Very impressive! I get very excited when I see processing sketches that are more than toys. Your sketch could actually be used for teaching pi/ circumference, area, etc.
Kudos to you!

Dennis

Numbers in green do not display correctly over 100.

Some notes from the geometry app you created and I have slightly modified:

//based on http://openprocessing.org/visuals/?visualID=18290
//Thomas O Fredericks
/*

ideas:
*load images in background to measure area/ distance/
*use for triangulating on maps (where are you, game)
*generate questions for users, calculate missing value based on randomly generated cirles
and triangles


issues:
green numbers over 100 not displayed correctly

exercise ideas:
*calculate the number of X sized triangles that can fit
*squares/ rectangles
*3D volumes
*display area of circle
*dispaly formula calculating circum/ hypotenuse/etc.
*display area of triangle
*change color of background based on x,y value or area of triangle: background(draggedX,draggedY,0);//to change up the colors
(fixes the green number over 100 not working)

*/

PFont font;
int clickX;//when clicking on background
int clickY;
int draggedX;
int draggedY;
boolean centered;

void setup() {
size(500,500);
font = loadFont("BitstreamVeraSansMono-Roman-24.vlw");
textFont(font,12);
clickX = width/2;//always middle of sketch
clickY = height/2;
centered = true;// circle starts in middle
smooth();
}

void draw() {
background(draggedX,draggedY,0);//to change up the colors
drawStuff();

}

void keyPressed() {

if ( key == 'c' ) {//c key does not apparently do anything
clickX = width/2;
clickY = height/2;
} else if ( key == ' ' ) {//space bar recenters mouse location
clickX = mouseX;
clickY = mouseY;
}


}

void mousePressed() {
if ( centered ) {
draggedX = mouseX;
draggedY = mouseY;
} else {
clickX = mouseX;
clickY = mouseY;
draggedX = mouseX;
draggedY = mouseY;
}

}

void mouseDragged() {
if ( mousePressed ) {
draggedX = mouseX;
draggedY = mouseY;
}

}

void drawStuff() {
stroke(255);//white line hypotenuse
line(clickX,clickY,draggedX,draggedY);
stroke(255,0,0);//red line (red, green, blue)
line(clickX,clickY,clickX,draggedY);
stroke(0,255,0);//green line (red, green, blue)
line(clickX,draggedY,draggedX,draggedY);


int distance = (int)dist(clickX,clickY,draggedX,draggedY);
float angle = atan2(draggedY-clickY,draggedX- clickX);
if (angle < 0 ) angle = angle + TWO_PI;
noFill();

stroke(0,0,127);
ellipse(clickX,clickY,distance*2,distance*2);
stroke(255,0,255);
arc(clickX,clickY,distance*2,distance*2,0,angle);
stroke(0,0,255);
arc(clickX,clickY,distance*2,distance*2,TWO_PI+angle,TWO_PI);
fill(255,0,255);
float x = cos(angle/2) * distance + clickX + 5;
float y = sin(angle/2) * distance + clickY + 5;
noStroke();
rect(x,y,35,10);
fill(0);
textAlign(LEFT,TOP);
text(angle,x,y);

fill(255);
noStroke();
rect((clickX-draggedX)/2+draggedX,(clickY-draggedY)/2+draggedY,25,10);
fill(0);
textAlign(LEFT,TOP);

text(distance,(clickX-draggedX)/2+draggedX,(clickY-draggedY)/2+draggedY);

fill(255,0,0);
distance = (int)dist(clickX,clickY,clickX,draggedY);

noStroke();
rect(clickX,(clickY-draggedY)/2+draggedY,15,10);
fill(0);
textAlign(LEFT,TOP);

text(distance,clickX, (clickY-draggedY)/2+draggedY);
fill(0,255,0);
distance = (int)dist(clickX,draggedY,draggedX,draggedY);

noStroke();
rect((clickX-draggedX)/2+draggedX ,draggedY,15,10);
fill(0);//this the green line
textAlign(LEFT,TOP);

text(distance,(clickX-draggedX)/2+draggedX ,draggedY);

}