Brush Clipping in SinEd - Part III by Eutectic
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1. The concept of 3-point clipping
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Back to the basics
Ok, my goal here is to make you understand how 3-point clipping works. But for this, you absolutely have to be able to visualize it in 3D to understand what's going on when you use it. So we have to go back to the basics of a clipping plane from the introduction in Part I and work our way from there.
Here's our basic clipping plane. It's only defined by 2 points at this stage:
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Figure 1c: Graphical representation of a 2-point clipping plane.
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Now just imagine that the orange line traced between the 2 points is a pivot around which the plane can revolve just like a door on a hinge. So that plane is basically able to rotate by 360 degrees around its "hinge" right?
But what if we want to set this plane in 3D space so that it can't rotate and that its orientation is completely fixed? What's missing in this picture?... Another point of course! But that point can be anywhere in space except on the orange line. So let's place one at random, say here:
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Figure 2c: Placing a 3rd point in space.
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Now let's rotate the plane around its "hinge" until it intersects with this 3rd point in space:
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Figure 3c: The plane is rotated to intersect with the 3rd point in space.
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And that's all there is to it. If you can visualize this well, you can use 3-point clipping to cut any brush at any combination of angles you want.
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2. Using 3-point brush clipping in SinEd
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Let's finish that tapered brush already!
At this point, the best way to demonstrate the use of 3-point clipping is to complete the tapered end on our brush by making those "impossible angle" cuts of course.
So let's pick up where we left off. We know that we need a clipping plane that is angled 45 degrees vertically and 45 degrees horizontally to do the cuts. You could do this in any order in fact but let's start with the vertical angle component since it's the easiest.
Switch to the XY 2D top view, select the brush and place the first 2 points to form a 45 degree angle:
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Figure 4c: Drawing the first 2 clip points - 2D XY (top) view.
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Let's take a look at the 3D view enhanced with my graphical representation of the clipping plane in its present location and orientation:
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Figure 5c: The present position and orientation of the clipping plane - 3D view.
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So what we just did was to create a vertical clipping plane oriented at 45 degrees. The location of the points is important here and even though it looks like we're about to clip a big chunk of the brush away, remember that the actual clip isn't done yet. So make sure that your points are in the exact same locations as the example above. Remember: if they're not, you can move them around as much as you want by using Shift-Rightclick-Drag.
The idea now is to add an additional 45 degree component to the angle of our clipping plane, this time horizontal. We want to rotate that plane around its "hinge" until it reaches the proper angle by adding a 3rd point on which it can lock on to. In order to obtain the desired angle, the point will be moved to a known reference.
Generally, the best way to go about this is to insert the 3rd point in the same view as the first 2 points (the top view in this case). This will automatically place it at the same height as the other points.
Please note that the 2D view doesn't automatically hide you the part of the brush that will be clipped when using 3-point clipping. Keep this in mind and we'll come back to it in a short while. Draw your 3rd clip point in the location shown below:
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Figure 6c: Drawing the 3rd clip point - 2D XY (top) view.
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Switch to the XZ side view. Note that the 3rd point is at the same height than the first 2 because it was inserted in the same view. What we need to do now is move the point to a known reference. Since you want your new face's lower edge to match up with the lower edge of the already existing tapered faces, you can use one of the corners created by the previous cuts as your reference.
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Figure 7c: The 3rd clip point waiting to be moved - 2D XZ (side) view.
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Now move the point to your known reference as shown below:
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Figure 8c: Moving the 3rd clip point in position - 2D XZ (side) view.
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Here's the 3D view enhanced with my graphical representation of the clipping plane once rotated to its desired orientation by the 3rd clip point. Don't do the clip yet though.
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Figure 9c: The clipping plane is now oriented properly but the clip is reversed - 3D view.
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Ok, what's wrong in the picture above? Simple, the part of the brush you want to keep has disappeared, only its outline can be seen. So if you clip now, you will lose the part of the brush you want to keep and be left with only the part you want to remove.
This is how you will be able to tell which side will be clipped before you do the operation: always check your 3D view! You can't rely on your 2D views for this. It's very important to remember this otherwise you could lose your whole brush and have to start over.
Now do a clip flip (keypad slash) to invert the clip operation and observe the result:
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Figure 10c: The clipping plane is now oriented properly and ready to rock - 3D view.
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Another thing worth mentioning here: by comparing the picture above with Figure 5c for example, you can see right away that the part of the brush that will be clipped is not automatically hidden as when using 2-point clipping. Therefore, the actual outcome of the operation is not as readily obvious. So it's a wise move when using 3-point clipping to casually do a couple of clip flips while looking at your 3D view to determine which option makes the most sense. The main guideline is: whenever you see an outline-only brush portion (as in Figure 9c), you can be sure that part will be removed. So if that part happens to be the one you want to keep (as above), then it's necessarily the alternate option.
Now hit ENTER to perform the clipping:
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Figure 11c: The clip is preformed - 3D view.
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And admire your work:
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Figure 12c: The first face is done - 3D view.
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So all that's left to do now is to repeat the operation 3 more times for each of the remaining sides working your way around the cylinder in a clockwise fashion. Each time, take care to place your 3rd clipping point in the right spot using either one of the side views. And don't forget to check your 3D view and clip flip also. When you're done, you should have a brush that looks like this:
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Figure 13c: The final product - 3D view.
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6. Afterword
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3-point clipping in SinEd is a truly powerful feature not found in every editor. It enables the map designer to create almost any shape imaginable when used to its full potential. However, it must also be used with caution because it also makes it easy to create solids with an overly large number of odd angled faces or solids with an excessive amount of faces. And typically, the Qbsp and Qvis compilers often have a problem with those. So the bottom line here is: use 3-point clipping wisely, enjoy it but don't go crazy with excessively complex brushes.
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Part II
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