Where We’ve Been… History of Technology in Games ! Processing ! Storage 3D Graphics ! Graphics ! CRT CMPUT 250 ! Vector Graphics Fall 2007 ! Raster Graphics ! Bitmaps Tuesday, October 9 ! Resolution, Colour Depth, Frame Rate ! Early Arcade Games Raster Wins CMPUT 250: Fall 2007 Lecture #10: History 3 … Today ! 2D Graphics ! 3D Graphics ! Camera ! Sprites ! Meshes ! Layers ! Triangles ! Collision Detection ! Models ! Specialization and Generalization ! Culling ! Volume Partitioning ! History of Home Consoles ! Advances in 3D ! Shading and Texturing ! Special Effects CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 3D Graphics Types of Rendering ! This is a very complex subject ! Non Real-Time (e.g., raytracing) ! Video screens are 2D; World is 3D ! Trace paths of beams of light in the world and compute ! Produce a 2D image of a 3D world their colour when they hit the camera’s field of view ! Virtually build our 3D world ! Slow (minutes or hours for one frame) but high quality ! Point a virtual camera at it ! Used in movies like Pixar’s Toy Story, etc. ! How do we describe the objects in the world? ! Sometimes used to pre-render scenes in games Scene ! These images can also be used as a background ! What does our camera do? ! Real-Time Rendering ! Draw image in real-time (quickly enough to animate) ! Lower quality but world can change with player actions CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 The Camera The Camera: Frustum ! A camera is a view of the world ! Volume visible to camera: view frustum ! Occupies a position in 3D space (x,y,z) and points in a direction ! Viewing angle (horizontal and vertical) ! Real cameras also have: ! Focal length ! Lens Distortion ! Focus ! Depth of Field © George Otto, Penn State University CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 The Camera: Styles The Camera: Styles ! Fixed cameras ! Free cameras ! Chase camera (3rd person, follows behind) ! Finite position and direction (Myst, 7th Guest) ! Free-look (1st person, looks wherever you point) ! Fixed position (Myst 3) ! Look-spring (1st or 3rd camera can be moved but ! Fixed direction (some RTS, isometric view) automatically returns to its default when released) ! Rear-view (look behind you) ! Fixed path (rail-shooters like Virtua Cop) ! Droppable (move and then leave it there) ! Fixed path with free direction (rail-shooters like ! Switching from 1st to 3rd or vice versa Panzer Dragoon) CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 The Camera: Friend or Foe? Simple “3D” Tricks ! Obstructions in 3rd person view ! Scaling: making 2D sprites bigger or smaller to simulate moving toward or away ! Where does the chase camera go when you ! Boot Hill (Midway, 1977) back into a wall? ! Isometric view: 2D artistic style showing ! Camera won’t allow the angle you want perspective from a fixed angle ! Camera too slow ! Zaxxon (Sega, 1982) ! These aren’t really rendering ! Camera too erratic or has jerky transitions ! We want a world with real 3D objects (i.e., they occupy ! Camera too automatic or too manual some volume of space… not just an area of the screen) CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 The Scene Polygons ! Need to represent things in the world ! Polygons are 2D objects described by three ! Irrelevant what they look like inside or more points connected by line segments. ! Let’s make “hollow” objects ! They are closed (all line segments ! Here’s the plan: connected) and line segments do not cross ! Objects defined by surfaces (or meshes) each other. ! Surfaces built out of polygons ! A point used to describe a polygon is called ! Polygons built out of triangles a vertex (plural: vertices). ! Triangles defined by their vertices CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Example of Polygons Examples of Non-Polygons Not closed Not line segments Line segments cross CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Triangles Coordinates ! Simplest polygon ! Two dimensional points can be described using 2D coordinates or vertices ! Nice mathematical properties ! Each coordinate is two numbers (x and y), referring to ! Can divide up more complex polygons into horizontal and vertical position triangles (tessellation) ! For our surfaces, we must use 3D coordinates (x, y, z) referring to horizontal, vertical, and depth ! Our polygons (triangles) will be described by 3D coordinates CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Meshes Multiple Meshes ! A collection of triangles for