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

Then choose Image, Rotate, Free Rotate to get the Free

Rotate 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 the

selected area 1 full degree to the right (see Figure 11.10).

You should have your rotated area with the selection mar￾quee still surrounding it. Don't touch anything yet—leave

the selection as it is.

Now after having explained the Crop

tool, I'll show you another way to

crop the image that is sometimes

more convenient than using the

Crop tool. With the rotated area still

selected, choose Image, Crop to

Selection and the image will be cropped for you!

You will then end up with an image as shown in

Figure 11.11 suitable for use as a texture.

Now compare Figure 11.11 with Figure 11.7

and you will see the difference.

Original Artwork

The other approach to creating textures is to

use original artwork. Some people believe this

is not a real option for them, because they

think they can't draw or paint to save their

lives. I tend to feel that everyone can learn the

techniques required. My intent here, however,

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

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

If you are satisfied with your artistic skills, then

you 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 tool

like 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.

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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. Figure

11.12 shows examples of textures created using the built-in features of Paint Shop Pro. I

encourage 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 pay

attention to the issue of scale. The sizes of the things

within an image that is used to make a texture have a

particular relationship to other real-world objects. We

are subconsciously aware of many of these relation￾ships from our exposure to the world in general and

will notice when the textures are out of proportion to

the items they adorn. If it's bad enough the effect can

sometimes be similar to the sound of fingernails being

dragged 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 more

appropriately sized, yet may still be a bit

too large. Yes, there are some uses for

stone blocks having proportions such as

those in house A, but they are rarely

used in bungalow-sized or two-story

homes, as depicted in the figure.

The scale issue can pop up anywhere, as you

can see in Figure 11.14. The texture image in

the corrugated metal bridge surface is probably

about 10 times larger than is appropriate.

Sometimes you might need to redo the texture

to match—other times you can adjust how the

texture is applied to the polygons using the

modeling tools. My rule of thumb is that if the

texture image size is 64 pixels by 64 pixels or

smaller and needs to be made larger, you

should make a new texture at the larger size.

The same goes the other way: If the image size

358 Chapter 11 ■ Structural Material Textures

Figure 11.14 Scaling error.

Figure 11.13 Scaling bricks.

Figure 11.12 Example textures.

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

Tiling

Many structures have large surfaces with repeating patterns. The best way to approach

making textures for these surfaces is to create one smaller texture that is replicated many

times 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 that

the edges of the texture align properly when they meet. Figure 11.15 shows this to good

effect. You can see the obvious horizontal as well as the more subtle artifacts in house A

where the tiled brick textures don't quite line up. In house B, where care was taken to

ensure 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, this

time caused by asymmetric lighting

effects in the texture shading. You can see

each repeated texture tile—its position is

marked by the presence of the darker

shaded bricks in a repeated pattern. This

effect can be quite subtle and difficult to

detect in an image viewed in isolation.

Figure 11.16 shows the texture used in house B of Figure

11.15. Looking at it in isolation, you would be hard

pressed to notice the subtly darker shaded bricks.

The simplest way to fix up a texture for use as a tiled tex￾ture is to copy the left edge, about 5 or 10 pixels wide,

mirror the copy horizontally, and then paste the copy on

the right side of the image. Do the same for the bottom

edge. Of course, you can go from top to bottom or right

to left as well. The important step is the mirroring.

After placing the mirrored edges, spend a little time

blending their inner edges with the interior portions of

the image.

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

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.

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