Flags with Repeats Tutorial

Flags Tutorials

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Repeats

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We can repeat a statement or block of statements with a for loop. The simplest for loops take the following form:

The control variable i takes every value 0,1,2..9 in turn. We can use the value of i inside the loop if required.

Bahrain

The flag of Bahrain has a five irregular pentagons on a red background.

Each pentagon can be represented by five points such as (0,0), (64,0) (100,15) (64,31) and (0,31).

Flag of Bahrain

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static void drawFlag(Graphics2D g) { //Flag of Bahrain //Define a pillar as a polygon Polygon pillar = new Polygon( new int[]{0,64,100,64, 0}, new int[]{0, 0, 15,31,31}, 5); //Do the background g.setColor(Color.red); g.fillRect(0,0,250,155); g.setColor(Color.white); for (int i=0;i<2;i++) { //Draw the pillar g.fillPolygon(pillar); g.translate(0,31); } }

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Qatar

Consider the neighbouring state Qatar.

• 9 pillars, each pillar is 17 pixels below the previous.
• The five coordinates of the top pillar are (0,0) (84,0) (125,9) (84,17), (0,17)
• Use RGB(128,0,0) for the less jaunty red.

Flag of Qatar

The need for a loop becomes even more obvious for this flag.

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static void drawFlag(Graphics2D g) { g.setColor(new Color(128,0,0)); g.fillRect(0,0,300,153); }

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India

The flag of India is 306 by 204. The orange, white and green stripes are 306 by 68. The wheel has radius 30.

The flag of India includes a wheel with 24 spokes, the spokes are 2*pi/24 radians apart.

The code given draws only three of the spokes - we could copy and paste - but it would be much better to use a loop.

We have not really done India justice here - the actual flag is much more elegant, the spokes taper and the rim includes decoration. Nevertheless - we apologize to the sub-continent and move on.

Flag of India

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static void drawFlag(Graphics2D g) { g.setRenderingHint( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g.setColor(Color.orange); g.fillRect(0, 0,306,68); g.setColor(Color.green); g.fillRect(0,134,306,68); g.setColor(Color.blue); g.setStroke(new BasicStroke(2,0,0)); g.drawOval(123,72,60,60); g.translate(153,102); g.rotate(2*Math.PI/24); g.drawLine(0,0,0,30); g.rotate(2*Math.PI/24); g.drawLine(0,0,0,30); g.rotate(2*Math.PI/24); g.drawLine(0,0,0,30); }

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Namibia

Each the rightmost triangle has coordinates (19,5) (29,0) (19,-5) relative to the centre of the star burst - which is at (60,60).

Notice that only two of the 12 triangles are drawn by the example code. Also note that the colors are mixed up.

We can use the method g.rotate(Math.PI/6) to repeat the triangles of the star-burst for Namibia.

• The yellow circle has radius 16
• The triangles are partially covered by a blue circle of radius 20
• The whole flag is 300 by 200
• You must set the white part of the flag white

Flag of Namibia

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static void drawFlag(Graphics2D g) { g.setRenderingHint( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g.setColor(Color.green); g.fillPolygon(new Polygon( new int[]{0,240,0}, new int[]{0,0,160},3)); g.setColor(Color.red); g.fillPolygon(new Polygon( new int[]{60,300,300}, new int[]{200,40,200},3)); g.setStroke(new BasicStroke(42)); g.setColor(Color.blue); g.drawLine(0,200,300,0); g.translate(60,60); g.setColor(Color.black); Polygon tri = new Polygon( new int[]{19,29,19}, new int[]{ 5, 0,-5},3); g.fillPolygon(tri); g.rotate(Math.PI/6); g.fillPolygon(tri); }

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European Union

Flag of European Union

We need the trigonometry functions cos and sin to draw flags in a circle.

• There are 12 stars
• The flag is 250 by 180
• The stars centers are 64 from the center
• The coordinates at 30^o from the x-axis (East) are 64*cos(30), 64*sin(30).
• Each star has radius 12.5

Help with Stars

Look at the original program

 g.setColor(Color.yellow);
 for (int i=0;i<9;i++){
   double a = Math.PI*2*i/9;
   g.translate( 100*Math.cos(a), 100*Math.sin(a));
   g.fillPolygon(star);
   g.translate(-100*Math.cos(a),-100*Math.sin(a));
 }

• The circle of stars is currently centered at the origin.
  • You can move this by adding a translate call after the setColor line

g.translate(100,100);

• The number of stars filled is 9; you want 12
  • Change this number in the for line
  • Change this number in the calculation of the angle a
• The radius of the circle of stars is 100; you want it to be 64
  • The number 100 shows up in the translate methods four times

Radians

The sin and cos functions in Java are called Math.sin and Math.cos. They expect radians as input. 360^o is 2*Math.PI in radians.

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static void drawFlag(Graphics2D g) { Polygon star = new Polygon( new int[]{0 ,3 ,12,5 ,8,0,-8,-5,-12,-3}, new int[]{-13,-4,-4,2 ,11,5,11,2,-4,-4},10); g.setColor(Color.blue); g.fillRect(0,0,500,350); g.setColor(Color.yellow); for (int i=0;i<9;i++) { double a = Math.PI*2*i/9; g.translate( 100*Math.cos(a), 100*Math.sin(a)); g.fillPolygon(star); g.translate(-100*Math.cos(a),-100*Math.sin(a)); } }

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Flags Tutorials

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