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Unity3D- Is it possible to draw a circle / ellipse based on two vertices using a linerenderer?

I would like to ask if it is possible to generate and draw a circle or ellipse using a linerenderer based on two points in the scene. Specifically, these are the vertices of the mesh. For example, I would like to draw a circle / ellipse around the neck of a given humanoid.
I need something like this:
I need this circle to enlarge and shrink based on the properties of the blendshapes. If I widen the neck with blendshape, I need this circle to enlarge as well. I can draw this circle by finding the id of all the vertices around the neck and entering these vertices into the LineRenderer. But it's a very impractical way that I don't want to use. So I would like to ask if it is possible to draw such a circle that would be connected only to two points and not to all / many.
I will be very grateful for any advice.
EDIT:
I was hoping that it would be enough to connect 4 vertices in the worldspace using LineRenderer, where I would get a drawn square. And I was hoping that some rounding would be used on the edges of this square to create an ellipse or circle. For a better idea, I also added a picture to describe what I thought would be enough to use.

Mapping textures to DirectX sphere?

I am writing a virtual globe using DirectX similar to Google Earth. So far, I have completed tessellation, and have tested with a wrapped texture over the entire sphere, which was successful. I have written the texture coordinates to correspond with the latitude and longitude (90lat,-180lon = 0,0 and -90lat,180lon = 1,1).
For this project, I need to layer several image tiles over the sphere. For example, 8 images spanning 90 degrees by 90 degrees. These tiles may dynamically update (i.e. tiles may be added or removed as you pan around). I have thought about using a render target view and drawing the tiles directly to that, but I'm sure there is a better way.
How would I go about doing this? Is there a way to set the texture to only span a specific texture coordinate space? I.e. from (0, 0) to (0.25, 0.5)?

There are three straight-forward solutions (and possibly many more sopisticated ones).
You can create geometry that matches the part of the sphere covered by a tile and draw those subsequently, setting the correct texture before each draw call (if the tiles are laid out in a simple way, you can also generate this geometry using instancing and a single draw call).
You can write a pixel shader that evaluates the texture coordinates and chooses the appropriate texture using transformed texture coordinates.
Render all textures to a big texture and use that to render the sphere. Whenever a tile changes, bind the big texture as a render target and draw the new tile on top of it.

How to make 3d viewport available within a square?

How to make 3D Viewport within that 3D viewport square

You can use the Normalized Viewport Rectangles' approach, achieved by editing the Viewport Rect of the Camera.
The Documentation explains an example of split screen for a two-player game. You can adapt the explanation having the game in a particular area, and the GUI in the other screen space.
Normalized Viewport Rectangles
Normalized Viewport Rectangle is specifically for defining a certain
portion of the screen that the current camera view will be drawn upon.
You can put a map view in the lower-right hand corner of the screen,
or a missile-tip view in the upper-left corner. With a bit of design
work, you can use Viewport Rectangle to create some unique behaviors.
It’s easy to create a two-player split screen effect using Normalized
Viewport Rectangle. After you have created your two cameras, change
both camera’s H values to be 0.5 then set player one’s Y value to 0.5,
and player two’s Y value to 0. This will make player one’s camera
display from halfway up the screen to the top, and player two’s camera
start at the bottom and stop halfway up the screen.

Filling a pie slice of a rectangle

I want to fill a slice of a rectangle based upon a value which doesn't correlate to the degree of the rectangle that needs to be filled.
Say this square below, I would want the area that is light gray to get bigger and bigger (Like a slice of a pie getting bigger) until the entire square is light gray.
How would I go about doing this using System.Drawing? I tried using FillPie but it doesn't fill the square corners

Set the Graphics.Clip property to a region that represents the rectangle, then FillPie with an oversized radius such that the "pie" completely covers the rectangle.

Cut holes in a Texture2D

I want to know how to remove part of a Texture from a Texture2D.
I have a simple game in which I want to blow up a planet piece by piece, when a bullet hits it "digs" into the planet.
The physics are already working but I am stuck on how to cut the texture properly.
I need to create a function that takes a Texture2D a position and a radius as input and returns the new Texture2D.
Here is an example of the Texture2D before and after what I want to accomplish.
http://img513.imageshack.us/img513/6749/redplanet512examplesmal.png
Also note that i drew a thin brown border around the crater hole. If this is possible it would be a great bonus.

After doing alot of googling on the subject it seems the best and fastest way to achieve the effect i want is to use pixel shaders.
More specifically a shader method called 'Alpha mapping'. Alpha mapping is done by using the original texture and another greyscale texture that defines what parts are visible or not.
The idea of the shader is to go through each pixel in the original texture and check how black each pixel in the greyscale image is at the same coordinate. The blacker the pixel in the greyscale picture is the higher the alpha value (more visible) the pixel in the original texture becomes. Since all this is done on the GPU it is lightning fast and leaves the CPU ready to do the actual logic for the game.
For my example I will create a black image to use as my greyscale image and then draw white circles on this corresponding to the parts i want to remove.
I've found a MSDN examples with working source code for XNA 4 that does this (the cat example):
http://create.msdn.com/en-US/education/catalog/sample/sprite_effects
EDIT:
I got this to work quite nicely. Created a small tutorial with source code here: http://syntaxwarriors.com/2012/xna-alpha-mapping-with-pixel-shaders/

A good way of doing this is to render a "hole texture" using alphablend on top of your planet texture. Think of it like drawing an invisibility circle over your original texture.
Take a look at this thread for a few nice links worms-style-destructible-terrain.
To achieve your brown edges I'd guess you'd need to take a similar approach. First render the hole to your terrain with say radius 10px. Then you render another circle from the same origin point but with a slightly larger radius, say 12px. You'd then need to set this circle to a blendmode that results in a brown color.

look at my class here:
http://www.codeproject.com/Articles/328894/XNA-Sprite-Class-with-useful-methods
1.Simply create an object of Sprite class for your planet
Sprite PlanetSprite = new Sprite(PlanetTexture2D , new Vector2(//yourPlanet.X, //yourPlanet.Y));
2.when the bullet hits the planet, make a circle texure2d by the center of collision point using "GetCollisionPoint(Sprite b)" method
-you can have a Circle.png with transparent corners
-or you can create a Circle using math(which is better if you want to have bullet power)
3.then create an Sprite object of your circle
4.now use the "GetCollisionArea(Sprite b)" to get the overlapped area
5.now use the "ChangeBatchPixelColor(List pixels, Color color)" where pixels is the overlapped area and color is Color.FromNonPremultiplied(0, 0, 0, 0)
-note you don't need to draw your circle at all, after using it you can destroy it, or leave it for further use