Almost all tablet cases have a rectangular opening that allows access to the screen of your tablet. The opening may have rounded corners and cut-outs for the tablet’s home button and camera, but it remains essentially rectangular.
What if you encounter a case that isn’t entirely rectangular? An example of such a case comes with the Accent 1400 communications system:
The Accent 1400 case has several aspects that don’t work well with a rectangular keyguard:
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| The left and right sides of the case bow outward. It would be helpful if the keyguard could fill this space to provide a tighter fit and to provide extra plastic for mounting the keyguard. | The camera sits well above the keyguard and part of the home button sits below the keyguard. It would be helpful to extend the keyguard into these regions to prevent access to the camera and home button, or to provide extra plastic for mounting the keyguard. |
The designer provides a way to add this additional plastic to the outside edge of your keyguard. This picture demonstrates the kind of options you have to add plastic and change the overall shape of your keyguard (it just happens to fit an Accent 1400 device):
Adding Plastic to the Edge of a Keyguard or Keyguard Frame
The following shapes can be added to the outside of your keyguard to better fit your non-rectangular case opening. Shapes are normally placed along the outside edge of your keyguard, but you can attach shapes to other shapes if necessary, as long as you end up with a single “solid” shape. You can also use the case_openings data structure to put openings in these additions.
Shapes that anchor to the edge of a keyguard or keyguard frame
Rectangles and Rounded-Rectangles
To add a rectangular shape to one or more edges of your keyguard, you will need to specify the height and width of the rectangle/square and the x and y coordinates of the center of the edge that will lie against the keyguard (the red dot). You specify a rectangle/square by using the letter “r” followed by a number from 1 to 4 based on where the rectangle/square will attach to the keyguard. To round the outer edges of the rectangle, specify the corner radius by placing a number in the “corner” column.
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Crescent Moons
There are four kinds of crescent moons that you can add to your keyguard, depending on whether you want to add one to the top, right side, bottom, or left side of your keyguard. The shape is specified with the abbreviation “cm” followed by a number that represents the side of the keyguard.
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To add a crescent moon to your keyguard, you need to specify the height and width of the shape as well as the x and y coordinates for the point (red dot) at the back center edge.
Shapes that anchor at an arbitrary location
These shapes aren’t limited to anchoring at the outer edges of the keyguard or frame. They can anchor anywhere. Most often these shapes will be anchored at the center of the keyguard to add a uniform external shape to the keyguard or frame.
Rectangles
You can specify rectangle or rounded rectangle of any size be added your keyguard. The anchor point will be in the center of the rectangle. Add a corner radius by placing a number in the “corner” column.
Circles
To add a circle shape to the keyguard, you will need to specify the height (i.e., diameter) of the circle and the x and y coordinates of its center (red dot). You specify a circle shape using the letter “c”.
Triangles
There are four kinds of triangles that you can add to your keyguard. Each of the four triangles can look like two different forms depending on whether you set the width longer than the height or vice versa. They are named beginning with a “t”, followed by a number.
The number relates to the quadrant where that the triangle would be located in an x/y plane.
To add a triangle shape to the keyguard, you will need to specify the width and height of the triangle and the x and y coordinates of its right angle. If you want to add an acute triangle shape, just put two of these triangles back-to-back.
Fillets
This swept shape can be added to the outside of a keyguard by using the “f1-4” shape name, where the number is the quadrant associated with the fillet.
Shape Reference:
Case Additions
The table below summarises every shape available in case additions.
An “x” means that column is (or can be) used by this shape; leave unused columns at 0 and the “[trim]” column can be left at [].
| Shape | height | width | corner | cut/build | [trim] |
| r | x | x | x | x | x |
| c | x | x | x | ||
| r1-4 | x | x | x | x | x |
| tab1-4 | x | x | x | x | x |
| cm1-4 | x | x | x | x | |
| t1-4 | x | x | x | x | |
| f1-4 | x | x | x | x | x |
| oa1-4 | x | ||||
| ped1-4 |
The Cut | Build Column
The “cut | build” column behaves just like its counterpart in the “openings” sections – mostly… Negative number cut away from the keyguard/frame and postive numbers add plastic. There are two significant differences.
First, all cutting and building take place relative to the underside of the keyguard – the bottom surface. You build upward from the bottom surface and you cut upward from the bottom surface. Postive numbers build and negative numbers cut.
Second, the value zero is only meaningful for building an addition and tells the designer to build that shape all the way from the bottom surface of the keyguard or frame to the top surface regardless of how far that is. Cutting all the way to the top uses a different convention. If you put a value of -9 mm or a more negative number then the designer will cut the associated shape all the way through the keyguard or frame.
