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# GRPHICS02 - Creating 3D Graphics

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This is a course on the theoretical underpinnings of 3D Graphics in computing, suitable for students with a suitable grounding in technical computing.

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### GRPHICS02 - Creating 3D Graphics

1. 1. CREATING A 3D IMAGE Michael Heron
2. 2. INTRODUCTION  In this lecture we are going to look at the process we go through in order to build a 3D image.  At least in theory.  Will need to wait until the lab before we do it For Reals.  Two main techniques for doing this.  Line Mode  Box Mode
3. 3. TERMINOLOGY  Face  A simple shape used to make up a more complex shape.  Also known as a polygon  Vertex  A corner point of a polygon  Edge  A line represented by two connected vertexes
4. 4. CREATING A 3D OBJECT  We need to do several things.  Define the geometry of the shape.  Apply transforms to set  Location  Scale  Rotation  Define surface details.  Textures  We do this for each object in a scene.  We’ll talk about only one.
5. 5. DEFINE THE GEOMETRY  How do we define the geometry?  We choose between two main ways.  Or a hybrid of the two.  First way is to draw each point in the shape.  For large, complex shapes – extremely difficult.  The more polygons we have, the more difficult this becomes.  This is the line mode of drawing shapes.  There be dragons.
6. 6. DEFINE THE GEOMETRY  How do you sculpt an elephant?  You take a block of marble, and chip away all the bits that don’t look like an elephant.  This is the Box Mode of drawing shapes.  Start with an approximate shape.  Usually one of the standard geometric principles.  Manipulate it until it fits your needs.  Or at least, closely approximates your needs.  Recommended approach.
7. 7. DEFINE THE GEOMETRY  A third way is to make use of a representation of a real object.  Requires the use of specialised hard-ware  Which you don’t have.  The method you choose depends on  The nature of the object  Requirements of the model.  A hybrid approach is usually the best  Start with a rough shape, draw extensions to handle fine detail work.
8. 8. 3D REPRESENTATIONAL FORMS  Several ways to represent 3D Geometry:  Polygonal.  Objects approximated by nets of polygons  A polymesh  Bicubic  Objects represented by nets of curved patches.  Constructive Solid Geometry  Constructed from sets of basic geometric shapes  Space subdivision  Ray-tracing  We focus primarily on polygonal today.  Talk about the rest in the next lecture, or thereabouts.
9. 9. SIMPLE POLYMESH (x1,y1,z1) (x2,y2,z2) (x3,y3,z3) (x4,y4,z4) (x5,y5,z5) (x6,y6,z6) (x7,y7,z7)(x8,y8,z8)
10. 10. SIMPLE POLYMESH – LOCAL CO-ORDINATES (0,0,0) (50,0,0) (50,0,50)(0,0,50) (0,50,0) (50,50,0) (50,50,50)
11. 11. SIMPLE POLYMESH - REPRESENTATION object surfaces polygons vertices
12. 12. SIMPLE POLYMESH - REPRESENTATION  Represented by a face-vertex mesh  A list of faces represented by vertexes  A list of the vertexes and what faces they are part of  Co-ordinate space of each vertex.  This provides a mathematical, context independent representation of an object in its own local space.
13. 13. FACE-VERTEX MESH
14. 14. POLYMESH NOTES  Shape is only an approximation for complex images.  Can’t represent a circle.  Can represent something that is almost a circle  Level of approximation dictated by polygon count.  Shading and other detailing approaches can help to hide shape approximations.  Ubiquitous representation.  Graphics cards usually include specialised hardware for rendering large numbers of polygons.
15. 15. DRAWING AN OBJECT  Begin with simple starting shape.  Want to draw a head? Start with a sphere.  Can add a sphere as a base shape in Blender  Consider necessary transforms.  Can do vertex, edge, and face manipulation on polymesh shapes.  Can apply basic transforms to part of a shape.  Can also extrude.  Used to extend a part of a shape.
16. 16. DRAWING AN OBJECT  Can also spin basic shapes: http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Modelling_a_Mu g_using_Spinning_and_Extrusion
17. 17. DRAWING A SHAPE  Blender provides many different modifiers to change the basic structure of how you interact with a shape.  Mirror allows you to mirror modifications across a shape.  Subsurf makes a rough image much smoother and more organic.  Lots of these modifiers  Experimentation is the key
18. 18. MODIFIER - SUBSURF
19. 19. MOLDING A SHAPE  Back to the elephant.  How do we turn a simple shape into what we actually want?  Begin with a sphere  Elephant body  Select appropriate faces on that sphere.  Extrude into legs  Add another sphere  The head  Extrude a trunk  Extrude a tail  The rough work is handled using these kind of processes.
20. 20. EXTRUSION  Extrusion is one of the most powerful tools you have available in blender.  Pick a face, and extend it outwards or inwards.  Used to raise and lower surfaces.  Can be used to create entirely new surfaces.  Used to create shapes where shapes did not previously exist.  For example, in the coffee cup.
21. 21. EXTRUSION
22. 22. TEXTURING  Once you have a basic shape you want to make use of, you can apply various textures to it.  This changes the colour, and how it interacts with light sources.  A base blender scene has three elements.  A light source (by default, the sun)  A camera  A shape
23. 23. TEXTURING  The texturing system in Blender is extremely rich.  You can set how your object interacts with light  You can set the specific kind of rendering to be done  You can choose transparency and type of textures.  Most of these will not be visible except in preview until a scene is rendered.
24. 24. TEXTURES  Importantly, we can also make use of predefined bitmaps for a texture.  We can make use of our own images which get layered onto the shapes we provide.  We’ll see more of this later lectures and labs.  It’s not a simple concept and easier to understand when shown rather than simply described.  Experimentation very important.  Can’t even begin to cover what Blender makes available!
25. 25. SUMMARY  Polymeshes are the graphical representation must used.  We’ll talk about the rest later.  3D Object created by:  Representing geometry  Applying transforms  Applying textures  Rendering