A Lightweight Real-time OpenGL Graph Component

Download demo project with source - 82.4 Kb

Introduction

I had this need to show some statistics through a graph in real-time, in a demo application which I wrote. The screenshot should illustrate clearly the idea behind this graph component. It will be useful for programmers who would like to track data in real-time, such as in data acquisition and analysis. I did not have time to develop something really elaborate, like different graph types, presentation options, and filters, but it should be very easy to add-on these functionalities from the code.

Using the code

Some of the features of this graph component are:

A user-defined cache (list) for storing the graph data
When data "overflows" the cache, the graph automatically discards the oldest data to create space for the latest data
Moving average is calculated on-the-fly

It is very easy to include this code into any OpenGL-based application. The programmer only needs to make sure he/she has the rendering context.

OGLGraph* myGraph;

void init ( GLvoid )     // Create Some Everyday Functions
{
    glClearColor(0.0f, 0.0f, 0.0f, 0.f);
    //glClearDepth(1.0f);            
    myGraph = OGLGraph::Instance();
    myGraph->setup( 500 /*width*/, 100 /*height*/, 
                    10 /*offsetX*/, 10 /*offsetY*/, 
                    2 /*scaleX*/, 2 /*scaleY*/, 
                    1 /*channels*/, 200 /*cache size*/ );
}

void display ( void )   // Create The Display Function
{
    // ... 

    // This is a dummy function. Replace with custom input/data
    float time = glutGet(GLUT_ELAPSED_TIME) / 1000.0;
    float value;
    value = 5*sin( 5*time ) + 10.f;

    myGraph->update( value );
    myGraph->draw();
}

Source code builds nicely in MS VS.NET 2003.

Points of Interest

You can include any filters like noise reduction, low-pass, or high-pass in the update() code, or even pass post-processed data into this function if you can do that with an external software (e.g., using Matlab).