Note. If your keyguard is less than 9 mm thick it’s still important for you to put a -9 value in the “cut | build” column if you’re attempting to add a concave edge to the keyguard/frame. It has to do with the way that the designer creates a consistent chamfer around the edge of the keyguard/frame.
You can use a positive cut/build number to create partial height shapes along the perimeter of the keyguard. The slide-in tab below is produced using an instruction an “r2” shape with a 2 mm cut/build value:
You can combine positive cut/build instructions with negative cut/build instructions to create a raised shelf along the edge of the keyguard. The raised shelf below is produced using an instruction with “an r2” shape and a 0 in the cut/build colum in combination with a second instruction with an “r2” shape and a -2 in the cut/build column:
Note that the keyguard chamfer extends all the way around the raised shelf. That’s because the first instruction used a 0 in the cut/build column.
You can create a concave edge to the keyguard by placing a “mirror” shape against the edge. Here, we’ve placed an “r4” shape against the same edge of the keyguard and put a -9 in the cut/build column:
Again note that the keyguard chamfer extends smoothly around the cut-out in the edge. That’s because a -9 value was placed in the cut/build column.
Using Shapes to Remove Plastic from the Edge of a Keyguard/Frame
Some cases present the opposite problem of the Accent NovaChat 5.4. Here’s a picture of the device:
There is a crescent moon shape on the left and right, but this time they extend into the case opening. To complicate matters further, the opening corner radii differ on the left and right sides. The radii on the left are larger than those on the right.
Both of these issues can be addressed by removing plastic from the edge of the case using the same shapes described above, but their polar opposites, “negative” shapes.
You specify that you want a negative shape by putting a minus sign in front of the shape name. For example “r1”, adds a with postive “corner” and a 0 cut/build value adds a rounded rectangle to the #1 edge of the keyguard. An “r2” (which would normally be placed along the #2 edge) with a postive “corner” and a -9 cut/build value, placed along the #1 edge of the keyguard, removes a rounded-rectangle shape from that edge of the keyguard:
Removing plastic can be confusing sometimes – specifically because it’s hard to see something “negative” in the display pane. Here’s an example. Let’s suppose that you want to cut out another triangle from the shape above, like this:
You insert the following instruction into the openings_and_additions.txt file (click on the image to expand it).
[ 1, "t1", 20, 30, 0, 50, coh, -9, [] ],
[Note in this example, you’ll see two “variables”. “coh” holds the “case opening height” and “cow” holds the “case opening width”. You could replace these with the actual values you specified in the customizer pane, but this approach is easier and automatically adjusts if you change the values.]
You save the openings_and_additions.txt file, but nothing changes:
You can instruct the designer to highlight the “negative” shape by replacing the value you put in the “ID” column with a pound sign, “#” (be sure to put double quotes around the pound sign):
[ "#", "t1", 20, 30, 0, 50, coh, -9, [] ],
When you save the file, you now see this:
The shape you specified is now displayed in red (you can also do this for “positive” shapes). You need to use the “flipped” version of this shape, which is denoted by a “-t2” rather than a “-t1”.
Change the shape and replace the “#” with the value you originally had there:
[ 1, "t2", 20, 30, 0, 50, coh, -9, [] ],
Save the file, and now you see what you expected and wanted:
Addressing those different corner radii
To create the various corner radii, we set the corner radius to “0” in the Customizer pane and then put four outer arc instructions into the case_openings region of the O&A file. Insert appropriate values into the “corner” column. We’ve also put a “#” in the ID column to make the cuts visible:
Replace the “#” ID value with a more appropriate one and save the file again:
Specifying the Size and Locations of Shapes
Like all case measurements, the 0,0 location for all x and y coordinates is located in the lower left corner of the case opening, and all measurements are in millimeters.
Depending on the shape of the case opening, it can be a bit difficult to visualize the lower left corner of the case opening. For example, in the example below, the green case has an opening that is wider at the bottom than at the top. So, where is the lower left corner of the case opening?
The first step is to imagine the largest rectangular keyguard that would it in this opening:
The lower left corner of this blue keyguard is the 0,0 location for all measurements.
Note: If the lower edge of the case opening is wider than the upper edge, as in the picture above, start by printing a purely rectangular keyguard that best fits the opening. You only need to print the first couple of layers of the keyguard to test the fit. This starter keyguard will help you visualize the 0,0 location that you will use to size and place all the additions you add to the outside edge of the keyguard.
