Perform the Working with different types of textures recipe given in this chapter, so that we've got a basic AndEngine project set up with BitmapTextureAtlas or BuildableBitmapTextureAtlas loading in place.

In order to modify a texture atlas' option and/or format, we need to add a parameter or two to the BitmapTextureAtlas constructor depending on whether we'd like to define either the options, format, or both. See the following code for modifying both, texture format and texture options:

BitmapTextureAtlas mBitmapTextureAtlas = new BitmapTextureAtlas(mEngine.getTextureManager(), 1024, 1024, BitmapTextureFormat.RGB_565, TextureOptions.BILINEAR);

From here on, all texture regions placed on this specific texture atlas will have the defined texture format and option applied to it.

AndEngine allows us to apply texture options and formats to our texture atlases. The various combination of options and formats applied to a texture atlas will affect the overall quality and performance impact that sprites have on our game. Of course, that is if the mentioned sprites are using ITextureRegion objects, which are related to the modified BitmapTextureAtlas atlas.

The base texture options available in AndEngine are as follows:

Take a look at the following figure to see a comparison between bilinear filtering and nearest filtering:

These two images are rendered in the highest bitmap format. The difference between nearest and bilinear filtering is very clear in this case. In the left-hand side of the image, the bilinear star has almost no jagged edges and the colors are very smooth. On the right-hand side, we've got a star rendered with the nearest filtering. The quality level suffers as jagged edges are more apparent and if observed closely, the colors aren't as smooth.

The following are a few additional texture options:

Repeating: The repeating texture option allows the sprite to "repeat" the texture assuming that the ITextureRegion object's width and height has been exceeded by the size of the sprite. In most games, the terrain is usually generated by creating a repeating texture and stretching the size of the sprite, rather than creating many separate sprites to cover the ground.

Let's take a look at how to create a repeating texture:

    /* Create our repeating texture. Repeating textures require width/height which are a power of two */
    BuildableBitmapTextureAtlas texture = new BuildableBitmapTextureAtlas(engine.getTextureManager(), 32, 32, TextureOptions.REPEATING_BILINEAR);
    
    // Create our texture region - nothing new here
    mSquareTextureRegion = BitmapTextureAtlasTextureRegionFactory.createFromAsset(texture, context, "square.png");

    try {
      // Repeating textures should not have padding
      texture.build(new BlackPawnTextureAtlasBuilder<IBitmapTextureAtlasSource, BitmapTextureAtlas>(0, 0, 0));
      texture.load();

    } catch (TextureAtlasBuilderException e) {
      Debug.e(e);
    }

The previous code is based on a square image which is 32 x 32 pixels in dimension. Two things to keep in mind when creating repeating textures are as follows:

Next, we have to create a sprite which uses this repeated texture:

/* Increase the texture region's size, allowing repeating textures to stretch up to 800x480 */
ResourceManager.getInstance().mSquareTextureRegion.setTextureSize(800, 480);
// Create a sprite which stretches across the full screen
Sprite sprite = new Sprite(0, 0, 800, 480, ResourceManager.getInstance().mSquareTextureRegion, mEngine.getVertexBufferObjectManager());

What we're doing here is increasing the texture region's size to 800 x 480 pixels in dimension. This doesn't alter the size of the image while the repeating option is applied to a texture, rather it allows the image to be repeated up to 800 x 480 pixels. This means that if we create a sprite and supply the repeating texture, we can scale the sprite up to 800 x 480 pixels in dimension, while still displaying a repeat effect. However, if the sprite exceeds the width or height dimensions of the texture region, no texture will be applied to the exceeding area.

Here's the outcome taken from a device screenshot:

Pre-multiply alpha: Lastly, we have the option to add the pre-multiply alpha texture option to our textures. What this option does is multiply each of the RGB values by the specified alpha channel and then apply the alpha channel in the end. The main purpose of this option is to allow us to modify the opacity of the colors without loss of color. Keep in mind, modifying the alpha value of a sprite directly may introduce unwanted effects when using pre-multiplied alpha values. Sprites will likely not appear fully transparent when this option is applied to sprites with an alpha value of 0.

When applying texture options to our texture atlases, we can choose either nearest or bilinear texture filtering options. On top of these texture filtering options, we can include either the repeating option, the pre-multiply alpha option, or even both.

Aside from texture options, AndEngine also allows us to set the texture format of each of our texture atlases. Texture formats, similar to texture options, are often decided upon depending on its purpose. The format of a texture can greatly affect both the performance and quality of an image even more noticeably than the texture options. Texture formats allow us to choose the available color ranges of the RGB values in a texture atlas. Depending on the texture format being used, we may also allow or disallow a sprite from having any alpha value which affects the transparency of the textures.

The texture format naming conventions are not very complicated. All formats have a name similar to RGBA_8888, where the left-hand side of the underscore refers to the color or alpha channels available to the texture. The right-hand side of the underscore refers to the bits available to each of the color channels.