CSE 381 – Advanced Game Programming Terrain Badlands, South Dakota

Think of it as a textured blanket

Obviously a rendering challenge Also a collision detection challenge Terrain Obviously a rendering challenge Also a collision detection challenge Requires a huge amount of data for outside game environments Usually pre-lit – what does this mean? Typically integrated with: sky water sun

Terrain Characteristics fidelity how realistic is it? for model & textures spread degree to which areas of the terrain are unique freedom how much are the player’s movements restricted by the terrain? Want real earth terrain data? http://edcwww.cr.usgs.gov

Some game engines have terrain managers Terrain Modeling Some game engines have terrain managers with their own GUI terrain generation tools with their own rendering optimizations Terrain building as models can also be positioned, rotated, etc. as one

Texturing provides this Typical textures: Terrain Cover Texturing provides this Typical textures: grass, flowers, dirt, pebbles, rocks, moss, sand, stone, etc. Most engines support terrain texture blending What’s that? good for transition areas at borders of differing terrain

When making Terrain Textures avoid making distinctive marks Why? avoid making textures with patterns Remember, these will be repeated over an area

How do you think terrain data is stored? Height maps What’s that? a 2D image that stores topographical info for a square map region different shades of gray represent different elevations brightness of a pixel denotes its elevation

Each pixel represents an area’s elevation More on height maps Each pixel represents an area’s elevation ex: 1 pixel is a square meter black may be the base elevation pure white may be the other extreme values in between are scaled Ex: 8 bits per pixel means 256 possible elevations

Each pixel represents a tile (square of terrain) For each tile Using Height Maps Terrain generator reads a height map file and creates the appropriate geometry How? Each pixel represents a tile (square of terrain) For each tile a vertex is generated at appropriate elevation two triangles are generated connecting new vertex to bordering vertices Some generators will add more vertices Why? Interpolation (more on this later)

Terrain Units WU – world units Example: refers to measurement scale for a game world basic WU is one inch Example: level tile is 10 X 10 units (meters or otherwise) 100 tiles X 100 tiles level is 1000 X 1000 NOTE: each tile may have many triangles again, depending on interpolation

Think of as its own level object Has a position, scale, rotation Water Think of as its own level object Has a position, scale, rotation Typically specified using a single rectangle can fit into non rectangular terrain contours For camera out of water: typically water drawn using multiple textures one for shallows, one for deep can be blended via depth gradient effects then applied E.g., specular highlights For camera under water: other effects like fog, viscosity, waves, etc.

Terrain Rendering What do we need to know? how to store the data how to load it how to render it how to detect collisions with it. Why? Nothing should go below the terrain

Height Maps Revisited Height maps are images When a level is loaded, how might we store terrain data such that it can be efficiently: rendered used in collision detection calculations

2 Terrain Management Options Static Option - Load height map into a mesh (or meshes) and treat terrain as any other mesh easy to implement typically divided into clumps Dynamic Option - Load height map data into data structure, each frame, use dynamically changing mesh based on location of frustum that’s a bit trickier

Clumps What’s a clump? What’s the benefit of managing clumps? Why? a chunk of terrain subset of a level’s full terrain What’s the benefit of managing clumps? more efficient rendering/management of terrain Why? problem reduction

Clump Construction Example Suppose we are loading a 256 x 256 height map Construct terrain as 16 x 16 clumps How many clumps is that? 256 How many vertices per height map pixels? depends on interpolation (more on this in a moment)

How do we use the clumps? Each frame, select only the visible clumps for rendering How do we do that? frustum culling is one way but there’s a simpler way clumps are cells in the 2D grid in what cell is the camera? render that clump in which direction is the look at vector? render those clumps know the max clump distance that can be viewed

Dynamic Terrain Generation Height map is a 2D grid At start of level: build a recyclable mesh to store dynamic terrain Each frame: determine where on the grid the camera is fill dynamic terrain with visible portions of grid

What’s the point of interpolation? Rounding terrain How? add more vertices to the grid Simple algorithm add 2 between each pair of vertices what height? make them closer to nearest existing vertex than 1/3 of height difference. Why?