip) and Filipe ‘ps’ Cruz for help with css.

On this case we will need 4 points: 2 anchor points (the line end points) and 2 control points. The control points won’t really touch the curve, they work more as directional information on the curve itself.

As we need to send this data to the shader i have decided to use  LINES as input primitive, 2 points define a line so it’s perfect, we’ll use that for the 2 anchor points. As for the control points 2 different texture units (glMultiTexCoord3f) attached to the line’s vertex data will do. Using geometry shaders besides setting the input primitive type we also need to set the output type. LINE_STRIP is fine, as it works perfectly for what we’re doing. That’s all on the application side.

On the vertex shader side it’s pretty simple:

[VERTEX SHADER]
void main( void )
{
    gl_FrontColor = gl_Color;
    ControlPoint1 = gl_MultiTexCoord0.xyz;
    ControlPoint2 = gl_MultiTexCoord1.xyz;
 
    gl_Position = gl_Vertex;
}

What the code is doing is sending the data further down the pipeline to the geometry shader, where all the magic happens. At this stage, having both Anchor and Control points we can now define the curve by a given detail. Think of detail as a number of step-points along the curve which makes it look smoother or flatten (tesselation, subdivision, smoothing, etc).

Both control points are sent by the application for the geometry shader, still, as in the the vertex shader comes before the geometry shader, we will need to send them down on the vertex-shader, otherwise the GS won’t be able to “see” them (i know, hurray for Cg). We’re now almost done. By using the function from the above link(s) and as shown below we compute the curve with a given detail on the geometry shader, by generating new vertices along the curve purely on the gpu side. I think it to be pretty straightforward and the code should be self-explanatory.

[GEOMETRY SHADER]
uniform int g_Detail;
varying in vec3 ControlPoint1[];
varying in vec3 ControlPoint2[];
 
// Found in nvidia sdk
vec3 evaluateBezierPosition( vec3 v[4], float t )
{
    vec3 p;
    float OneMinusT = 1.0 - t;
    float b0 = OneMinusT*OneMinusT*OneMinusT;
    float b1 = 3.0*t*OneMinusT*OneMinusT;
    float b2 = 3.0*t*t*OneMinusT;
    float b3 = t*t*t;
    return b0*v[0] + b1*v[1] + b2*v[2] + b3*v[3];
}
 
void main()
{
    vec3 pos[4];
    pos[0] = gl_PositionIn[0].xyz;
    pos[1] = ControlPoint1[0];
    pos[2] = ControlPoint2[0];
    pos[3] = gl_PositionIn[1].xyz;
    float OneOverDetail = 1.0 / float(g_Detail-1.0);
    for( int i=0; i<g_Detail; i++ )
    {
        float t = i * OneOverDetail;
        vec3 p = evaluateBezierPosition( pos, t );
        gl_FrontColor = gl_FrontColorIn[0]; 
        gl_Position = gl_ModelViewProjectionMatrix * vec4( p.xyz, 1.0 );
        EmitVertex();
    }
 
    EndPrimitive();
}

What’s next? That is up to you. You’re not going to leave me with all the work, are you ?

Download the example + source.
You will also need to install Vitamin 0.5.6 as the project is built with it.

There is no executable this time, as i don’t know if i can spread the music, still, nobody can stop me  (for the moment) from giving you a video. So here it is, Float.

Next step was to optimize the cube generation by lowering from a 24 vertex cube to 14 vertex triangle strip. Things got better, but nothing close to my expectations. I was not satisfied, i mean, i had alot of cubes on screen (100K which was not that much) and that was it, nothing else. We’re talking about 20fps or so, for 100.000 cubes (around 1.2 million triangles per frame). Later on i added vertex normals to the geometry shader and started to work on some lighting/shadowing, but i ended up going back on the rendering side of the job. Meanwhile, i was speaking with a friend of mine about this idea and we were discussing ways to compute lighting but i couldn’t stop thinking about my real problem. So it came to me.

Previously, i have done some experiments with opengl hardware instancing, but never got  to do much about it .  What better time than now, so i grabbed the project and took it for a spin. After a few hours i had the same amount of cubes on screen with a much much better framerate. Quickly implemented some eye-candy (coloring, texturing, vertex lighting), some tweaking here and there and as i was listening to Mr. Peter Broderick (hi, i love you man) added some audio analysis to the feature list.
Last but not least, a kind of “Brownian Motion” was used to generate points in space, increased the cube count to 512*512 and watched it flow ( at 20fps ).

In conclusion, Hardware instancing was much easier to implement  and performance seems much better at first sight. Above is a video of 262.144 audio-reactive cubes with GPU animation and basic lighting at around 20fps. For my video card i think that is very good. On a sidenote, i have not given up on the geometry shaders. I am not sure what will be my next step regarding the subject (back to geometry shaders?) but for now this is it. Hardware Instancing kicked Geometry Shaders in the ass.

“Function2Form is a work on form and shape generation from the subdivision of space and image analysis. It has no rules other than the creation/deformation of limited space. It’s a study on photography. It’s a random case of geometry generation and a study of differences for different parameters and areas. Based on randomness i would say these are unique and lost generated pieces of a kind.“

Created with a custom framework for scene generation and 3dsmax for the rendering.

Note: For the complete series, check out The Viewer #5

For more information about the project, look further down the spiral: Official Release | Source code released

To achieve this i’ve picked Vertex Texture Fetch. It allows you to access texture data on the vertex shader. Pass a texture to the vertex shader and offset the surface vertices by the pixel’s intensity. To improve the looks, bump-mapping with multiple lights have been used. Everything presented here is generated on the GPU, even the objects. Runs nicely on a Nvidia 8200M. Lots of  space for improvement.

]]> http://www.pixelnerve.com/v/2009/11/04/hmm-greebles/feed/ 0 http://www.pixelnerve.com/v/2009/10/30/opencl-4-java/ http://www.pixelnerve.com/v/2009/10/30/opencl-4-java/#comments Fri, 30 Oct 2009 18:09:42 +0000 victormartins http://www.pixelnerve.com/v/?p=834 I finally took  the time to play with OpenCL. I was motivated by the particle example from Rui Madeira. After speaking with him, he gave me a few other links on more examples like Memo Akten‘s 1.000.000 particles running with mouse interaction on the GPU, the very NVidia’s first OpenCL application example, etc. I was intriged!  So i took the day to play with OpenCL4Java and ported Rui’s example to Java running on Processing’s IDE.  I’ve tested it with a Intel Quad core and i found the Rui’s sample to crash with GTX280 videocard. I didn’t gave it much thought but it might be for that for-loop in the program on the particle-particle iteration. In the other hand, Memo’s example ran easily on the gpu side. I should have made an example of mine, but it was easier to just port their examples and get things running. That was the main goal.

I have only tested this under Windows XP 64bit with ATI Stream SDK and Nvidia drivers. If you find any problem, please report.
One other thing: Memo’s example isn’t the real thing. It’s simply the CL program. So you won’t be able to get all the fuzzy million particles around. Not yet.

Library/Examples available here: http://victamin.googlecode.com/files/OpenCL4Java_1b.zip

Installation steps:
1. Copy the library to processing’s libraries folder
2. Install ATI Stream SDK (i have packed the OpenCL.dll file, still you might have to install the whole pack). If you’re using Nvidia, install the OpenCL drivers and toolkit
3. Open the example and run it.

Enjoy and have fun!

Download from scene.org