Blend modes should do what you are trying to do. I'm not getting much from your description. Just put your 'texture' layer above the layer you want to add a texture to and pick a blend mode.
The other option is to use the texturize effect. This will make things look more like texturing in a 3D app.
Thanks Rick, sorry if I wasn't clearer but I'm basically looking for an effect that does what your saying so there's no need for multiple layers. The texturize effect is nice but not what I'm after.
You are asking the impossible from After Effects. If you want to apply data from an image to another layer you need two layers in the composition. Both do not need to be visible. Your thought process is flawed. How can you use information from two different sources if they are not both included in the system that makes the calculations. It like asking to solve the equation X + = Z. You can't solve the problem unless you include Y.
How come you are able to do it ( sort of ) with some channel effects like cc calculations? They do everything I'm asking for except the overlayed image does not move when the layer it's applied to moves.
The texturize effect is also a few options away from achieving what I'm asking for as well.
You said you wanted to do it with one layer. If there's only one layer in your composition there's only one source. Even with texturize or any of the other channel operations you need a reference layer. That becomes two layers.
Your original question was adding a texture to a layer from an image. So you need the layer, the texture, and some kind of operation performed by a blend mode or an effect. That is two layers.
You gave a little hint in your last reply that you want the texture to move with layer. That just involves applying the same position animation to both layers through the use of pre-composing, parenting, expressions, or motion tracking. If I knew exactly what you were trying to do I can give you a much better idea of how to do it. I don't know anything at all about the original layer that you want to apply the texture too.