Panda3D Manual: Choosing a Texture Size
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Standard Texture Sizes Most graphics hardware requires that your texture images always be a size that is a power of two in each dimension. That means you can use any of the following choices for a texture size: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, or so on (but unless you have a really high-end card, you'll probably need to stop there). The textures don't usually have to be square: they don't have to have the same size in both dimensions. But each dimension does usually have to be a power of two. So 64 × 128 is all right, for instance, or 512 × 32, or 256 × 256. But you can't make a texture image that is 200 × 200 pixels, since 200 isn't a power of two. By default, Panda3D will automatically rescale any texture image down to the nearest smaller power of two when you read it from disk, so you usually don't have to think about this--but your application will load faster if you scale your textures properly in the first place. If you would like Panda3D to rescale your images up to the next larger power of two instead of down to the next smaller power of two, use:
    textures-power-2 up
In your config file. The default is:
    textures-power-2 down
Note that the size you choose for the texture image has nothing to do with the size or shape of the texture image onscreen--that's controlled by the size and shape of the polygon you apply it to. Making a texture image larger won't make it make it appear larger onscreen, but it will tend to make it crisper and more detailed. Similarly, making a texture smaller will tend to make it fuzzier. Padded Textures Sometimes, you need to load data into a texture every frame. The most common example is when you're playing a movie. Let's say, for example, that the movie is encoded at 640x480 at 30fps. Neither of those dimensions is a power-of-two. It would theoretically be possible for Panda3D to rescale the image to 512x512, but it would have to do it 30 times per second, which is too expensive to be practical. Instead, panda pads the data. Panda creates a 1024x512 texture, which is the smallest power-of-two size that can hold a 640x480 movie. It sticks the 640x480 movie into the lower-left corner of the texture. Then, it adds a black border to the right edge and top edge of the movie, padding it out to 1024x512. From that point forward, it's just a texture with a movie in the lower-left corner, and black bars on the upper and right sides. However, if you use UV coordinates carefully, you can cause just the movie to be displayed. To do this, you need to know how big those black bars are:
    padx = texture.getPadXSize()
    pady = texture.getPadYSize()
Panda3D only uses padded textures in a few very special cases: 1. When playing a non-power-of-two movie. 2. When using render-to-texture, and a non-power-of-two buffer. Nonstandard Texture Sizes Some newer graphics cards can render textures that are not a power of two. This is generally not very useful for loading art from disk: after all, game art is usually created in power-of-two sizes no matter what. However, it is useful to avoid wasteful movie padding of the kind described above. If you have one of these cards and you want to enable the use of non-power-of-two textures, you can put the following line in your Config.prc:
    textures-power-2 none
You can also attempt to have panda detect your video card's capabilities automatically, using this command:
    textures-auto-power-2 #t
If this variable is true, then panda will wait until you open a window, and then ask the window's driver if the driver supports non-power-of-two textures. If so, then the config variable `textures_power_2` will automatically be adjusted. In this way, you can configure Panda3D to use non-power-of-two textures if they are available. Caution: there is a potential pitfall when using `textures-auto-power-2`. If you open a window that supports non-power-of-two textures, panda will switch into `textures-power-2 none` mode. If you then open a second window using a different video card which doesn't support non-power-of-two textures, then panda will have no choice but to print an error message. Note that some cards appear to be able to render non-power-of-two textures, but the driver is really just scaling the textures at load time. With cards like these, you're better off letting Panda do the scaling, or dynamic textures may render very slowly.
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