Jennifer's Classroom

[Junee]

So another soldi... uhm I mean another hedgehog joins the group!

igelkott.png (42.08 KiB) Viewed 5061 times

I'm off to make a hedgehog-free landscape. kthxbye!

[Jojon]

...hedgehog-free...

Aawwww.

[Jennifer_P]

That is so cuuuute! And huggly!

[Sophia]

It's adorable! Want want want for my Relto, together with a squee and quab!

[Jennifer_P]

Lesson 10
First, please note that this tutorial is intended for Blender 2.45 and will require updating for version 2.46 of Blender.
Today we will be learning about the why and what of UV mapping. This is a really important subject because nothing makes an Age look realistic faster than really great texturing/UV mapping, and nothing makes it look icky faster than poor texturing/UV mapping. Which is why we'll be spending a couple of lessons working on the topic.
So what is UV mapping? Well, it's the process of getting a two dimensional square image to wrap around three dimensional objects. Since most 3D objects aren't flat, this creates some problems. Imagine taking a sheet of paper and trying to wrap it around some of the objects lying around you...could you get the paper to lie perfectly flat over the objects' entire surfaces, or would you instead get wrinkles, folds, and perhaps even tears if you tried? Perhaps you would even need to cut the paper with a scissors to get it to lie flat. Probably you would get a lot of crinkles and messiness, especially if the object had a very complex surface. And just as in the physical world you would get wrinkles and tears if you were to wrap a paper around a complex 3D object, so in the virtual world you get squeezing and stretching on the image if you try to wrap a texture around a complex 3D object.

Now, one of the main purposes of UV mapping is to reduce this squeezing and stretching. But before we work on the solution to these distortions, let's think about them a little more closely. To whit, squeezing/contraction is simply when the texture is all pinched together and shortened and squished, whereas stretching/extension is the opposite of that; it occurs when the texture is pulled apart, over-extended, or smeared-looking. This is a worse type of distortion than squeezing/contraction because while squeezing/contraction at least adds more detail (too much detail being the problem) to an area, stretching/extension leaves less detail in an area with the possible consequences being visible pixels showing (pixelation), a really up-close and personal view of the texture image revealing the faults in the texture you used, smearing of the texture that makes your model look like it was textured with a barcode, and a blurry and undetailed look to the affected area, all of which adds up to unrealism--blech! And this is not all that you have to worry about when you're texturing!

There is one final danger as well--seams. Sometimes in order to cover an object with a texture (which is to say, to UV map it) you (or Blender) need to make a "cut" in the texture. This cut results in the creation of a discontinuity on the textured model between the texture on one side of the cut and the texture on the other side of the cut (called a seam). This is the same effect you would get if you snipped up a piece of flowery fabric into squares and then randomly placed two squares next to each other: the flower patterns on either side of the cut would no longer match across the cut. And for the same reason a texture pattern won't match across a seam.

So now you're probably wondering, "Okay, then how do I avoid seams and extension and contraction?" Well, it's kind of a Scylla and Charybdis situation, actually...See, one of the ways to get rid of extension and contraction is to create seams. Then the trick is just to hide the seams the best you can, and there are a couple of sneaky ways to do that. But for now, let's learn how to detect distortion and seams.

Using a grid to detect distortion
Well, open up Blender with a fresh cube and let's get ready to texture: Split the screen into two halves, and set the right half to be the UV/Image Editor. Change the View Mode of the left hand window to UV Face Select (if you don't see this option, you probably have Blender 2.46--this tutorial uses 2.45). Now, over in the right hand UV/Image Editor window, click on the menu option "Image" and in the menu that pops up click "New". A little window will pop up, and at the bottom of this window click the button that reads "UV Test Grid". Surprise! A pretty little black and white squared grid with pretty little rainbow crosses in the centers of the squares should now be covering your cube. What might this strange pattern be for? Well, sometimes it can be hard to see where seams or distortion are occurring on an object, whether due to a dark or fairly uniform texture or other reason. But one thing's for certain--when they're in the game and large as life, EVERYONE will notice the faults. Fortunately, with the help of a grid of squares distortion and seams are easy to detect, because if a texture is squeezed or stretched the squares will turn into rectangles or diamonds or parallelograms. So our grid is a simple distortion-detector.

Distorting the grid...Rendering the grid
To convince yourself that the grid is useful for detecting distortion, go back to Object Mode and make sure that you're viewing your model with "Textured" turned on instead of "Solid", which is the default. Now, head into Edit mode and pull a single corner of the cube out and away from the rest of the cube. Jump back into Object Mode and take a look--see the extension in the texture now? Now try creating some contraction. It's a lot easier to make than it is to fix, huh?
Well, let's try to do a quick render of the cube. So in the menu bar up top with "File", "Add", etc, choose the menu option "Render" and click "Render Current Frame". Let it render just enough to see that there is no texture showing on your cube (doesn't that just make your blood run cold?) and then press ESC to cancel the render and close the window. So how do we get it to work? Well, to make this particular texture show up in a render you have to have the "TexFace" button selected. This button happens to be in the Material section of the Shading section of the Buttons window (which you access by clicking the grey sphere and then the red sphere--hover your mouse over the buttons to see the names I'm referring to). Anyway, in the Material subwindow (where you would normally go to change the color of an object) of the Material section, there are seven little buttons in two rows, and on the first row you will find "TexFace". Select it and render again, and you will see your texture.
Well, that's it for today. Tune in next week for the exciting conclusion of "UV Mapping Madness!"

[Jojon]

I'm not so much worried about the tears in the paper as the tears in my eyes. :)

[Jennifer_P]

Tears of amazement that I actually updated this, I trust?

[Jojon]

Just plain old tears of UV frustration, I'm afraid -- I have complete confidence in your 1337 JIT tutoring skillz. :)

[Junee]

B2-B4

...what? The pieces are all that's missing. It's almost scary how quick those little squares loose their squareness. *passes out napkins*

[ametist]

Jennifer, it's a pure joy to read your lessons!! One gets filled with energy and suddenly Blender don't act as evil as it like to do I much enjoy to play with those little squares, going from square to rectangle to polygon to rectangle and then .... where did the squares go? /scratchhead