....but if you know of a way to properly map a rectangular texture area (four sides) onto a parallel trapeze (also four sides - great!...or so you'd think.), without a triangle splitting them and spoiling the broth by adding a fixed diagonal edge, I'd love to hear it.
Heh, well if you can't figure it out I doubt if I could, but if you send me the packed .blend file I'll give it a shot at least.
(When editing UV-maps in the UV/image editor, make sure to tick the "View->Update Automatically" menu entry in the UV/image editor pane -- this will make your edits show up in real time, in any view windows [i.e. while you're dragging stuff around, as opposed to not until after releasing the button].)
Wow, I wish I'd known this earlier. Great tip!
:lol: That's how you write chessmoves (for pawns).
Oops! Well maybe that's a good puzzle idea.
Your table looks nice, Junee; you've chosen a good texture. Have you tried the "Cylinder from View" unwrapping option for those table legs?
Lesson 11Note: this tutorial works for Blender 2.45; it will need to be updated to work for version 2.46.
Okay, pay sharp attention today because this lesson discusses the very foundations of UV mapping!
Basically, we'll be looking at one of the main causes of texture distortion and stretching/extension.
So let's open up Blender and get started with a fresh cube and a quick review. We're going to be texturing, so set the screen up for that task. (Split the 3D View window up into two windows, change the right window to be the UV/Image Editor window, and change the 3D View window from being in Object Mode to being in UV Face Select Mode. Tada!) We'll also be using the same Blender grid texture today that we used in the last lesson. Remember how to access that? Well, in the UV/Image Editor Window, go to "Image", choose "New", and hit the "UV Test Grid" button. Your cube should now be coated with that checker pattern. Incidentally, did you notice that we never changed the Draw Type from "Solid" to "Textured"? Check out how the cube looks in Object Mode: no texture showing! You'll have to set the Draw Type to "Textured" to get it to show up in Object Mode. And while you're at it, try rendering (the Render menu option is up by the File menu option; just click "Render", and then choose "Render Current Frame"). Yikes, no texture in the render either! Well, just remember the last lesson--you have to hit the "Texface" button for this texture to show up in a render. The "Texface" button is located in the Material subwindow, which is one of the five subwindows that pop up when you click the red sphere button (technically known as the "Material buttons" button).
Okay, enough review, let's start some UV mapping!
To unwrap an object, you need to be in UV Face Select Mode (at least, for Blender 2.45 you do), so switch back to that from Object Mode. Ready? Now choose the menu option "Face" (located in the 3D view window's header bar) and in that menu choose "Unwrap UVs". Immediately a window will pop up asking you how you would like your UVs unwrapped, and you would like fries with that? Tell it no; Blender's fries are awful.
...Anyway. The unwrapping option that we'll be working with today (we'll look at more options later) will be "Project from View", which is a planar form of projection.
But just what is a planar projection? And what has projection got to do with anything in the first place??? Well, let's try a little thought experiment to help clear this up. First, imagine that you have a slide projector showing a colorful picture of a still life fruit bowl scene. Now let's imagine that you are holding a large white cube. You walk in front of the projector screen holding the cube. Now what happens to the cube? Light is projected onto it from the slide projector, reproducing a part of the still life scene on the faces of the cube which are pointed towards the light. If you hold the cube straight and level so that one face is pointed directly head on towards the projector, the still life picture looks nice and proportional. But now suppose that you tip the cube so that the projector's light strikes the face of the cube at an angle. Is the still life picture still nice and proportional? No, it is elongated and stretched out. Like this:
http://www.pbase.com/shootin/image/56881709 Or this flashlight circle, which should be circular but is instead an oval:
http://www.outdoors-magazine.com/local/cache-vignettes/L328xH246/aurora_beam-6b022.jpgSo what happens if you tip the cube even more? The picture on the face becomes even more stretched and elongated. And eventually, if you tip the cube far enough so that the cube's face is almost pointing away from the projector, there is nothing more to be seen of the still life except some colorful streaks of light smeared across the face of the cube. But what does it all mean?
Well, in this scenario, the still life picture would be like our texture: and we are "projecting" the texture onto the faces of our cube. And just as smears are produced when the light from the slide projector strikes the face of a physical cube from a wide angle, so also do texture smears result when a texture is projected onto a virtual surface at a wide angle.
http://www.pbase.com/shootin/image/56881709So to sum it up: when there is a wide angle between the projection direction (the direction the beam of light is pointing in) and the surface on which the light is projected, the texture is elongated as a result. Actually, if you want to try an experiment to see how this works, take a flashlight and draw a smiley face on the lense with a marker (washable). Then shine the beam on a flat surface and change the angle at which you shine it at. When the projection direction of the flashlight beam is almost parallel to the target surface, the smiley face will be really smeared out and the circle stretches out into an oval! But if the projection direction of the flashlight beam is almost perpendicular to the surface, then the circle is nice and unstretched and the smiley face is happily proportional.
Now, about why the "Project from View" UV mapping option is called planar. Basically, if the texture is projected from only one direction, it is called "planar" because the texture is projected onto an object from a simple flat "plane" view. There are other types of projection methods in which you basically take the texture and roll it into a cylinder or sphere around the object to be textured and then project the texture inward--but we'll get to these later.
UV Mapping in BlenderSo let's try some planar mapping out in Blender, shall we?
First, make sure all the faces of your cube are selected (they will be a light purple color when selected; hit the "a" button a couple of times with your mouse in the 3D view window in order to deselect and reselect the cube a few times and you'll see what I'm talking about). Got the faces all selected? Now turn the cube so that one face is directly facing you head on in a perfect view (Top, Side, or Front, it doesn't matter--and remember you can find these viewing options in the View menu option of the 3D View window). So go ahead and hit "Face", "Unwrap UVs", and observe the option "Project from view"...And what "Project from view" means is "Project the texture from my point of view, as if I'm a human flashlight shining onto the cube." Well, click "Project from view". As Anna would say, "What do you see?" Do you see a perfect grid covering the face of the cube which is directly facing (perpendicular) to you? So far so good, right? Okay, so let's rotate the cube and--Aiiiieeeee!!! Horrors, we've got streaks on four faces of it! What happened??
What happened was that those four faces were at a large angle to the projection direction--in fact, they were parallel to it. And when projected, faces that are parallel to your projection direction will get long streaks on them; faces that are perpendicular to your projection direction will get perfect textures on them. Faces that are somewhere in between being parallel and being perpendicular end up looking better than streaks but worse than perfect texturing--usually they just end up being elongated and stretched out, with the distortion worsening or being mitigated as the angle between the projection direction and the textured face grows or shrinks.
Here is a bit of Blender mapping practice plus a problem to try out:
1. Using the default Blender grid, texture a cylinder from the side. Where and why do you see smears on the cylinder?
2. Now texture a sphere. Where and why do you see smears on the sphere? Where is the distortion the worst? Where is the texture the least distorted?
3. Finally, without actually doing this in Blender...How would you texture Suzanne the monkey head so that there is as little distortion as possible on the top of her head? On the side of her head? On the front of her head?
Now try this out in Blender and see if you are correct.
That's how you write chessmoves (for pawns). 
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