Tài liệu 3D Game Programming All in One- P16 docx

Terrains Explained To understand terrains in a game developmentcontext, we need to look at the characteristics ofthe terrain we want to model.. Essentially a ter-rain tile is a collecti

Then choose Image, Rotate, Free Rotate to get the FreeRotate dialog box (see Figure 11.9).

Click the Right button in the Direction frame, and click the

Free button in the Degrees frame Finally, type 1.00 in the text

box next to the Free button, and click OK This will rotate theselected area 1 full degree to the right (see Figure 11.10)

You should have your rotated area with the selection quee still surrounding it Don't touch anything yet—leavethe selection as it is

mar-Now after having explained the Croptool, I'll show you another way tocrop the image that is sometimesmore convenient than using theCrop tool With the rotated area stillselected, choose Image, Crop toSelection and the image will be cropped for you!

You will then end up with an image as shown inFigure 11.11 suitable for use as a texture

Now compare Figure 11.11 with Figure 11.7and you will see the difference

is not to teach you how to draw, so if you want

to learn more, I encourage you to look into ing some lessons

tak-If you are satisfied with your artistic skills, thenyou have another rich avenue for texture gen-eration available to you The techniques used to convert a photograph to a texture can also

be used to convert your hand-made images to textures

Another approach for creating original artwork is to create your images directly in a toollike Paint Shop Pro You can draw freehand using the mouse or a pen tablet

Sources 357

Figure 11.8 Rectangular

Selection tool icon

Figure 11.9 The Free Rotate dialog box.

Figure 11.10 The rotated woodgrain.

Figure 11.11 The cropped woodgrain

image

With tools like Paint Shop Pro you have a wide variety of means for creating textures,including a specific Texture Effects tool in the Effects menu, as shown in Chapter 8 Figure11.12 shows examples of textures created using the built-in features of Paint Shop Pro Iencourage you to explore this tool in depth It can really be a timesaver And you can use

it to create some knockout textures

Scaling Issues

When creating your textures, you will need to payattention to the issue of scale The sizes of the thingswithin an image that is used to make a texture have aparticular relationship to other real-world objects Weare subconsciously aware of many of these relation-ships from our exposure to the world in general andwill notice when the textures are out of proportion tothe items they adorn If it's bad enough the effect cansometimes be similar to the sound of fingernails beingdragged across a chalkboard!

Figure 11.13 shows two stylized houses.The bricks in house A are far too large,while the bricks in house B are moreappropriately sized, yet may still be a bittoo large Yes, there are some uses forstone blocks having proportions such asthose in house A, but they are rarelyused in bungalow-sized or two-storyhomes, as depicted in the figure.The scale issue can pop up anywhere, as youcan see in Figure 11.14 The texture image inthe corrugated metal bridge surface is probablyabout 10 times larger than is appropriate.Sometimes you might need to redo the texture

to match—other times you can adjust how thetexture is applied to the polygons using themodeling tools My rule of thumb is that if thetexture image size is 64 pixels by 64 pixels orsmaller and needs to be made larger, youshould make a new texture at the larger size.The same goes the other way: If the image size

Chapter 11 ■ Structural Material Textures358

Figure 11.14 Scaling error.

Figure 11.13 Scaling bricks.

Figure 11.12 Example textures.

is larger than 64 pixels by 64 pixels and needs to be made smaller, then make a new ture at the smaller size.

tex-Tiling

Many structures have large surfaces with repeating patterns The best way to approachmaking textures for these surfaces is to create one smaller texture that is replicated manytimes across the surface, rather than simply making one large texture

The replication will usually take place in two dimensions It is important to make sure thatthe edges of the texture align properly when they meet Figure 11.15 shows this to goodeffect You can see the obvious horizontal as well as the more subtle artifacts in house Awhere the tiled brick textures don't quite line up In house B, where care was taken toensure that the texture edges matched up correctly, those artifacts aren't visible

