2.5 Some Graphics

It is possible to do nicer graphics in Turing than just doing the character graphics we saw in chapter one. In this section we'll look at some of the basics of pixel graphics. There are many more things you can do in Turing, but this will be enough to get you started.

The graphics screen is broken up into dots called pixels. Each one can be specified by a point (x, y) like in mathetmatics. The Turing graphics screen basically represents the first quadrant in the x,y-plane. This means that the lower left corner has coordinates (0, 0). Although this is different than virtually all other programming languages it makes a lot more intuitive sense. Here are some of the predefined graphics procedures.

maxx

This procedure gives the maximum possible value for x.

maxy

This procedure gives the maximum possible value for y.

drawdot

This procedure is used to color one of the pixels (dots) on the screen. There are 3 parameters for this procedure. You need to specify the x-coordinate, the y-coordinate and the colour for the dot.

drawline

This procedure is used to draw a line from one specified point to another in a given colour. It has 5 parameters. The first two are the x and y coordinates of the first point. The next two are for the x and y coordinates of the second point. The last parameter is for the colour of the line.

drawbox

This procedure is used to draw a rectangle (box) You specify parameters is the same way as for drawline. The first point is the lower left corner of the box. The second point is the upper right corner of the box.

Let's look at an example using these procedures:

% draw dots at points (100, 50) and (250, 200) in brown % the dots are "very" small drawdot(100, 50, brown) drawdot(250, 200, brown) % draw a line in blue from (300, 250) to (320, 120) drawline(300, 250, 320, 120, blue) % draw a rectangle with lower left at (10, 20) in green % with a width of 100 and height of 200 drawbox(10, 20, 110, 220, green) % draw a rectangle in black with a diagonal in red drawbox(400, 50, 600, 175, black) drawline(400, 50, 600, 175, red)

Here is what the output window will look like:

drawoval

This procedure is used to draw circles and ellipses. It has 5 parameters. The first two parameters represent the x and y coordinates of the centre of the oval. The next two parameters are the x radius and the y radius. If those two values are the same then you will draw a circle. The last parameter is the colour of the oval.

drawfill

So far all our drawings have been simple outlines. It is possible to fill shapes as well. If you have an area enclosed by a border of a single colour then you can fill the inside of that area with a colour. The drawfill procedure takes 4 parameters. The first two are the x and y coordinates of a point inside the area to be filled. The third parameter is the colour to fill with. The last parameter is the color of the border.

drawfillbox

This procedure is exactly the same as drawbox except that the box will be filled with the colour.

drawfilloval

This procedure is exactly the same as drawoval except that the oval will be filled with the colour.

Here is an example with these new procedures:

% draw a blue circle with centre (100, 50) and a radius of 49 drawoval(100, 50, 49, 49, blue) % draw a cyan ellipse drawoval(100, 150, 100, 30, cyan) % draw a yellow triangle drawline(100, 200, 150, 200, yellow) drawline(100, 200, 100, 275, yellow) drawline(100, 275, 150, 200, yellow) % fill the inside of the triangle with red drawfill(120, 210, red, yellow) % draw a solid green rectangle drawfillbox(300, 50, 500, 100, green) % draw a solid magenta circle, centre(300, 200) and radius 75 drawfilloval(300, 200, 75, 75, magenta)

The output window will be:

Exercise 2.5

Write a program that will put four filled squares with sides of length 100 at the four corners of the output window.

Write a program that will produce the five Olympic rings.

Write a program that will draw a house with the sun up in the sky. Draw rays coming from the sun.