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In addition to baking ambient occlusion on our basic polygons, we can also model higher res objects, bake occlusion from them, and then use that as part of the texture on the lower res or low polygon pieces. This'll help add additional detail and proper shading. In this example, I've modeled these windows to fit in this opening, making sure that I've deleted the back faces. I've also mapped them straight on. If we open their UV Editor, we can see that they're basically straight on in the windows. That is I've used a planar projection.
I've made sure that these are scaled as close as possible to the original, that they are at the correct proportion. What we will do in here is add in the natural dirt we see in all the corners and crevices in the windows. Here is some reference in Photoshop as an example. In this reference of the building we modeled in previous chapters, we can see that there is lots of detail in the windows and that in the corner of the window, we tend to get, well, a lot of dirt. It also shows up as darkness underneath the top window. This is from years of sitting out here in the city and also being touched by people opening and closing it.
We want this realism in our model for a game, but we don't want to model every window. That would blow our polygon count. Back here in 3ds Max, I am set up to bake an occlusion. I will bake these high-res windows and then use that in the low res. I will press 0 for Render to Texture. For an object like this, making sure it's selected in the Name field, I'll add in an Ambient Occlusion element, clicking on Add and then choosing Ambient Occlusion. In the Ambient Occlusion, I'll make this size 1024. I would rather render bigger and then scale down.
I will put the Samples up at 128 so my gradients are nice and smooth. Finally, I'll reduce the Max distance. Remember, 0 is a special case, meaning everybody participates no matter how far apart. I'll make my Max distance 5. That way the darkness really clusters in the corners nicely and doesn't spread across the whole window. I can adjust the Spread and Dark color if needed. For this example, I will leave them alone. I will make sure that Render to Files Only is checked and I also make sure I name this file so I can find it when I go hunting in Photoshop.
I am ready to hit Render. This will take a minute, return the diffuse color and bake an occlusion. My occlusion is rendered. I don't care really about the diffuse render. What I want is the occlusion image. I'll click on the three dots for browse to file and view this. I will select the file and check View here in the Finder.
There is the occlusion for the windows. It's got good darkness around the corners and the outside and also really highlights the detail, giving depth to the window. I can do some cleanup in Photoshop and also I will make it less consistent. I'll open up that image in Photoshop and bring it onto my diffuse map. Here in Photoshop I've opened up my window ambient occlusion bake. I will Select All by pressing Ctrl+A and Ctrl+C for Copy. Then I can close this image. Here is the PSD with my color and bump ready for windows.
I'll paste it into the color group. Then I will scale it down, but first I'll change the blending mode to Multiply. That way I can see how I'm scaling. You have got some options for scaling. You can use the Scale tool or the Transform. I will press Ctrl+T for Transform. I will scale this down from the corner, holding Shift to maintain proportion. This will let me move and scale this image to fit into those windows. I will get this fitted as well as possible. Occasionally, due to the irregularities or the eyeballing of unwrapping, we need to stretch it a little bit.
I will stretch mine horizontally, just so it fits over that window polygon. That looks pretty good. I'll hit Enter to accept the transformation. I'll zoom in and check. Now I haven't added a diffuse color to the windows, but this'll really add some punch to them anyway. I can nudge this back-and-forth if needed and also I may stretch it out again. Now I have got two parts to the occlusion. I have the original dirt from the bake of the low res, plus the high res model forming an occlusion texture, giving me what looks like extra depth. When I combine this with a diffused map and a bump, these windows will really pop.
I'll save this map out and put it back on in 3ds Max to see how it looks. I'll just update the map in the diffuse channel of the material on this wall. I will press M for the Material Editor and there is my material, wall and windows. Here's a large sample. I will click on the diffuse map I have in already and just swap it for the new one. Alternately, I could've just saved over this and 3ds Max would load it up automatically. I'll pick wall section windows and hit Open.
As we can see, I have got what looks like great depth in the windows. I did make one minor goof. My polygon was upside down. This is an easy fix in Photoshop. I'll do this, fix it, and reload. We want to make sure that the darkness is in the right direction. Here in Photoshop, I can mirror this over, because it's on its own layer. Remember when you're working in textures, always use another layer. It's a better practice to do that than to have a fix that is difficult because you're trying to paint out little parts. I'll choose Edit > Transform > Flip Vertical.
Now my occlusion is laid over correctly. I can save this out again and if needed, I can erode this occlusion so it's not quite as consistent. I may also want to erode it especially along the glass so the glass doesn't read as dark. I will save this and see how it looks. Back here in 3ds Max, I've reloaded the occlusion simply by refreshing the screen once I have saved over the file. My windows look like they have a lot of extra depth. Maybe not as much as the true geometry, but definitely good for game.
After all, it's the illusion of being where we are and we need the details and the dirt in the details to make that really pop.
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