a single ! Figures can be composed of multiple “object” is called a mesh meshes. The pieces (meshes) can separate. ! In the end, a mesh is just a big list of vertex coordinates CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Normal Vectors How to Draw a Scene ! World is built out of many, many triangles ! Recall our objects are hollow and we only ! Place the camera in the world care about the “outside” ! We can calculate what a triangle looks like from the camera’s position ! Which side is the outside? ! But some triangles obscure others (?) ! Normal vectors point out from a triangle’s ! One idea: visible side ! sort triangles by how far away they are ! draw them from furthest to closest ! closer triangles will be drawn over top of further triangles CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Problem Culling ! Too many triangles ! Reduce the number of triangles we need to draw ! Limited number can be drawn per frame ! Culling is the process of eliminating triangles ! Essentially the same problem we had in vector from the list of those we need to draw. graphics and sprite graphics ! Can obviously ignore ! Always need to consider scene complexity ! triangles behind the camera ! Many factors to complexity ! triangles out of the forward field of view up-down and ! Number of potentially visible triangles right-left ! Effects in rendering those triangles ! triangles beyond the camera’s range ! How can we draw complex worlds? ! all this is called frustrum culling ! only consider triangles inside the camera’s frustrum CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 The Camera: Frustum Clipping ! Volume visible to camera: frustum ! Only considering triangles inside the frustum now ! Triangle may only be partially inside ! Cut off part of triangle that is outside ! This process is called clipping © George Otto, Penn State University CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Still have problems… Philosophical Question ! With complex worlds, even computing what triangles are inside the frustum may be too slow! Ever wonder why you can’t just ! Camera’s max depth may cover most of the world blow any and every wall up? ! Need a fast way of deciding what triangles might be visible before we cull ! Let’s break the world up into manageable spaces CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Static vs. Dynamic Objects Volume Partitioning ! Static Objects, e.g., walls, statues, trees ! Use static objects to divide up (partition) ! Precompute (calculate ahead of time) and store the world into separate spaces (volumes) information about the visibility of its triangles ! Use the information to speed up rendering ! Rooms are a natural way to do this ! If most of the world is static… life is good ! We can manually specify the division when ! … but boring we design the levels ! Static objects can still help ! There are more automatic methods, but we start with a portal system. CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Portals Portals ! Divide world into regions connected by portals A A B C ! Camera is limited to triangles in the same B region as it (or adjoining regions) D C ! Allow portals to be open or closed to keep D the number of regions small CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Automated Volume Partitioning ! Automated methods split the world’s volume up into pieces using geometry. ! Examples include ! Binary space partitioning ! Quadtrees ! Octrees ! Many games use a mixture of manual and automatic methods CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Early 3D Early 3D: 2.5D ! Made possible by volume partitioning ! One “floor”: possibly variable height ! 2D graphics (sprites) in a 3D environment ! No rooms above rooms (except by trickery) ! The Games ! History ! Ultima Underworld (Looking Glass, 1992) ! Ultima Underworld allowed a complex environment ! Wolfenstein 3D (id Software, 1992) (angled walls, inclined surfaces) but was slow ! Doom (id Software, 1993) ! Wolfenstein 3D made simplifying assumptions (e.g. all- ! Heretic (Raven Software, 1994) right angles, all floors the same level) and was fast ! Marathon (Bungie, 1994) ! Doom relaxed restrictions (some angled walls, some ! System Shock (Looking Glass, 1994) variable height floors) while keeping the speed ! Duke Nukem 3D (3D Realms, 1996) ! Heretic allowed angling viewpoint up and down CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3 Early 3D: Beyond 2.5D System Shock (Looking Glass, 1994) ! More History: !