RENDERING PROCESS:

• Introduction
• Principles
• World structure
• Projection
• Finding walls
• Horizontal intersections
• Vertical intersections

MISCELLANEOUS:

• Glossary
  
• Downloads
  
• Links
  

WHAT IS RAYCASTING ?
OK, let's imagine that you're stood in the centre of a field. You can see trees, hedges and grass. You look up and see the sky and the Sun, birds gliding overhead. You can see those things because rays of light, usually from the Sun, bounce off objects and into your eye (to put it rather crudely and simply :) Now, imagine if it was the other way around (as some early Greek scientist thought...) Imagine that your eyes cast invisible rays (not of light, but at the same speed) out until they hit something. When one of them encounters an object, it will send information, such as it's distance, back to you. Each ray's information is then compiled into some sort of order and sent to your brain, producing an image that gives a visual appearance of your surrounding environment.

Although impractical in real-life, this is exactly what happens in a raycasting world. The analogy above has hopefully made clear the idea behind raycasting; if not, then just mail me. I'll now run through some conventions that we'll use during these pages.

SOME CONVENTIONS:
This one was inevitable: coordinates. We need a coordinate system for our worlds and engine. You'll all be familiar with the Cartesian coordinate system (named after Rene Descartes), right ? You know, the one that gives points (vertices to be technical :) as (x, y) ? On paper, X usually runs horizontally across the paper, and Y normally goes vertically up and down the paper. The origin is where the two axis intersect. The X axis normally increases to the right (ie. +1, +2, +3...) and decreases to the left (ie. -1, -2, -3...). Y is usually the same, except it increases going up, and decreases going down. The point (0,0) is where the two axis intersect each other, and is called the origin. This is illustrated in fig3:

fig3: The basic Cartesian coordinate system

For our engine we will change round the Y axis, so that it is increasing downwards and we'll also ignore the negative values on all axes (basically, it's so that the world can be stored as an array of cells, and can be indexed easier; the next step covers the details).

We also need to define direction. For our purposes, we will have 0 degrees facing east, 90 degrees facing north, etc. This needn't be so, any kind of system would do as long as you're consistent in its use, although it's not recommended you use another system because it's fiddly :) The reason for choosing this orientation is discussed in later pages, but for now be content with knowing it's a speed-up and simplifies rendering a little. Anyhow, the two systems that my documentation uses are illustrated in fig4:

fig4: Our systems of direction

CONCLUSION:
This was a very basic introduction, but I hope I've given you sufficient background knowledge so that you have no problems understanding the next sections. We'll be moving on to raycasting worlds (maps is probably a more accurate term) next, where you'll see some of the stuff above being applied.

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