However, in house B in Figure 11.15 there

is another obvious artifact of tiling, thistime caused by asymmetric lightingeffects in the texture shading You can seeeach repeated texture tile—its position ismarked by the presence of the darkershaded bricks in a repeated pattern Thiseffect can be quite subtle and difficult todetect in an image viewed in isolation

Figure 11.16 shows the texture used in house B of Figure11.15 Looking at it in isolation, you would be hardpressed to notice the subtly darker shaded bricks

The simplest way to fix up a texture for use as a tiled ture is to copy the left edge, about 5 or 10 pixels wide,mirror the copy horizontally, and then paste the copy onthe right side of the image Do the same for the bottomedge Of course, you can go from top to bottom or right

tex-to left as well The important step is the mirroring

After placing the mirrored edges, spend a little timeblending their inner edges with the interior portions ofthe image

Figure 11.17 shows a stone block texture that is a date for use in a tiling situation

candi-Figure 11.18 shows the texture tiled in a set of four Again,you can see the artifacts caused by the mismatched edges

Tiling 359

Figure 11.15 Tiled brick texture.

Figure 11.17 A stone texture.

Figure 11.16 The brick texture

with asymmetric shading

Figure 11.19 shows theleft edge being copied,mirrored, and placed

on the right

Figure 11.20 shows thesame thing happeningwith the bottom edge.Finally, Figure 11.21shows the tiled result

Texture Types

There are far too manytexture types and class-

es of material ances for me to enu-merate them with anysort of thoroughness.Given that, there is amuch smaller set of tex-ture types that arefound over and over innature and man-madestructures

appear-Most of the following textures are types that are used for buildings, bridges, and otherman-made items in a game world

Irregular

Irregular textures tend to have a general disorder andrandom appearance, like that shown in Figure 11.22 Dirtand grass are examples of irregular textures Quite oftenirregular textures are combined with other, differentirregular textures in order to give a weathered or dam-aged appearance to an area or surface

Chapter 11 ■ Structural Material Textures360

Figure 11.18 Poorly tiled stone

Rough textures, as shown in Figure 11.23, sometimeshave somewhat the same sense about them as irregulartextures They are often used as tiles on a surface like asidewalk or rough concrete walls

Pebbled

Pebbled textures are another example of textures oftenused for paved surfaces and stone walls Tarmacadampavement is an example of a finely pebbled surface whenviewed from a distance

of about 5 or 6 feet

Figure 11.24 shows amore obvious pebbledtexture that could beused for a wall or deco-rative planter

Woodgrain

Figure 11.25 shows awoodgrain texture thathas many highly variantbundles of lines rang-ing from fine to coarse that run roughly parallel to eachother, sometimes interrupted by swirls and knots Somekinds of stone have similar appearances

Metallic textures tend to have a dominant color, with astrong dark shadow that follows the outer contours ofthe metallic object and a bright accent color that runsalong raised surfaces Figure 11.29 shows a texture thatcould be used for a metal tube

Reflective

A reflective texture simulates the effect of a light source

in the scene reflecting strongly off the surface of the tured object Figure 11.30 is such a texture that might bedepicting a bright overhead light reflecting off a window

tex-Plastic

Plastic textures are ilar to metallic textures

sim-in their manner ofshading and highlight-ing Plastic tends tohave more of an oilyappearance to it attimes, so the shadingand highlights are oftenmore sinuous Asshown in Figure 11.31,

Chapter 11 ■ Structural Material Textures362

the highlights tend to be less clearly defined than withmetallic textures, while the light source often appears as

a distinct highlight

Moving Right Along

In this chapter, we examined how to collect images to use

in applying textures to objects that represent real-worldstructures We saw some of the processing techniques that

we may need to use to prepare our images for use as tures, like color matching and cropping

tex-Some of the areas that can be more problematic whenconsidering textures for structures are scaling the images and preparing them to be "tiled"

if the texture will be used in a repeating fashion A texture that can be tiled is one whoseopposite edges can be mated together without producing a noticeable seam

Finally, we explored some of the more common texture patterns and characteristics thatare used in games

In the next chapter, we will look at terrains, which are often used to provide that touch ofrealism in our game worlds Some of the ideas we've covered in this chapter will certain-

ly be useful in the next chapter as well

Moving Right Along 363

Figure 11.31 A plastic texture.

