Interpolate a one texture to another texture

I am trying to achieve transition effect of a one texture another texture while animating mesh with shape key but have no clue how to achieve this. Thanks in advance for help.

To interpolate between textures on the same material / surface, you’ll need a custom shader - that’ll pretty much do just:

vColor = mix(tTexture1, tTexture2, alpha); // NOTE Alpha being a value between 0 and 1, defining the linear interpolation between textures