Texture2D.PackTextures

Parameters

Returns

Rect[] An array of rectangles containing the UV coordinates in the atlas for each input texture, or null if packing fails.

Description

Packs multiple Textures into a texture atlas.

This function will replace the current texture with the atlas made from the supplied textures. The size, format and mipmaps of any of the textures can change after packing.

The resulting texture atlas will be as large as needed to fit all input textures but only up to maximumAtlasSize in each dimension. If the input textures can't all fit into a texture atlas of the desired size then they will be scaled down to fit.

The following conditions will cause the atlas to be created as an uncompressed texture using the TextureFormat.RGBA32 format:

• If not all input textures are compressed.
• If some input textures have mipmaps and others have none.
• If the compressed input textures have mipmaps and padding > 0. This is due to alignment restrictions on the compressed texture formats.

If the texture atlas is compressed and has a padding value greater than zero, the padding value is rounded up to the next multiple of four. This happens because of alignment restrictions on compressed texuture formats.

The atlas packing code only supports the following input texture formats:

• ARGB4444
• ETC
• ETC2
• DXT1
• DXT5
• BC7
• ASTC 4x4

All input textures must have the same compression format or be a mixture of compatible compression formats, otherwise the atlas format falls back to uncompressed. Variants of the same compressed format can be mixed in an atlas, where they stay compressed:

• TextureFormat.DXT1 and TextureFormat::pref:DXT5 result in a TextureFormat.DXT5 atlas.
• TextureFormat.ETC2_RGB, TextureFormat.ETC_RGB4, and TextureFormat.ETC2_RGBA8 result in a TextureFormat.ETC2_RGBA8 atlas.

However, if the input textures mix unrelated formats, such as BC7 with ASTC 4x4 or DXT5, this causes the atlas packing code to fall back to TextureFormat.RGBA32.

If none of the input textures have mipmaps, the atlas also has no mipmaps. Using compressed input textures of varying sizes with mipmaps will limit the resulting atlas mipcount to that of the smallest input texture minus two. This is to ensure each atlas item mip level fills at least one block of compressed data. This can lead to reduced GPU performance as the larger atlas items will be limited in their ability to reduce texture cache pressure by sampling lower resolution mip levels. For optimal performance it is recommended to pack input textures of similar sizes into different atlases.

Take the following compressed atlas example:

• One item is 256x256 with a total of 9 mip levels.
• Another item is 1024x2048 with a total of 12 mip levels.

The resulting compressed atlas will only have 7 mip levels:

• The smallest item (256x256) needs to drop 2 of its mip levels (1x1 and 2x2) to satisfy the compression block size (4x4) alignment requirement.
• The largest item (1024x2048) will need to drop 5 mip levels, with its resulting smallest mip level being 32x32.

Packing both textures into different atlases with similar item sizes, such as one for items with a minimum dimension of 256 and another with a minimum of 1024, will reduce the number of mip levels that are dropped when atlassing.

If makeNoLongerReadable is true then the texture will be marked as no longer readable and memory will be freed after uploading to the GPU. By default makeNoLongerReadable is set to false.

using UnityEngine;

public class Example : MonoBehaviour
{
    // Source textures.
    Texture2D[] atlasTextures;

    // Rectangles for individual atlas textures.
    Rect[] rects;

    void Start()
    {
        // Pack the individual textures into the smallest possible space,
        // while leaving a two pixel gap between their edges.
        Texture2D atlas = new Texture2D(8192, 8192);
        rects = atlas.PackTextures(atlasTextures, 2, 8192);
    }
}