a question on textures and lag

this is really a question on lag rather than on textures, but ... if you are in an area where there is a lot of artwork (images on prims) such as an art gallery, would it cut down on lag if the side of the prim facing the wall were transparent rather than having a visible texture on both sides? hmmm?

Nope, it would infact make it slightly worse due to the fact the transparent texture is different to the one thats being veiwed. So you would be loading 2 taxtures rather than just the one.

It would add to lag. There are three reasons for this:

1. Transparent surfaces need an extra render pass in order to be drawn as transparent. A simple way to think of it is that every transparent surface you see takes twice as long to draw in each frame than does each opaque surface. The more transparency present in your field of view, the lower your frame rate will be.

2. If the transparent texture itself is an extra texture, then you're loading two textures instead of just one.* Remember, transparency is not the absence of texture; it is merely a property, which can be present in a texture or not, just like any color could be present or not. Think of it just like RL. Glass does not cease being a substance, just because you can see through it. Well, a texture does not stop being a texture just because you can see through it either.

3. A texture with transparency will always consume 33% more video memory than a comparably sized texture without transparency. This is because transparent textures have four channels, while opaque textures have just three. See the sticky on video memory at the top of the forum for more information.


What WILL cut down on lag is when you use as few textures as possible. For example, for your painting, put the same texture on all sides of the cube. Then tint all faces black, except the front. This way, you're using only one texture, but the painting appears to be just on one side.




*If you really wanted to, you could use a script to turn the desired faces of the cube transparent, without adding an extra texture. However, all the same rules about rendering would still apply, so the transparency would still slow your frame rate. While you'd be causing less lag than if the transparency were a separate texture, you'd still be causing more than if the whole thing were opaque.

Chosen, thank you for the consistently useful information, I always learn something from your posts!

To clarify, do "blank" textures count as another texture to be rendered?

So, in the example you have given above, would it be better to put the image on all 6 sides and turn it black, or have 5 "blank" sides colored black and put the image only on the 6th side?

I was wondering the same thing as its usually what I do, make all the sides with the blank texture then add the only one i need visible/meaningful.

Yes, the "blank" texture is just a texture, like any other. I can see how its name might be a little misleading, as if applying 'blankness' somehow means removing all texturing. But that's not what it actually means. It simply means you're applying a picture that happens to look like a blank canvas.

Think of it this way. Got any white walls in your house? They've still got paint on them, right, even though they're 'blank'. Whether any particular wall has just one solid color, or has a full-blown mural on it, it's still a wall like any other, and it's still covered in paint. Whatever color(s) the paint happens to be doesn't change anything. Every wall is a painted surface, just like every other.

Likewise, in SL, every surface is textured. A texture could be 'blank', or transparent, or photographic, or full of text, or whatever. But it's still a texture, no matter what. Whatever image it happens to portray, a texture is a texture is a texture.

Or, if you prefer, forget everything I just said, and remember this much. The blank texture is actually a highly detailed photograph of a polar bear blowing his nose in a snow storm.