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Fault Drawing arcs between adjacent edges of a triangle

I am trying to write code to generate random triangles and draw arcs between adjacent edges of a triangle to describe the angle between them. It almost works. But it looks like my math failed somewhere, and in some runs the arcs are not drawn correctly.

Please tell me where I am wrong. Perhaps these lines are factors:

g.draw(new Arc2D.Double(x1-r,y1-r,2*r,2*r,0,a,Arc2D.OPEN)); g.draw(new Arc2D.Double(x2-r,y2-r,2*r,2*r,(180-b),b,Arc2D.OPEN)); g.draw(new Arc2D.Double(x3-r,y3-r,2*r,2*r,-180+a,c,Arc2D.OPEN));

Here is the SSCCE:

  import javax.swing.JComponent; import javax.swing.JFrame; import java.awt.geom.*; import java.awt.*; import java.util.*; class MyCanvas extends JComponent { int a,supb,b,c,length,r; double x1,y1,x2,y2,x3,y3; Random random=new Random(); public MyCanvas(){ a=random.nextInt(80-30)+30; supb=random.nextInt(120-70)+100; b=180-supb; c=180-ab; length=random.nextInt(150-100)+100; x1=0; y1=0; r=20; x2=x1+length; y2=y1; x3=(x1+Math.cos(Math.toRadians(-a))*length); y3=(y1+Math.sin(Math.toRadians(-a))*length); } public void paintComponent(Graphics g2){ Graphics2D g=(Graphics2D) g2; Random random=new Random(); AffineTransform oldt=g.getTransform(); Shape shape=getTriangle(x1,y1,x2,y2,x3,y3); Rectangle2D bounds=shape.getBounds2D(); double height=bounds.getHeight(); double width=bounds.getWidth(); g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON); g.setStroke(new BasicStroke(2.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_BEVEL)); g.translate((this.getWidth() - width) / 2,(this.getHeight() - height) / 2); g.translate(-bounds.getX(),-bounds.getY()); g.draw(shape); g.draw(new Arc2D.Double(x1-r,y1-r,2*r,2*r,0,a,Arc2D.OPEN)); g.draw(new Arc2D.Double(x2-r,y2-r,2*r,2*r,(180-b),b,Arc2D.OPEN)); g.draw(new Arc2D.Double(x3-r,y3-r,2*r,2*r,-180+a,c,Arc2D.OPEN)); g.setTransform(oldt); } private Shape getTriangle(double length,double a,double b,double c){ double x1=0,y1=0,x2,y2,x3,y3; x2=x1+length; y2=y1; x3=(x1+Math.cos(Math.toRadians(-a))*length); y3=(y1+Math.sin(Math.toRadians(-a))*length); return getTriangle(x1,y1,x2,y2,x3,y3); } private Shape getTriangle(double x1,double y1,double x2,double y2,double x3,double y3){ GeneralPath gp=new GeneralPath(); gp.moveTo(x1,y1); gp.lineTo(x2,y2); gp.lineTo(x3,y3); gp.closePath(); return gp; } private void drawArc(Graphics2D g,int x0,int y0,int x1,int y1,int x2,int y2){ int r = (int)Math.sqrt((x1-x0)*(x1-x0) + (y1-y0)*(y1-y0)); int x = x0-r; int y = y0-r; int width = 2*r; int height = 2*r; int startAngle = (int) (180/Math.PI*Math.atan2(y1-y0, x1-x0)); int endAngle = -(int) (180/Math.PI*Math.atan2(y2-y0, x2-x0)); g.drawArc(x, y, width, height, startAngle, endAngle); } } public class TrianglePanel { public static void main(String[] a) { JFrame window = new JFrame(); window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); window.setBounds(30, 30, 300, 300); window.getContentPane().add(new MyCanvas()); window.setVisible(true); } }

These images show the result in two different SSCCE runs: enter image description here

enter image description here

Any help would be appreciated.

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The problem was that you incorrectly calculated the length of the arcs, which would make the second and third angles not obtainable the way you wanted all the time.

 import javax.swing.JComponent; import javax.swing.JFrame; import java.awt.geom.*; import java.awt.*; import java.util.*; class MyCanvas extends JComponent { int a, supb, b, c, length, r; double x1, y1, x2, y2, x3, y3; Random random = new Random(); public MyCanvas() { a = random.nextInt(80 - 30) + 30; supb = random.nextInt(120 - 70) + 100; b = 180 - supb; c = 180 - a - b; length = random.nextInt(150 - 100) + 100; x1 = 0; y1 = 0; r = 20; x2 = x1 + length; y2 = y1; x3 = (x1 + Math.cos(Math.toRadians(-a)) * length); y3 = (y1 + Math.sin(Math.toRadians(-a)) * length); } public void paintComponent(Graphics g2) { float dx1, dy1, ang1, dx2, dy2, ang2, ang3; Graphics2D g = (Graphics2D) g2; AffineTransform oldt = g.getTransform(); Shape shape = getTriangle(x1, y1, x2, y2, x3, y3); Rectangle2D bounds = shape.getBounds2D(); double height = bounds.getHeight(); double width = bounds.getWidth(); g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g.setStroke(new BasicStroke(2.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_BEVEL)); g.translate((this.getWidth() - width) / 2, (this.getHeight() - height) / 2); g.translate(-bounds.getX(), -bounds.getY()); dy1 = (float) (y3 - y1); dx1 = (float) (x3 - x1); ang1 = (float) (Math.atan((float)(dy1 / dx1)) * 180 / Math.PI); ang1 = (float) Math.abs(ang1); dy2 = (float) (y2 - y3); dx2 = (float) (x2 - x3); ang2 = (float) (Math.atan((float)(dy2 / dx2)) * 180 / Math.PI); ang2 = (float) Math.abs(ang2); ang3 = (float) (180-ang2-ang1); g.setColor(Color.BLACK); g.draw(shape); g.setColor(Color.RED); g.draw(new Arc2D.Double(x1 - r, y1 - r, 2 * r, 2 * r, 0, ang1, Arc2D.OPEN)); g.setColor(Color.GREEN); g.draw(new Arc2D.Double(x2 - r, y2 - r, 2 * r, 2 * r, (180 - ang2), ang2, Arc2D.OPEN)); g.setColor(Color.RED); g.draw(new Arc2D.Double(x3 - r, y3 - r, 2 * r, 2 * r, -180 + a, ang3, Arc2D.OPEN)); g.setTransform(oldt); } private Shape getTriangle(double x1, double y1, double x2, double y2, double x3, double y3) { GeneralPath gp = new GeneralPath(); gp.moveTo(x1, y1); gp.lineTo(x2, y2); gp.lineTo(x3, y3); gp.closePath(); return gp; } } public class TrianglePanel { public static void main(String[] a) { JFrame window = new JFrame(); window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); window.setBounds(30, 30, 300, 300); window.getContentPane().add(new MyCanvas()); window.setVisible(true); } }
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Source: https://habr.com/ru/post/1481775/

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