Object Fundamentals - Part 4
"Look! Christ of the Andes!" says Caddy.
"Oops! Sorry! I was playing with my shadow.
"Let's get a little technical. This is stuff you want to know if you're going to make your own artwork for objects.
"The basic grid pattern is a bunch of squares, 128 pixels on a side. Take a square, rotate it 45 degrees to get a diamond, and squish it to half its original height. A wall section fits along one edge of the square. A floor covers one square. And a one-square object fits exactly inside the square.
"This is not a perspective view; the lines don't converge at a vanishing point. Instead, it's an isometric view with the lines sloped 26.565° from horizontal. That odd angle is what comes out from squishing the grid with a 2:1 ratio.
"This same grid pattern shows up in all the games that use a constant look-down angle. It's the same for all the Maxis simulation games, and for the more cerebral simulations like Civilization. The 2:1 ratio is popular because it makes it easy to address a given spot on the base map without doing a lot of trigonometry. You can establish a basic grid, say 32 x 32 pixels, and then just snap image tiles to the grid where they belong and it all tiles perfectly! No extra CPU time, and no numerical instabilities.
"So if you're creating your artwork in 2D, just lay out a grid pattern like this and you'll do fine. Here's a simple reference grid image that you can download if you like; it's a 16K GIF file. Or if you have a straight-on view that you want to fit onto the end of an object, all you have to do is squish it 50% in width and skew it 26.565°.
"If you're working with a 3D modeling program, you'll want to know the exact viewpoint. Working through the trigonometry, it turns out to be fairly simple. You want to render your object -- isometrically if you can -- by first rotating it 45° about the vertical axis and then setting your viewpoint exactly 30° above the horizontal plane.
"You can work it out for yourself. The 45° rotation is pretty obvious; the guidelines are symmetrical left to right, so it has to be 45°. For the viewing angle, you want the angle whose sine is 0.5, and that turns out to be 30°.
"Didn't realize you were up so high, did you? I think the most common mistake people make in objects for The Sims is using a picture shot with the viewing angle too low. That's why table tops often look slanted, and other objects look like they're about to fall over.
"If you can't get your 3D modeler to do an isometric view, then back wa-a-a-a-ay far away and use a telelphoto zoom to view the object. That will minimize the perspective, and you'll still be able to create a picture that will look good in the game.
"And that's all there is to it! Well, not quite all; there are still lots of techniques to learn for creating the images of the objects, making the z-buffer work, and what utilities are available to help you do all this.
"Before I send you off to those tutorials, let's review the main points I wanted to cover here:
"Got all that? OK, now you're ready to understand what folks are talking about in the tutorials about how to make objects for The Sims. Here are some of my favorites.
"And with that, we're all done with this essay! Thanks for listening! Now it's time for me to have some lunch."
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"Pasiphae, did he really say he likes it?"
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