C++:Flags with Repeats Tutorial

Flags Tutorials

Rectangles

Lines

Polygons

Stars

Repeats

Methods

Hard Problems

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), (128,0) (200,31) (128,62) and (0,62).

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static void drawFlag(Image& g){ //Do the background g.fillColor("red"); g.draw(DrawableRectangle(0,0,500,310)); g.fillColor("white"); // Define the polygon pillar std::list<Coordinate> pillar; pillar.push_back(Coordinate(0,0)); pillar.push_back(Coordinate(128,0)); pillar.push_back(Coordinate(200,31)); pillar.push_back(Coordinate(128,62)); pillar.push_back(Coordinate(0,62)); // Build up a list of Drawable std::list<Magick::Drawable> dl; dl.push_back(DrawablePushGraphicContext()); for (int i=0;i<2;i++){ //Draw the pillar dl.push_back(DrawablePolygon(pillar)); dl.push_back(DrawableTranslation(0,62)); } dl.push_back(DrawablePopGraphicContext()); g.draw(dl); }

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Qatar

Neighbouring state Qatar has 9 pillars, each pillar is 34 units below the previous. Use RGB(128,0,0) for the less jaunty red.

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

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static void drawFlag(Image& g){ g.fillColor(ColorRGB(0.5,0,0)); g.draw(DrawableRectangle(0,0,600,306)); }

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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.

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static void drawFlag(Image& g){ g.fillColor("orange"); g.draw(DrawableRectangle(0,0,306,68)); g.fillColor("white"); g.draw(DrawableRectangle(0,68,306,136)); g.fillColor("green"); g.draw(DrawableRectangle(0,136,306,204)); g.fillColor("white"); g.strokeColor("blue"); g.strokeWidth(2); std::list<Magick::Drawable> dl; dl.push_back(DrawablePushGraphicContext()); dl.push_back(DrawableCircle(150,100,150,70)); dl.push_back(DrawableTranslation(150,100)); dl.push_back(DrawableLine(0,0,30,0)); dl.push_back(DrawableRotation(15)); dl.push_back(DrawableLine(0,0,30,0)); dl.push_back(DrawableRotation(15)); dl.push_back(DrawableLine(0,0,30,0)); dl.push_back(DrawableRotation(15)); dl.push_back(DrawablePopGraphicContext()); g.draw(dl); }

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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.

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static void drawFlag(Image& g){ std::list<Coordinate> top; top.push_back(Coordinate(0,0)); top.push_back(Coordinate(240,0)); top.push_back(Coordinate(0,160)); std::list<Coordinate> btm; btm.push_back(Coordinate(60,200)); btm.push_back(Coordinate(300,40)); btm.push_back(Coordinate(300,200)); std::list<Coordinate> ray; ray.push_back(Coordinate(19,5)); ray.push_back(Coordinate(29,0)); ray.push_back(Coordinate(19,-5)); // Build up a list of Drawable std::list<Magick::Drawable> dl; dl.push_back(DrawablePushGraphicContext()); dl.push_back(DrawableFillColor("green")); dl.push_back(DrawablePolygon(top)); dl.push_back(DrawableFillColor("red")); dl.push_back(DrawablePolygon(btm)); dl.push_back(DrawableStrokeColor("blue")); dl.push_back(DrawableStrokeWidth(42)); dl.push_back(DrawableLine(0,200,300,0)); dl.push_back(DrawableStrokeColor("black")); dl.push_back(DrawableStrokeWidth(0)); dl.push_back(DrawableFillColor("black")); dl.push_back(DrawableTranslation(60,60)); dl.push_back(DrawablePolygon(ray)); dl.push_back(DrawableRotation(30)); dl.push_back(DrawablePolygon(ray)); dl.push_back(DrawablePopGraphicContext()); g.draw(dl); }

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European Union

We need the trigonometry functions cos and sin to draw flags in a circle. The coordinates of a point on a circle radius 125 at 30° from the x-axis (East) these are 125*cos(30), 125*sin(30).

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static void drawFlag(Image& g){ // Define the polygon star std::list<Coordinate> star; star.push_back(Coordinate(0,-25)); star.push_back(Coordinate(6,-8)); star.push_back(Coordinate(24,-8)); star.push_back(Coordinate(9,3)); star.push_back(Coordinate(15,20)); star.push_back(Coordinate(0,9)); star.push_back(Coordinate(-15,20)); star.push_back(Coordinate(-9,3)); star.push_back(Coordinate(-24,-8)); star.push_back(Coordinate(-6,-8)); // Build up a list of Drawable std::list<Magick::Drawable> dl; dl.push_back(DrawablePushGraphicContext()); dl.push_back(DrawableFillColor("blue")); dl.push_back(DrawableRectangle(0,0,500,350)); dl.push_back(DrawableFillColor("yellow")); for (int i=0;i<9;i++){ double th = PI*2*i/9; dl.push_back(DrawableTranslation(125*cos(th), 125*sin(th))); dl.push_back(DrawablePolygon(star)); dl.push_back(DrawableTranslation(-125*cos(th), -125*sin(th))); } dl.push_back(DrawablePopGraphicContext()); g.draw(dl); }

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