This ofxAddon is basically a wrapper/adaptation of Jonathan de Halleux's contour-plotting c++ code (A C++ implementation of an improved contour plotting algorithm) which is based on Michael Joseph Aramini's thesis Implementation of an improved Contour Plotting Algorithm.
The first example demonstrates contour-plotting of mathematical functions f(x,y). On the left is a pixel drawing of the function, on the right the contour-plot based on the same function.
In the header file you need to instantiate a CContour object and two callback functions. One callback functions lets the CContour object sample what you want to draw, and the other one lets you draw the generated contour plot. Both callback functions are defined as static functions of ofApp.
class ofApp : public ofBaseApp{
CContour contour;
static double fieldFunction(ofApp * parent, double x, double y);
static void drawPlot(ofApp * parent, int iPlane,int x1, int y1, int x2, int y2);
};Now define the callback function that feeds the contour plot algorithm. Default input range from CContour for x|y is 0 to 5. Instead of handing back a value based on a mathemtical algorithm, you could also hand back the brightness of a pixel at x|y of an image.
double ofApp::fieldFunction(ofApp * parent, double x, double y) {
// if you want to refer back to objects/variables in the
// the main ofApp do it like this:
// parent->inputGridSize
return sin(x*2) + cos(y*2);
}Define the callback function that lets you draw the contour plot. In every call CContour will hand you back individual lines (x1, y1, x2, y2) and the number of the contour plane (iPlane).
void ofApp::drawPlot(ofApp * parent, int iPlane,int x1, int y1, int x2, int y2) {
ofSetColor( ofMap(iPlane, 0, parent->contour.GetNPlanes(), 0, 255) );
ofLine(x1,y1,x2,y2);
}In setup() you need to register the two callback functions and can define parameters for the contour plot.
void ofApp::setup(){
// register callback functions
contour.SetFieldFcn(fieldFunction, this);
contour.SetDrawFcn(drawPlot, this);
// sampling size of input function
contour.SetFirstGrid(inputGridSize,inputGridSize);
// this is the drawing resolution of the plot generated
contour.SetSecondaryGrid(drawSize,drawSize);
// set the number of contour planes
numPlanes = 20;
contourInterval = 0.15;
vector<double> vIso(numPlanes);
for (unsigned int i=0;i<vIso.size();i++) {
vIso[i]=(i-vIso.size()/2.0)*contourInterval;
}
contour.SetPlanes(vIso);
}Finally, in the draw() function you generate and draw the contour plot with one call.
void ofApp::draw(){
// this calculates and draws the contour plot
// by calling (1) fieldFunction
// and (2) drawPlot
contour.Generate();
}- draw function return float / not int
- example to demonstrate contour-plotting from image
- implementation of ListContour class that hands back full opengl-data of contour planes
- proper header info