grphics01 - introduction to 3d graphics
DESCRIPTION
This is a course on the theoretical underpinnings of 3D Graphics in computing, suitable for students with a suitable grounding in technical computing.TRANSCRIPT
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.