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Terrains

chapter 12

Many games take place exclusively inside buildings or structures, like tunnels

And many other games involve exclusive outdoor game play Then there aresome games that have a mix of each

When your game has an outdoor component, you need to represent the terrain, which in

game terms is the combination of the topography (hilliness, for example) and groundcover (grass, gravel, sand, and so on) The topography is modeled using a 3D model, andthe ground cover is represented by textures

In addition to representing the ground, you also need to represent the sky, if you want to

have interesting outdoor game play Typically, a construct called a skybox is used to

repre-sent all of the sky, from horizon to horizon

Terrains Explained

To understand terrains in a game developmentcontext, we need to look at the characteristics ofthe terrain we want to model These characteris-tics will drive our need for the data that defines theterrain we want to make and therefore will heavi-

ly influence how and where we obtain that data

Terrain Characteristics

A basic unit of terrain is the tile Essentially a

ter-rain tile is a collection of polygons that form a3D model that represents the terrain, as depict-

ed in Figure 12.1

Figure 12.1 An untextured terrain tile.

When we model terrain in a game, there are a number of choices we have to make We

need to decide the level of terrain fidelity we want to achieve Another choice is to figure out the spread of the terrain Finally, we need to decide what sort of freedom the terrain

embodies Table 12.1 lists characteristics and the ramifications of each of these choices

Chapter 12 ■ Terrains366

Table 12.1 Terrain CharacteristicsCharacteristic Description

Fidelity Terrain fidelity measures how accurately the terrain reflects real topography found

somewhere in the world—how realistic it is The realism can be reflected in both the modeling and the textures Modeling fidelity can be described as any of the following:

Realistic: Accurate at 1:1 scale in all dimensions with high-resolution textures

representing the terrain cover.

Semirealistic: Accurately scaled, usually to a smaller size Often the vertical

scale is 1:1 while the horizontal scales are around 1:2 The game World War II Online by Cornered Rat Software has all of Western Europe modeled in this fashion The game uses medium-to-low resolution textures to represent ground cover.

Quasi-Realistic: Not accurately scaled in any dimension, but still attempts to

represent a real location in the world Usually employs high-resolution ground cover textures The scales and textures are chosen to give a sense of the locale that works well in the game environment NovaLogic's Delta Force series takes this approach.

Unrealistic: Everything else! Unrealistic terrain is most commonly used to

specifically enhance game play or the backstory of the game.

Spread Terrain spread is the degree to which areas of the terrain are unique Terrain is created in

units called tiles The spread is related to these tiles in one of three ways:

Infinite: A square terrain region is repeated, or tiled, in all cardinal directions, such

that when the player leaves a region to the west, he enters a new copy of the same terrain tile from the east This continues for as long as the player keeps moving in that one direction.

Finite: The terrain tiles are repeated in all directions, but at some point the

repetition stops.

Untiled: Terrain tiles are not repeated.

Freedom Terrain freedom is the measure of how much the player's in-game movements are

restricted by the terrain Terrain freedom is closely coupled with terrain spread There are really only two degrees of terrain freedom:

Closed: Closed terrain limits player movements in all cardinal directions at some

point With closed terrain, at some point after a player has been moving in a particular direction, he cannot continue that way, either because there is a virtual physical barrier or because the program prevents further movement In any case, the terrain is usually modeled beyond the barrier only as far as the player can see After that—nothing.

Open: Open terrain allows player movement in any direction for as long as the

player wants Some games will warp the player to the "other side" of the world, where he will keep crossing terrain tile copies until he returns to the place he started.

