Pentagram: Difference between revisions
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'''The task''': draw (or print) a regular pentagram, in any orientation. Use a different color (or token) for |
'''The task''': draw (or print) a regular pentagram, in any orientation. Use a different color (or token) for |
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stroke and fill. |
stroke and fill, and background. |
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Revision as of 10:06, 22 April 2015
A pentagram is a star polygon, consisting of a central pentagon of which each side forms the base of an isosceles triangle.
The vertex of each triangle, a point of the star, is 36 degrees.
The task: draw (or print) a regular pentagram, in any orientation. Use a different color (or token) for
stroke and fill, and background.
See also
J
Probably the simplest approach is:
<lang j>plot j./2 1 o./180p_1 %~ 72*i. 6</lang>
This will give a pentagram with a blue border and a white interior.
Java
<lang java>import java.awt.*; import java.awt.geom.Path2D; import javax.swing.*;
public class Pentagram extends JPanel {
final double degrees144 = Math.toRadians(144);
public static void main(String[] args) { SwingUtilities.invokeLater(() -> { JFrame f = new JFrame(); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.setTitle("Pentagram"); f.setResizable(false); f.add(new Pentagram(), BorderLayout.CENTER); f.pack(); f.setLocationRelativeTo(null); f.setVisible(true); }); }
public Pentagram() { setPreferredSize(new Dimension(640, 640)); setBackground(Color.white); }
private void drawPentagram(Graphics2D g, int len, int x1, int y1) { double angle = 0;
for (int i = 0; i < 5; i++) { int x2 = x1 + (int) (Math.cos(angle) * len); int y2 = y1 + (int) (Math.sin(-angle) * len); g.drawLine(x1, y1, x2, y2); x1 = x2; y1 = y2; angle -= degrees144; } }
private void fillPentagram(Graphics2D g, int len, int x, int y) { double angle = 0;
Path2D.Float p = new Path2D.Float(); p.moveTo(x, y);
for (int i = 0; i < 10; i++) {
x = x + (int) (Math.cos(angle) * len); y = y + (int) (Math.sin(-angle) * len); p.lineTo(x, y);
angle += (i % 2 == 0 ? 0.5 : -1) * degrees144; }
p.closePath(); g.fill(p); }
@Override public void paintComponent(Graphics gg) { super.paintComponent(gg); Graphics2D g = (Graphics2D) gg;
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g.setStroke(new BasicStroke(5, BasicStroke.CAP_ROUND, 0));
g.setColor(new Color(0xFFD700)); // gold fillPentagram(g, 190, 72, 250);
g.setColor(Color.darkGray); drawPentagram(g, 500, 70, 250); }
}</lang>
PostScript
<lang postscript>%!PS-Adobe-3.0 EPSF %%BoundingBox: 0 0 200 600
/n 5 def % 5-star; can be set to other odd numbers
/s { gsave } def /r { grestore } def /g { .7 setgray } def /t { 100 exch translate } def /p { 180 90 n div sub rotate 0 0 moveto n { 0 160 rlineto 180 180 n div sub rotate } repeat closepath } def
s 570 t p s g eofill r stroke r % even-odd fill s 370 t p s g fill r stroke r % non-zero fill s 170 t p s 2 setlinewidth stroke r g fill r % non-zero, but hide inner strokes
%%EOF</lang>