INTRODUCTION TO 3DMichael Heron

INTRODUCTION

For the next three weeks we will be talking about 3D graphics. Specifically, 3D graphics using the open source

blender package. Module will concentrate on technical content.

I have absolutely no artistic skill in the slightest. Seriously.

Content time broken up into: Two lectures One tutorial One lab prep Four hour lab slot

GRAPHICS

Graphical images on a computer monitor are made up of 2D arrays of pixels. The number of pixels in that array is dependant

on the system’s resolution. Pixels represent a single element of an

image. Represented by a colour code.

Pixels have a depth. Represents the expressive palette of colours. 8 bit depth represents 256 colours 24 bit represents 16.8 million colours

COLOUR REPRESENTATION

Colours are usually represented by an RGB value. An array of three digits corresponding to the

blend of colours. An RGB value of {0,0,0} represents white. An RGB value of {255,255,255} represents

black. Other colours made up of points in-between.

4-BIT COLOUR

8-BIT COLOUR PALETTE

© Lucasarts, 1990

24-BIT COLOUR PALETTE

© Lucasarts, 2009

DISPLAYING GRAPHICAL INFORMATION

Graphics are displayed on a computer monitor using rasters. Lines of pixels.

CRT monitors make use of electron guns to display images on the screen. Three guns (red, green, blue) Guns fire beams at the phosphor coating on the

inside of the monitor. This occurs many times per second.

Governed by the monitor’s refresh rate.

DISPLAYING GRAPHICAL INFORMATION

An LCD works somewhat differently. A backlight is used to create light This light passes through two substrates of

polarised glass. While this is happening, an electrical current

causes the crystals within the substrates to align. The combination of these substrates allows for the

desired colours to appear at the appropriate point.

There are other ways too Not important at this time.

REPRESENTING GRAPHICS (2D)

Two main way of representing graphics in a computer. Rasters, comprised of arrays of pixels. Vectors, comprised of collections of objects

expressed as mathematical formulae. Rasters used to represent photographs and

other such bitmaps. Vectors used to represent more asbtract

models.

REPRESENTING GRAPHICS (3D)

In three dimensions, vectors are used almost exclusively for representing shapes. Images built up of collections of vertices, points,

and polygons.

DIFFERENCES IN REPRESENTATION

2D Images Raster

Permits great amounts of detail but no representation of relationship between objects.

Substantial file size Vector

Permits relationship of objects. Minimal details permitted

Difficult to represent details using basic shapes

Several trade offs Processing Power Realism Modifiability Expressive Potential.

3D GRAPHICS

Complex 3D scenes can be created as 2D images. Often done using ray-tracing or other technologies.

Not real-time

Goal of 3D graphics is to permit photorealistic representations of complex spatial topographies. Difficult task Requires much investment in building

environments and objects within them Many applications require real-time rendering.

Games

PHOTOREALISM

3D Graphics seeks to achieve photrealism by: Vector representation of 3D Objects Texturing of 3D objects in materials Interaction of light on objects

Shadows Reflections Colour Glare

Photorealism is important for many contexts. Simulation, entertainment, research, medical

teaching

3D ON A COMPUTER

Not possible to show 3D images on a computer. Monitor is an inherently 2D device.

Techniques are used to simulate the appearance of three dimensions. Use of perspective, layering, projection of a

plane onto a fixed view. Many different interacting parts.

3D MODELLING

3D Modelling is a multi-stage process. Representation

Build a model of 3D Objects Shapes Surface textures

Sometimes using bitmaps.

Rendering Geometric translations Projection to 2D Light representation

THE CARTESIAN PLANE

SIMPLE 3D OBJECT

(x1,y1,z1) (x2,y2,z2)

(x3,y3,z3)(x4,y4,z4)

(x5,y5,z5) (x6,y6,z6)

(x7,y7,z7)(x8,y8,z8)

© Glenn Rowe

MORE COMPLEX REPRESENTATIONS

http://www.fallingpixel.com/3d-models/13227

3D REPRESENTATIONS

Complex shapes represented by polygons Triangles and Rectangles mostly

Number of polygons defines the accuracy of the representation

http://www.nvnews.net/reviews/evolva_preview.shtml

TRANSFORMATIONS

Transformations used in 3D to manipulate images. Three main transformations used in Blender.

Grab (translate) Used to move shapes around fixed axis

Rotate Used to rotate shapes around a fixed axis

Scale Used to scale shapes up or down

Underlying representation done using matrix manipulation.

PROJECTION

Projection is the process that transforms 3D objects onto a 2D plane. Three co-ordinate models.

Local, defines the shape’s vertexes World space, defines the shape in relation to other

shapes. Viewing space, defines the location and size of the

shape when displayed on the monitor.

Process turns {x,y,z} into just {x,y}

PROJECTION STYLES

Parallel Projection Shows relationship between objects Not realistic

View plane

3D object

PROJECTION STYLES

Perspective Projection Represents objects more realistically by

converging vertexes at a point. Foreshortening permits perspective.

View plane

3D object

Centre of projection

PROJECTION

Both assume a camera location. The camera defines our view on the world.

To change the view of an object, we can: Move the camera Move the object.

Must get our heads around a viewport that has no fixed representation in the world space.

SUMMARY

Next three weeks about 3D graphics. Using Blender.

3D Graphics consist of Representation of objects Representation of a world Representation of a view port Rendering

Complex transforms applied to turn 3D representation into 2D view.