Combining multiple UVs and exporting to UDK
polycounter lvl 9
I'm confused about unwrapping multiple components to a scene and combining those unwraps into one UV square. Also, I'm not understanding the idea of saving texture memory by sharing texture space by combining textures sheets into one. Here are some examples for me to better elaborate what I mean:
Let's say you have a few props and a building such as this
and everything is unwrapped into one UV space like this
If I wanted to export just the ladder and drainage pipe to UDK, how does it affect any texturing I've done? When I texture the entire template which includes everything, does UDK know I've only imported the ladder and drainage pipe thus knowing I'm only applying their corresponding textures from the template? I would think there might be a hiccup along the way since everything is tied to the one UV square. Am I just thinking too much into this? haha.
The same goes for splitting up texture sheets to save memory. If there are separate meshes that I want to import yet they all share the same texture sheet, how does UDK know I only want to utilize sections of one texture sheet for one model when there are 3 other squares full of textures?
Let's say you have a few props and a building such as this
and everything is unwrapped into one UV space like this
If I wanted to export just the ladder and drainage pipe to UDK, how does it affect any texturing I've done? When I texture the entire template which includes everything, does UDK know I've only imported the ladder and drainage pipe thus knowing I'm only applying their corresponding textures from the template? I would think there might be a hiccup along the way since everything is tied to the one UV square. Am I just thinking too much into this? haha.
The same goes for splitting up texture sheets to save memory. If there are separate meshes that I want to import yet they all share the same texture sheet, how does UDK know I only want to utilize sections of one texture sheet for one model when there are 3 other squares full of textures?
Replies
I think you should avoid bothering with this since it is straying into TD territory and it sounds like you are either doing this for fun or for your demoreel.
If you are going to anyway I recommend using a half-hour to take a look at the castle demo (epic citadel) for UDK. It is well optimised and works fine on the iphone apparently.
You will notice the textures that repeat are usually not mixed with other textures because if they are, they need to be split whenever a polygon exits the 0-1 uv space.
and here is some good reading, explains it better than I can http://unity3d.com/support/documentation/Manual/iphone-DrawCall-Batching.html
As Scruples said, however, if you want textures to tile in that situation, you'll have to add geometry at every texture break which can get expensive on the vertex side of things. It's all a balancing act...
If you're always going to be seeing all 4 textures together, then yes, you should atlas them into a single texture, to save on texture fetches. If the assets can be separated (eg. your ladder example might be used on a different building using a different set of textures), then keep that on a separate sheet. Otherwise you load the entire 2k texture just for the little portion that the ladder occupies. In which case you're wasting a lot of texture memory.
There are a lot of different considerations to keep in mind wrt to atlasing.
That makes a lot more sense. I know this is just a put into practice time of question, but thanks for the replies. I got really bogged down with the whole exporting to UDK and how the textures follow the mesh into UDK. Let me just make sure I completely understand this.....
Combining textures certainly saves texture memory, but if you need any of the textures to tile you're more or less giving yourself more geometry (more work). You just need to know if you're going to be gaining any performance increase by merging texture sheets. As far as combining multiple mesh unwraps goes, if you combine objects that you want to have reusable then don't include them in the same unwrap as everything else because you'll be importing the UV texture template that includes everything else. This wastes texture resolution for the one object you imported and wastes texture memory because you are only utilizing the one section of the entire template. Like you guys said though it's all on a per situation basis to know when to do something that positively affects the game.
As far as Light Maps go, I learned you should in fact combine multiple meshes to save render speed when baking out the Light Map. When's the best time to use Light Maps? Are they more expensive then AO maps?
just to outline:
-Only combine UVs of meshes into one texture map if they will always be near each other.
-if you plan on using one of these meshes for a different location, don't share UVs.
The reason why this is bad is because if i have 4 meshes, each 1024x1024. if i combine these into a shared 2048x2048 map and place it no where near the rest of the 3 meshes, then you have a 3 textured maps being loaded into the memory because UDK has no choice. that one little mesh's texture is shared, so udk loads that massive texture into the memory. becoming wasteful.