There are practical considerations that direct our terrain design choices Many gameengines simply aren't capable of handling the distances involved in large-scale terrains orthe number of objects required to appropriately populate them Some game genres aren'tsuited to open terrains—the player needs to be confined in order to advance the gamestory as required.

Terrain Data

When you want to create a high-fidelity terrain model of a real place in the world, you aregoing to need to get the data from somewhere If the area in question is small enough, youmay be able to go out and gather the information yourself if you're handy with a theodo-lite (a surveyor's tool) You might be able to glean the necessary information from topo-graphic maps In either case there is a lot of work involved in the data gathering phasealone You will need accurate distance measurements and altitudes, as well as photos ofthe ground cover

But don't despair! There are sources for high-resolution terrain information available onthe Internet If you go to http://edcwww.cr.usgs.gov, the Web portal for the United StatesGeological Survey (USGS; part of the U.S government), you can find a wealth of terraindata

The data is available in several forms, but the standard form is the DEM (Digital Elevation

Model) DEM-formatted data files have the dem file extension Another format in use is

the DTM (Digital Terrain Model), which uses the dtm file extension Finally, a powerful and complex format called SDTS (Spatial Data Transfer Standard) also exists but is not in

wide use outside of scientific niches SDTS files are denoted by the ddf file extension

In any event, the ground cover information is not included in these various model mats, so you'll need to gather that as well Again, the USGS comes in handy with its satel-lite imagery—some of it taken down to a resolution of less than a meter per image pixel

for-DEM files provide elevation information for specific coordinates of places on Earth for-DEM

files can be converted to a format used by game engines called a height map We won't go

into detail about how to use DEM data for your game, but you can use several of theresources listed in the appendixes to locate the data and tools needed

Terrain Modeling

There are basically two approaches that 3D game engines use to model terrain in a 3Dworld In both cases 3D polygon models represent terrains

In the external method we include the terrain as just another object in the game world.

This method offers much freedom of manipulation You can rotate the terrain model,skew it, and otherwise subject it to all manner of indignities All 3D engines support thisapproach While flexible, it is usually an inefficient way to render complex large terrains

Terrain Modeling 367

The second approach is the internal method, where terrain is rendered by special code in the game engine often called a Terrain Manager Using the Terrain Manager approach

allows game engine programmers to apply specific memory and performance tions to the terrain object, because they can discard unnecessary functions that would beavailable to general-purpose objects Because of this, Terrain Manager terrains can some-times be made larger and more complex than those created using other approaches.Most 3D engines, like Torque, that use a Terrain Manager also provide terrain generation,manipulation, and editing tools that we can use to create our own terrains Usuallyimporting height maps is available for terrain generation Some engines, like Torque, havebuilt-in Terrain Editors that allow the game developer to directly manipulate terrain poly-gons, within constraints, to create the desired hills, valleys, mountains, and canyons

optimiza-Height Maps

Figure 12.2 depicts a height map As you can see, it's a grayscale image The 2D nates of the height-map image map directly to surface coordinates in the game world Thebrightness off each of the pixels in the image represents the altitude at that pixel's loca-tion—the brighter the pixel, the higher the elevation Usually we use an 8-bit per pixel for-mat, which means that 256 discrete elevations can be represented

coordi-The concept is an elegant one and not difficult to grasp If you are familiar with viewingtopographic charts and maps, you'll find that height maps have a familiar flavor to them,even though the contour lines are missing One of the deficiencies of height maps is the res-olution (as you can see in Figure 12.2) To represent a geographic locale that is 1 kilometersquare, a height map that represents 1 square meter as a pixel needs 1,000 pixels per side, for

a total of 1 million pixels—big, but not too large If I want to increase the terrain area tocover 16 square kilometers (4 meters per side), then I need to store 16 million pixels At 8

bits per pixel, that equals about 16MB of data If wewant to model the terrain for an area that is 10 kilo-meters per side, we are looking at 100MB of storage!

