Trying to make a simple graph (and failing)

beginners
#1

Hi all,
I’m trying to make a simple, EKG-like graph.

As a first attempt, I’d like to plot mouseY vs. time. I’d like the graph to progress left-to-right, and then restart on the left side of the screen.

My graph right now only draws a small dot (as if it was constantly drawing a segment, then erasing.) Here is the main chunk of code. I gutted the graphics example for a framework.

Why does this code only draw a small red segment instead of constantly adding to a line? I’m coming from Processing, so I may be misinformed about how things are drawn and updated on the screen.

  
	  
  void testApp::draw(){  
     if (i < ofGetScreenWidth() ) {  
		currentTime = ofGetElapsedTimeMillis();  
		  
		if ((currentTime - startTime) > 10) {  
			ofSetLineWidth(5);  
			ofSetHexColor(0xFF0000);  
			ofLine(i,mouseDy, i+10, mouseY);  
			mouseDy = mouseY;  
			startTime = ofGetElapsedTimeMillis();  
			i++;  
		}  
		  
	}  
	  
	else {  
                ofBackground(255,255,255);  
		startTime = ofGetElapsedTimeMillis();  
		currentTime = ofGetElapsedTimeMillis();  
		i = 0;  
	}  
}
#2

I may be wrong, but it’s probably because draw clears the screen every frame. You’re only drawing 1 segment per frame and the previously drawn one is cleared. You would need to put a for loop to draw all segments every frame or set ofSetBackgroundAuto to false so that it doesn’t clear every frame. You should then just do ofBackground(255,255,255) to call “clear”.

#3

Sweet! That fixed it.

I’m getting a strange flicker in my line, but I suppose my kludge-y code is to blame.

Would it be best to use a vector/deque/list to store all of the data and draw it with ofSetBackgroundAuto(true) ?