I'm trying to display a flowchart via JGraphx, and I need a parallelogram for input/output block. But JGraphx doesn't seem to know "shape=parallelogram". It seems odd not to have a parallelogram in a library for graphs and flowcharts (and it even has "actor" shape, how come it doesn't have a parallelogram?). Maybe it's only named some other way? Or in the case there is indeed no predefined parallelogram shape, what do I do to make a vertex into parallelogram?
Finally, I've found a way to make a parallelogram, yay! Here is how I made it work.
First of all, to make a custom shape I had to create my own class extending mxBasicShape and override the createShape method.
public class Parallelogram extends mxBasicShape {
public Shape createShape(mxGraphics2DCanvas canvas, mxCellState state){
mxCell cell = (mxCell)state.getCell();
Polygon polygon = new Polygon();
if(cell != null && cell.getGeometry() != null) {
mxGeometry g = cell.getGeometry();
int dx = (int) (cell.getGeometry().getHeight()/4.0);
polygon.addPoint((int)(g.getX()+dx), (int)g.getY());
polygon.addPoint((int)(g.getX()+g.getWidth()+dx), (int)g.getY());
polygon.addPoint((int)(g.getX()+g.getWidth()-dx), (int)(g.getY()+g.getHeight()));
polygon.addPoint((int)((int)g.getX()-dx), (int)(g.getY()+g.getHeight()));
}
return polygon;
}
}
The second step is adding it to a list of shapes which appeared to be stored in mxGraphics2DCanvas.
mxGraphics2DCanvas.putShape("parallelogram", new Parallelogram());
And now "shape=parallelogram" works just fine!
UPD
It appeared creating just a shape is not enough and a perimeter is also to be created. This is how I've done it:
public class ParallelogramPerimeter implements mxPerimeterFunction {
@Override
public mxPoint apply(mxRectangle bounds, mxCellState vertex, mxPoint next,
boolean orthogonal) {
double cx = bounds.getCenterX();
double cy = bounds.getCenterY();
double nx = next.getX();
double ny = next.getY();
double pi = Math.PI;
double pi2 = Math.PI/2.0;
double h = bounds.getHeight();
double w = bounds.getWidth();
double alpha = Math.atan2(h/2.0, w/2.0+h/4.0);
double beta = Math.atan2(h/2.0, w/2.0-h/4.0);
double t = Math.atan2(ny-cy, nx-cx);
mxPoint p = new mxPoint();
//Left
if (t > pi - alpha || t < (-pi)+beta){
Line border = new Line(cx-w/2.0+h/4.0, cy-h/2.0, cx-w/2.0-h/4.0, cy+h/2.0);
Line line = new Line(cx, cy, nx, ny);
p = Line.intersection(border, line);
}
//Top
else if (t > (-pi)+beta && t < (0-alpha)){
p.setY(cy-h/2.0);
p.setX(cx + h/2.0*Math.tan(pi2+t));
}
//Right
else if (t > (0-alpha) && t < beta){
Line border = new Line(cx+w/2.0+h/4.0, cy-h/2.0, cx+w/2.0-h/4.0, cy+h/2.0);
Line line = new Line(cx, cy, nx, ny);
p = Line.intersection(border, line);
}
//Bottom
else {
p.setY(cy+h/2.0);
p.setX(cx + h/2.0*Math.tan(pi2-t));
}
if (orthogonal){
//Top
if (nx >= cx-w/2.0+h/4.0 && nx <= cx+w/2.0+h/4.0 && ny <= cy-h/2.0){
p.setX(nx);
}
//Bottom
else if (nx >= cx - w/2.0-h/4.0 && nx <= cx+w/2.0-h/4.0 && ny >= cy+h/2.0){
p.setX(nx);
}
//Left or right
else{
Line left = new Line(cx-w/2.0+h/4.0, cy-h/2.0, cx-w/2.0-h/4.0, cy+h/2.0);
Line right = new Line(cx+w/2.0+h/4.0, cy-h/2.0, cx+w/2.0-h/4.0, cy+h/2.0);
p = left.projection(nx, ny);
mxPoint p1 = right.projection(nx, ny);
boolean r = false;
if (distance(nx, ny, p.getX(), p.getY()) > distance(nx, ny, p1.getX(), p1.getY()))
{
p = p1;
r = true;
}
//Upper corners
if (p.getY() < cy-h/2.0){
p.setY(cy-h/2.0);
if(r){
p.setX(cx+w/2.0+h/4.0);
}
else
{
p.setX(cx-w/2.0+h/4.0);
}
}
//Lower corners
else if (p.getY() > cy+h/2.0){
p.setY(cy+h/2.0);
if(r){
p.setX(cx+w/2.0-h/4.0);
}
else
{
p.setX(cx-w/2.0-h/4.0);
}
}
}
}
return p;
}
private double distance(double x1, double y1, double x2, double y2){
return Math.sqrt(Math.pow(x2-x1, 2)+Math.pow(y2-y1, 2));
}
}
class Line{
private double a;
private double b;
private double c;
Line(double x1, double y1, double x2, double y2){
a = y1-y2;
b = x2-x1;
c = x1*y2-x2*y1;
}
private Line(double a, double b, double c){
this.a = a;
this.b = b;
this.c = c;
}
static private double determinant(double i, double j, double k, double l){
return i*l - k*j;
}
static mxPoint intersection(Line first, Line second){
double x,y;
double denominator = determinant(first.a, first.b, second.a, second.b);
x = 0 - determinant(first.c, first.b, second.c, second.b)/denominator;
y = 0 - determinant(first.a, first.c, second.a, second.c)/denominator;
return new mxPoint(x,y);
}
mxPoint projection(double x, double y){
double a,b,c;
if (this.b!=0){
a=1;
b=-(this.a*a)/this.b;
}
else{
b = 1;
a=-(this.b*b)/this.a;
}
c = -(a*x+b*y);
Line line = new Line(a,b,c);
return intersection(this, line);
}
}
Then I had to add it to the perimeters in use, whose list appeared to be not in the same place as with shapes, but in mxStyleRegistry:
mxStyleRegistry.putValue("parallelogramPerimeter", new ParallelogramPerimeter());
And finally I've used "shape=parallelogram;perimeter=parallelogramPerimeter" for a style, which now works not only for displaying the parallelogram, but also for connecting edges to it properly.