Should we avoid a padding of transparent pixels around an image when creating Assets to be used in 3D Space?

Question

Assuming we are creating Assets to be used on iOS in order to create textures that are then mapped to the surface of Quads in 3D Space, is below recommendation and its reasoning appropriate?

Try to avoid unnecessary* transparent pixels whilst ensuring a Power of 2 texture size.

Since the texture will occupy the same amount of RAM whether it has its content spread across its entire surface or not, try to use as much of the available surface for the content as possible. This will improve visual quality when downsizing the texture (e.g. to generate Mipmaps).

Example (for illustrative purposes, transparency is represented by a Gray color):

*e.g.: a padding of transparent pixels around an image could be considered unnecessary if the texture will be resized anyway.

Answer 1

The reasoning is correct, as long as you take into account usage of the texture.

1. When texture is used on a 3D model (or a 2D with transformation), then having extra resolution/details for the same performance "price" is almost always better (but see n.3).

2. When texture is used in 2D and does not intended to be resized, then you might want to have it in the exact scale you are going to display it. Otherwise you end up with "larger-than-needed" texture being scaled down, which provides poorer quality (slightly blurry or jaggy, depending on resize method) than when texture is drawn to be rendered pixel-to-pixel perfectly.

3. Much alike n.2, sometimes your artistic style will call for specific texture sizes (think pixel-art games). E.g. ship's texture has to be exactly 176x221 pixels to match the scale of 1px thin and 3px thick lines. In that case you will have to sacrifice performance/memory for aesthetics.