The most effective way to learn something is to do it. These "Getting Started" recipes show how to build 3-D worlds using the Acorn language and its accompanying Type libraries. Each recipe focuses on a specific world-building goal, explaining key concepts using code examples. The recipes become progressively more advanced, building on concepts covered earlier.

To "cook" these recipes, you will need the Pegasus 3D browser, a text editor (e.g., Notepad++), and access to the Internet.

Goal

This first recipe offers a twist on a venerable programming language tradition: showing how to use a language to print out the text "Hello, World!" The twist is that instead of printing out text, we show how to make Acorn render a 3-D model of the world we call Earth.

Recipe

1. On an HTTP server, or your PC, create a new folder called 'helloworld'.
2. Copy into the new folder the following files retrieved from http:://ddd.pegasus3d.com/helloworld:
   • helloworld.acn
   • earth.jpg
   • texture_shader.acn
3. Run the Pegasus3D browser and specify the location of your helloworld folder (e.g., http://ddd.yourserver.com/helloworld or file:///yourfolder).
4. When you see your Earth displayed by the browser, feel free to greet it enthusiastically with "Hello, World!".

How it works

'helloworld.acn' is an Acorn program (Acorn programs use the extension '.acn'). When you open the 'helloworld.acn' program using a text editor, you will see this code:

$ = +World
	scene: +Group
		parts: +List <<
			+Shape.Sphere(1.0)
				shader: TextureMaterial
				image: @'earth.jpg'

Acorn programs look like outlines, with indented lines belonging to the line they are indented under. Indentations at the start of each line must be created using tabs. Each line is a distinct statement, an instruction to the browser on how to set up the world.

This is what this program does:

• The first line creates a new World ('+' means 'new'). A World is a container that organizes everything about a 3-D world. The newly created world is stored in the global variable $, which represents the current world that the Pegasus browser should render.

  All indented lines that follow add information about the new world we are creating. Acorn calls these indented lines a "this" block.

• The next line creates a new Group that will specify all the object's in our world's scene. This group is assigned to the world's 'scene' property. Notice that once again the lines under this statement are indented, which means all those lines apply to the world's scene group. This is a second 'this' block found inside the world's 'this' block.
• The third line creates a new List, which is assigned to the group's 'parts' property. The '<<' operator ensures that every listed part that follows is appended to this list.
• The next line creates a new spherical Shape, whose radius size is 1 meter. This is the shape we use for our Earth. The lines that follow specify the properties for this shape:
  • The shape's shader describes how to paint a colored skin onto our spherical shape. In this case, the '@' operator indicates that we should use an Acorn program found at the specified URL. This program defines a Shader able to wrap a colored picture around the sphere.
  • The shape's texture property specifies the colored picture we want to wrap around the sphere. The picture is a JPEG image found on the Internet at the specified URL. It depicts the continents and oceans of Earth.

Variations

Many simple changes can be made to spice up this simple world. For example:

• To change the size of the Earth, alter the helloworld.acn program to change the sphere's radius from 1.0 to 2.0. Then re-run the browser. The size of the displayed world will double.
• To make the Earth look like another celestial body, just alter the texture: Put an image file for the Moon (moon.jpg) in your 'helloworld' folder, change the name of the texture's image file in the helloworld.acn program, and re-run the browser. Voila, impact craters!

Using subsequent recipes, more sophisticated capabilities can be implemented. For example:

• Alter the camera's position property to move it to a different position. If you move it further back to (0., 0., 20.0) the earth will appear smaller (as it is further away). Similarly, change the 'lookat' property to make the camera look in a different direction.
• Add other planets, the moon or the sun to the scene.
• Start the earth spinning. Orbit it around a sun.
• Create a star field background.
• Create a controllable camera, allowing you to move around the scene.