Trouble making a custom line graph

I am trying to build a custom line graph in a custom GUI.
What I thought of doing was to use the drawline command to draw the line graph in increments. the problem is everytime it draws the next increment of the line the previous one disappears and instead of a line I see a worm moving!! . here is the code that I used in the ondraw attribute of the graph:

treenode view = c;
treenode waiting_area = node(">viewfocus+",view);

double yvalue = getlabelnum(waiting_area,"Avg_WTBS");
double xvalue = getlabelnum(waiting_area,"PatientNumber")*.1;
int lastx = getlabelnum(centerobject(waiting_area,1),"lastx");
int lasty = getlabelnum(centerobject(waiting_area,1),"lasty");

drawline(view,lastx,lasty,0,xvalue+1,yvalue,0,1,0, 1);

setlabelnum(centerobject(waiting_area,1),"lastx",x value + 1);
setlabelnum(centerobject(waiting_area,1),"lasty",y value);

Hello mearjun,

You are drawing one (moving) point every time. Every time the OnDraw code is refreshed it starts with a blank sheet. If you want to draw 10 line segments, you will have to call the drawline command 10 times (you can use a for loop). For every segment you have to determine the start and end point.

It could look something like:

treenode view = c;
treenode waiting_area = node(">viewfocus+",view);

double yvalue = getlabelnum(waiting_area,"Avg_WTBS");
double xvalue = getlabelnum(waiting_area,"PatientNumber")*.1;
int lastx = getlabelnum(centerobject(waiting_area,1),"lastx");
int lasty = getlabelnum(centerobject(waiting_area,1),"lasty");

int nrOfLines = 10;

for( int x = 1; x <= nrOfLines; x++ )
{
drawline(view,lastx,lasty,0,xvalue+1,yvalue,0,1,0, 1);
lastx++; // adds 1 to the lastx value
}

Esther

Thanks for answering but I am not clear yet..Here is what I am trying to do. I want that whenever the value of a particular label changes a new point in the graph should be found such that new y is the label value and x increments by 1. When you say that I should use a for loop, how would I have all the possible values of y (label values) at one time ?
Maybe what I need to do is that the line I draw should be a permanent line and the ondraw trigger should not refresh the entire canvas the next time so that a curve is generated with the help of 1000s of small lines.

Hello,

you have to store all the values you want to print in the graph. You can use different methods to store values (table, tracked variables, bundles).

Jörg