1. CSE 381 – Advanced Game Programming Terrain Management
state.edu/~somasund/GRAPHICS/TeapotPhongOUT.jpg 1

2. Think of it as a textured blanket

3. 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

4. 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?

5. 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

6. 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

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

8. 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

9. 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

10. 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)

11. 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

12. 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.

13. 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

14. 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

15. 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

16. 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

17. 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)

18. 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

19. 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

20. 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?

21. Skies Add ambiance Add realism Add value Note: Inside or outside game?
Different genres use different approaches
rpg vs. fps
Inside or outside game? 21

22. Approaches
Skyplanes
Skyboxes
Skydomes
Cloud Generation & rendering

23. For all approaches Render in sky space Huh?
Render first, with depth buffer off
Use geometry that fits sky textures
minimize interpolation
this means sky geometry is much smaller than other objects

24. Skyplanes Simplest to model and texture
Does not completely enclose camera
Disadvantage:
End of plane is noticible
Doesn’t cover horizon
Should only be used when mountains or other objects fills gaps

25. Simplest Skyplane Approach
Use 2 triangles
put them right over the camera
Ex: 1 y-unit above camera at all times
Move sky with camera
Map sky texture onto geometry
again, minimize interpolation
No minification or magnification
What determines this? How you:
size it
texture it
position it

26. Alternative: curved plane
Shaped like a parachute
Considerations:
Resolution (number of vertex rows/columns)
Radius
Height of peak
Repetitions of texture

27. Creating the Geometry How can we create vertices that are:
evenly spaced
part of mesh centered over 0,0
in x&z range -planeSize/2 through planeSize/2
Plane size = √((2*radius)2/2)
Using Pythagorean theorem, in loop, calculate distance to determining y values

28. Rendering Skyplanes Disable:
lighting
fog
depth testing
To blend clouds with sky, enable OpenGL blending

29. Sky Fading
Note that the sky fades on the horizon, it doesn’t just get cut off
How can we add this effect?
For skyplane, add alpha value to all vertices:
those nearest center (0, ?, 0) fully opaque,
gradually + and – from center more transparent
use a linear, or better yet, exponential function

30. Clouds with Volume How do we add 3Dish clouds? Use Layers of them
same and different textures
blend them

31. Skyboxes Most common sky rendering technique Fully encloses camera
Inexpensive
Again, enclose camera in small box
How does it work?
render distant scenery onto inside or cube

32. Skybox Atlas 32

33. Traditional Approach Render ordinary textured cube
Align with the world axis
Centered around camera
Render it first
Disable necessary features as before
Size of box can be small
it should fit the textures
make sure it’s in the frustum

34. Skybox Rendering Steps
Clear the depth buffer
Disable depth test
Disable depth writes
Disable fog and lighting
Render the box
Enable depth test and writes
Enable lighting and fog
Draw the rest of the scene

35. Skybox Edges Boxes have seams We don’t want those to show up
Why would they?
mag/minification
may sample nearby pixels
border may be nearby
results in poor interpolation
Alternative, use texture coordinates that don’t start at edge, but one pixel off edge
or employ GL_CLAMP_TO_EDGE
ignores edge texels in interpolation

36. Does the skybox move? Not relative to the camera
Camera can rotate, of course
Skybox goes where ever the camera is
Assumption is skybox art is of things very far away

37. Generating Skybox Art Common to make a large, continuous texture
to wrap around sides, for example
Break it up for texturing
Good tools exist:
Skypaint by Gavin Bell
paint seamless, panoramic 360 deg. Images
Terragen by Planetside
generate sky boxes and terrain

38. Skybox Layering Can provide more beautiful experiences
Example: 3 layers
Outer layer for static background (e.g. stars)
Middle layer for dynamic stuff (e.g. clouds)
Inner layer for much closer stuff (e.g. mountains)
Middle layer may use texture animation
Means moving textures across a geometry
How?
Gradually adjusting texture coordinates

39. Textures vs. Colors
Note that skies transition from horizon colors to sunset colors and make a smooth transition
Colored Vertex rendering can do this easily
more easily than texturing
Option, use colors for outer layer, textures for inner layers

40. For multi-layered approach
Draw outer skybox layers
Disable depth writing
Draw skyplane
Enable depth writing
Draw inner skybox layers

41. Skydomes For even better sky rendering Good for night-day transitions
Good for advanced effects
Uses one texture (for back layer)
Provides better terrain sky transitions 41

42. Generating Vertices Use spherical equations
Polar coordinates
calculate evenly spaced points on globe
For more on Skydomes and advanced sky rendering, see the end of Chapter 9