This is a very important part of the room, as it is visible most of the time in open areas. It's interesting to make it low poly, but not so much that it looks blocky. To save performance, the part that is not visible can be deleted, this optimization reduces the load on the CPU (especially in dx9).
To create moving clouds we can clone the main skybox to be a little smaller in size, and use it as the new clouds. New textures should be assigned and then a mask using map_d in the .mtl file (SMD). Multiple cloud layers can be created to build complex skyboxes, but this can add some issues if SMX hierarchy is not tweaked properly.
After that start working on sun lens flare, bloom, and other effects which can be placed in front of the sky models to be always visible, or behind cloud layers to make it appear and disappear based on the clouds position.
For me exporting as tga 24bit with compress rle checked shown the best result/size ratio, while dxt1 is smaller it can produce artifacts when we look closer. For a big model, that most of the time will be visible I tend to choose the best quality from tga as the difference to dxt5 is not a big deal.
The dxt5 and tga 32 are only useful for models that will use alpha. Using tga 24 with compress rle checked really helps to drop the size compared to 32, without loss in quality (apparently).
Fog (LIT)
It's important to know that LIT can direct affect how the skybox will look. Depending of the fog setting, we can have color interaction in the horizon. The bigger the skybox, the most impact the fog will have in the distance. There are a few fog settings, but I'm only used to two of them:
Fog type 2
It's useful for scenarios where the light is more consistent, like interiors and closed areas. The type 2 is also good for raining areas as it doesn't hide the skybox, and fills the area next to Leon, looking like water particles suspended in the air. When using Type 5 in raining areas it can look to dry next to leon, or the fog can prevent the skybox to appear in the distance.
Advantages
• Works well for interiors.
• Skybox color is less affected than exponential fog types.
Disadvantages
• Not good to fix pop-in in the distance for open areas.
Fog type 5
It can be useful to achieve more contrast. I've used it in r10b, my intention was to keep the lake dark, and the type 2 was not working well. The lake was too bright when the skybox was ok, and the skybox was too dark when the lake was ok. With type 5, the skybox received the right amount of fog while the lake kept dark.
When the fog is disabled the whole map looks fake and small, the fog mislead our brain in a good way to add depth and the sense of distance, so the right balance is important. Remember Grand Theft Auto trilogy? That's why fog is needed!
Using Type 5 the objects next to Leon are less affected by the fog, while the skybox will be more affected. It works by increasing the amount of fog in a exponential way, so that's why it create issues. If the color of the fog is dissonant from the artistic look we are aiming for, it can end up ruining a good skybox.
Generally I tend to use blue or a neutral fog. There aren't that many uses for a redish fog other than in a Stage with lava like the dragon room. And even there the blue fog can make it's job if we'll implemented. I think the blue tends to blend better with the models, rather than red or other warm colors. However blue and red can work togheter to create contrast, a good combination is making the light sources warm like orange and then apply a blue fog over it.
Advantages
Disadvantages
• Can affect how the Skybox looks (opacity and color wise, more than type 2).
• Not that good for interiors in my opinion, but may have some application depending on the situation.
SMX
Although it's not recommended, the SMX is one way of tweaking the appearance Skybox. It can be used to match color of the fog, making everything cohesive. Just keep in mind that if the Skybox is not interacting with any lights this SMX tweak will be useless, should use vertex color instead.
ARGB (SMD) Vertex Color
This complementary file can be used to increase the brightness of the sky, and to change its colors if needed. Similarly to SMX, it affects the colors of the model, but when it is not being hit by any light, while SMX controls the color that the model will present when there are light interaction.
Let's say if there's no skylight in our room, or if it was set off for the skybox, it's possible to use ARGB to add brightness without the need of any lights. For example, an interior area with outside view can have ARGB added to the skybox to look much brighter, without the need of a big radius light, which would force us to deal with light switches, or flags to ignore lights for the interior models using SMX.
Draw distance (LIT)
Originally the game only loads objects only to a certain point, but thanks to a HEX code by Futon, we can now increase this limit. Before, when disabling fog it was possible to see black artifacts in the horizon, and corners of screen as the camera was rotated.
These are the boundaries before the game simply starts to ignore anything further, thus creating a strange artifact in the horizon when dealing with huge skyboxes like in r605 and r606.
With that out of the way, is now possible to have massive skyboxes without side effects. This allowed me to add to such rooms the level of detail in the distance they have. Before that, the effect of the castle lights was disabled to a certain point even with max draw distance set in the LIT file. But now we can simple place the fog far away without issues.