Graphics.CopyTexture

Parameters

Description

Copies pixel data from one texture to another.

This method copies pixel data from one texture to another on the GPU. If you set Texture.isReadable to true for both src and dst textures, the method also copies pixel data on the CPU.

If you set Texture.isReadable to false, CopyTexture is one of the fastest ways to copy a texture. But to use CopyTexture, the following must be the same in both the source and destination texture areas:

• Format. You can also use two compatible formats - for example, TextureFormat.ARGB32 and RenderTextureFormat.ARGB32.
• Size.
• RenderTexture.antiAliasing values, if the textures are render textures.

You might be able to copy between incompatible formats depending on your graphics API. For example, on some APIs you can copy between formats with the same bit width.

Depending on your graphics API, you might not be able to copy between different types of textures. For more information on compatibility, see SystemInfo.copyTextureSupport and CopyTextureSupport.

If src is a depth-only render texture, you must copy the whole texture, not part of it. A depth-only render texture has its color buffer set to a color format of None and its depth buffer set to a valid RenderTexture.depthStencilFormat.

When you use QualitySettings.globalTextureMipmapLimit, Texture2D.mipmapLimitGroup and Texture2D.ignoreMipmapLimit, textures can have a variety of mipmap limit settings. This means you may not be able to copy from one mipmap level to another, because for example the source texture is limited to half resolution and the destination texture is limited to quarter resolution.

If you need to copy a mip between textures with different mipmap limit settings, use the region-based overload. This overload adjusts the source rectangle based on the source texture's mipmap limit settings, and the destination offset based on the destination's mipmap limit settings. For example, copying a 128x128 area from position 16,16 to position 32,32 results in a variety of behaviors based on the global texture mipmap limit, the source texture type, and the destination texture type:

• When the global texture mipmap limit is 0, and both textures are subject to it, Unity performs all copies as expected.
• When the global texture mipmap limit is 2, and both textures are subject to it, Unity adjusts the source rectangle to 32x32 and its offset to 4,4, then changes the destination offset to 8x8. Unity then performs all copies as expected and ignores all mipmap limit settings.
• When the global texture mipmap limit is 2, the source is a texture subject to it, and the destination is an array texture, Unity adjusts the source rectangle to 32x32 and its offset to 4,4, but doesn't change the destination offset, which remains 32x32, because array textures are never subject to mipmap limit settings.

The following sample shows how you can copy to or from a Texture2DArray, when Texture2Ds have mipmap limits:

using UnityEngine;

public class CopyTextureSample : MonoBehaviour
{
    // Sample to copy all available mips: inTex -> outArray (no mipmap limits) -> outTex
    [SerializeField] Texture2D inTex;
    [SerializeField] Texture2DArray outArray;
    [SerializeField] Texture2D outTex;
    [SerializeField] bool considerMipmapLimits;

    void Start()
    {
        int width = inTex.width;
        int height = inTex.width;
        
        outArray = new Texture2DArray(width, height, 1, inTex.format, true);
        outTex = new Texture2D(width, height, inTex.format, true);

        if (!considerMipmapLimits)
        {
            // Texture2D -> Texture2DArray
            // Global Mipmap Limit: "1: Half Resolution" => copies into mips that are now too large; will copy each mip of inTex into a quarter of outArray
            for (int mip = 0; mip < inTex.mipmapCount; ++mip)
            {
                int copyWidth = width >> mip;
                int copyHeight = height >> mip;
                Graphics.CopyTexture(inTex, 0, mip, 0, 0, copyWidth, copyHeight, outArray, 0, mip, 0, 0);
            }

            // Texture2DArray -> Texture2D 
            // Global Mipmap Limit: "1: Half Resolution" => errors, since we try to copy into mips that are now too small
            for (int mip = 0; mip < outArray.mipmapCount; ++mip)
            {
                int copyWidth = width >> mip;
                int copyHeight = height >> mip;
                Graphics.CopyTexture(outArray, 0, mip, 0, 0, copyWidth, copyHeight, outTex, 0, mip, 0, 0);
            }
        }
        else // considering mipmap limits
        {
            int globalMipmapLimit = QualitySettings.globalTextureMipmapLimit;
            
            // Texture2D -> Texture2DArray
            // Global Mipmap Limit: "1: Half Resolution" => mip0 of outArray is not written to, other mips copy as expected
            //  (ALTERNATIVE: if outArray creation already considered globalMipmapLimit for its dimensions,
            //   the CopyTexture call can ignore globalMipmapLimit since the mips will line up again) 
            for (int mip = 0; mip < inTex.mipmapCount - globalMipmapLimit; ++mip)
            {
                int copyWidth = width >> mip;
                int copyHeight = height >> mip;
                int srcMip = mip;
                int dstMip = mip + globalMipmapLimit;
                Graphics.CopyTexture(inTex, 0, srcMip, 0, 0, copyWidth, copyHeight, outArray, 0, dstMip, 0, 0);
            }

            // Texture2DArray -> Texture2D 
            // Global Mipmap Limit: "1: Half Resolution" => mip0 of outArray is not copied (but outTex does not upload it to GPU anyway)
            for (int mip = globalMipmapLimit; mip < outArray.mipmapCount; ++mip)
            {
                int copyWidth = width >> mip;
                int copyHeight = height >> mip;
                int srcMip = mip;
                int dstMip = mip - globalMipmapLimit;
                Graphics.CopyTexture(outArray, 0, srcMip, 0, 0, copyWidth, copyHeight, outTex, 0, dstMip, 0, 0);
            }
        }
    }
}

Mipmap level arguments always refer to a texture's currently loaded mipmap levels. For example, mip 1 of a 256x256 texture subject to a global texture mipmap limit of 0 refers to a 128x128 mip. However, for that same texture if the global texture mipmap limit is set to 1, mip 1 refers to a 64x64 mip. If we were to set the global texture mipmap limit to 2, mip 1 of that same texture would refer to a 32x32 mip, and so on...

This means when you use CopyTexture you do not need to take mipmap limit settings into account in your calls in most cases. However, if the source and destination's mipmap limit settings differ, you need to adjust for those settings. Keep in mind that non-2D texture types are always uploaded to the GPU at full resolution as they do not support mipmap limit settings of any sort.

Compressed texture formats add some restrictions to the CopyTexture with a region variant. For example, PVRTC formats are not supported since they are not block-based (for these formats you can only copy whole texture or whole mip level). For block-based formats (e.g. DXT, BCn, ETC), the region size and coordinates must be a multiple of compression block size (4 pixels for DXT).

Even if you set Texture.isReadable to true, this method doesn't copy pixel data on the CPU if you copy only a region of a compressed texture.

Don't use an Apply method such as Texture2D.Apply after CopyTexture, because you might copy old or undefined CPU texture data to the GPU.

Additional resources: CopyTextureSupport.