Trimming a Shape
On occasion you may add a shape that extends too far beyond the edge of the keyguard. In the image below, the crescent moon shape added to the left side of the keyguard extends too far below the bottom of the keyguard because the center of the crescent moon is located below the middle of the keyguard.
You can trim the top, bottom, left and right sides of any shape. In this example, you can get rid of the spike extending from the bottom of the crescent moon by trimming all parts of the shape below the bottom of the keyguard ( trim crescent moon below zero mm).
If the crescent moon was placed higher on the keyguard and part of it happened to stick out above the keyguard (and if the keyguard is 100 mm high) you would remove that excess by trimming the crescent moon above 100 mm.
All trimming is performed relative to the lower left corner of the keyguard. That is the (0,0) coordinate of the keyguard for both case additions and case openings.
Caveats
It goes without saying that case designers aren’t limited to simple circles and rectangles. They can create cases with complex lines and cuts. By adding plastic to the outside of your keyguard, you’re just trying to get close to matching the outline of the case opening and so create as stable a keyguard as possible.
If you’re using micro-suction tape, a little extra plastic can be the difference between a loose keyguard and one that sticks well to the face of the tablet.
Straight edges and rounded corners don’t play well if placed exactly against each other:
If you experience something like this, change the x and/or y coordinate of the shape to move it closer in contact with the keyguard until the “scar” disappears.
Remember that you can include decimal numbers, such as 12.7, 18.99, and 0.005, in any of the sections to achieve the exact look you want.
Using “positive” and “negative” cut/build values in combination
The Tobii Dynavox I-16 AAC device can be purchased with a keyguard holder into which keyguards are inserted:
In order to properly fit in the holder, the top edge of the keyguard has to be cut like this:
If you ignore the circular cut, then to create this shape, you add an “r1” to the top edge of the keyguard and then cut away the bottom part of that rounded rectangle by using a shorter (negative cut/build value) “r1” shape in the same location:
After rendering the design, it’s easy to see that the “negative” shape has been removed/trimmed from the “positive” shape:
Mounting Points
Mounting methods, such as slide-in tabs and clip-on straps, place the tabs and pedestals for the clips on the edge of the basic keyguard. What can you do if you’ve added additional plastic to the outer edge of your basic keyguard?
What you should do is create new tabs and pedestals that align with the new, larger keyguard. The program allows you to manually add slide-in tabs and clip-on strap pedestals wherever you want. You create them by adding lines to the case_additions data in the O&A file.
Slide-in tabs are just half-rounded rectangles, except you’ll specify their thickness. You’ll specify the x and y coordinates, height/width, corner radius, and thickness for each tab you create. the process is described above.
There are four possible clip-on strap pedestals that you can add to your modified keyguard. Their names depend on the edge that the pedestal will appear on and, therefore, the direction of the cut:
These manually created clip-on strap pedestals are special in that you only specify the x and y coordinates for each pedestal in the case_additions section. You’ll measure for and specify the “horizontal and vertical clip width” and “case to screen depth” measurements in the Clip-on Strap Info section of the customizer as you normally would.
Keep in mind the size of the additional plastic you’ve added to the keyguard when specifying the location of these mounting points. For example, if the basic case opening is 161 mm high and you add an additional 2 mm of plastic at the top and bottom of the keyguard, like this:
The y coordinate for a tab or pedestal added to the top edge should be 161 mm + 2 mm = 163 mm. The y coordinate tab or pedestal added to the bottom edge should be 0 mm – 2 mm = -2 mm.
Finally, if you’re using clip-on straps, adding plastic to the outer edge of your keyguard and moving the mounting pedestals outward puts them closer to the edge of the case. You need to account for this when designing the clips that will go into those pedestals. You can do this by telling the program that the case is actually smaller than it really is. For example, in the example above, I’ve added 2 mm to the top edge and 2 mm to the bottom edge of the keyguard. If I want the clips to be sized correctly for this new keyguard, I just tell the program that my case is actually 2 mm + 2 mm = 4 mm smaller than it actually is before I create the vertical clips for the case. If the case is really 187 mm high, then set the “case height” in the Clip-on Straps Info section to 183 mm before generating the vertical clips.
Note: if you’re adding mounting points by hand, select “- none -” as your mounting method.
Also note: if you manually add pedestals for clip-on straps, the designer will respond to the options you select for “horizontal clip width,” “vertical clip width,” “case thickness,” and “case to screen depth” in the “Clip-on Straps Info” section of the Customizer.
Finally, note that the openings_and_additions.txt file includes variables that may be helpful to you in locating your case additions. Read more about that topic here.