We can, of course, reduce the terrain resolution—let's say, have a pixel equal 4 square meters in thegame world This would chop those 100MB back to6.25MB However, that gain is offset by the fact thatour terrain will now be blockier and less realistic.Figure 12.3 shows a terrain model generated fromthe height map shown in Figure 12.2 In this caseMilkShape was used to import the height map andcreate the terrain object

Chapter 12 ■ Terrains368

Figure 12.2 A terrain height map.

Terrain Cover

In the simplest sense, terrain cover refers to all the

stuff that you find on the ground, including:

We represent the terrain cover with textures Our options for creating these textures aremuch like those we considered when we created textures for structures in Chapter 11—

and the factors that dictate which way to choose are also similar It boils down to the rain characteristics in the game that matter to you

ter-We can also mix terrain cover textures in adjacent areas to portray a particular locale It's agood idea to develop your own library of generic terrain cover for use in various situations

Figure 12.4 illustrates some of the possible varieties of terrain cover From left to right inthe top row you can see grass, sand, and an intermixed sand and grass texture In the bot-tom row from left to right are dirt, a muddy track, and eroded wet sand

Tiling

Unless you are going to create specific terraincover textures for every square inch of terrain,you will end up tiling your terrain cover atsome point All the issues brought up withtiling in other contexts apply here, such asmatching texture edges to get seamless transi-tions and ensuring lighting in the textures isboth appropriate and uniform Additionally,

you should ensure that there are no patterns or marks in the texture that will stand outtoo much when the texture is repeated.

In Figure 12.5 you can see a repeating light pattern that tends to overpower the otherwise

pleasing and pastoral scene (Okay, okay, it would be pastoral if a storm wasn't brewing

beyond the, um…Mountains of Evil in the distance But besides that…)The culprit in this case is the grass texture used, which is shown in Figure 12.6

Notice the area of lighter grass, which is quite noticeably different from the rest of theimage When repeated over and over across large swaths of terrain, that feature detractsfrom the intended overall effect We can enhance the image to minimize the problem, per-haps with something like that shown in Figure 12.7

The result is dramatic and the difference is quite obvious, as you can see in Figure 12.8.Now, I confess that the texture could be better, but you have to admit that it is light-years

ahead of the first version,shown in Figures 12.5 and 12.6

Creating Terrains

Okay, enough talk Time forsome action—let's create someterrain We'll use the TorqueEngine and its internal TerrainManager to create the terrain,and we'll employ the height-map method using the in-game Terrain Editor There isanother method, direct manip-ulation, that we'll use later inChapter 18

The Height-Map Method

For this section, you willneed to fire up Paint ShopPro You should be fairlyfamiliar with the basics, so Iwon't hold your hand toomuch with respect to PSPoperations

Chapter 12 ■ Terrains370

Figure 12.5 A terrain with tiling artifacts.

Figure 12.6 A texture with

an undesirable feature

Figure 12.7 A texture

without the undesirable feature

One WU in Torque is equal toone unit in most third-partymap editors A WU is equiva-lent to one scaled inch.

1 Start with a drawing ofthe contours to createthe height-map image

If you have a source forcolored contour drawings for a section of land drawn at full scale (1:1), such as shown

in Figure 12.9, get one that suits your needs If not, you can use the images shownhere, but in their colored format, which you will find

at C:\3DGPAi1\RESOURCES\CH12 Each image hasthe same name as the figure number used here

2 Clip out the portion you want and save it as a PNGimage, as shown in Figure 12.10

3 Now you need to do a little noodling over scale andunit numbers

In Torque each terrain square is made of two terraintriangles sized at 256 WU by 256 WU; as mentionedearlier, the default squareSize property in a Torquemission file equals 8 by default The terrain has

256 of these squares per side for a total of 65,536world units (inches) per side

1 mile=1,609 meters 1,664.6177 meters ⫼1,609 meters per mile=1.034 miles

Creating Terrains 371

Figure 12.8 The terrain with improved tiled texture.

Figure 12.10 Cropped and

resized contour map

Figure 12.9 Contour map.