Rendering a CG Scene - An Introduction to Computer Graphics for Artists - page 214

Chapter 12
Rendering a CG Scene

12.1 Introduction

Rendering is the process by which your 3D data is turned into a 2D image. It is similar
to what happens when a camera takes a photograph, but with a rendering, there is no
camera, no light, and nothing to see. Instead, virtual objects are lit by virtual lights and
then viewed through a virtual lens of a virtual camera. All of these things are defi ned
for the renderer, so that it knows what to do with them during the rendering process.
There are two primary types of renderers, also called rendering engines. These are
rasterizer and ray-tracing engines. A third type that produces high quality results is a
path tracer. Each of these renderers can be used to render images off-line or in-line.
An off-line render is an image that is made and stored immediately on a hard drive,
rather than being sent to a screen without storing the image, also called a frame . An
in-line renderer is also called a real-time renderer, or RT renderer for short.
A real-time renderer renders images directly to the screen without saving them to
disk. It does this rapidly so that 3D content may be viewed interactively. Off-line
renderers produce higher quality renders than in-line renderers, but they are much
slower, making it impossible to render changes to a scene in real-time. “Real-time”
is defi ned as a number of frames displayed per second for the appearance of natu-
ralistic motion. Feature fi lms are shot at 24 frames per second, but video games
usually display between 30 and 60 frames a second.

12.2 Real Time and Pre-rendered Graphics

All real time 3D games presently use rasterizer renderers, though there are some
real time ray tracers and path tracers currently in production (Bikker 2012 ). The
primary difference between the way a rasterizer and a ray tracer works is how each
projects a 3D scene onto a 2D plane.