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).

History

• First release.

This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)