This is a tutorial by Steven Worley on using the Forms Editor in Imagine. Its original distribution was on the Imagine Mailing List, and may be freely redistributed subject to the restrictions found at the end of this text. --------- The creation of objects in Imagine is certainly not as intuitive as the process you used in kindergarten to squeeze clay into vague animal shapes. Instead of a real life view of the object, you get a complex quad-view display. Instead of using your grubby fingers, you have a very 2-D mouse. Most importantly, if you wanted to change the shape of a clay model, you just pushed and pulled on it. In Imagine (and any other computer modeler) you have to use a very specific set of tools to manipulate your objects. No matter how powerful these tools are, they are still going to limit the ways you can manipulate your creation. This tutorial is a taste of the Forms editor. The editor is VERY powerful, but not necessary easy to describe. It allows you to create certain types of detailed object shapes quickly and easily, and is certainly not limited to the asteroid-like example in the Imagine manual. --------------------------------- Part I- What IS the Forms Editor? --------------------------------- You might have noticed that Forms has in essence NO description in the Imagine manual. The manual's tutorials do not describe how the Form Editor works or why you should use it other than "It is very powerful" and "It can make organic forms easily." I don't blame Rick Rodriguez- the Forms Editor is difficult to understand and hell to explain even in person. It is very hard to describe how the Forms Editor works. It uses a very strange method of defining it's objects that is difficult to put into words. You might want to re-read this explanation a few times, since the Form Editor is much easier to control when you know what it is doing and how it determines your object's shape. The Forms Editor defines it's objects as a set of varying radii cross-sections. You have a great amount of control over both the shape and size of these cross-sections. Think of an orange, and the wedge-shape segments that make up the orange's cross section. If the orange wedge were in the shape of a square instead of a half-circle, the orange would become a cylinder instead of a sphere. If you make the square wedges in one direction a different size than the wedges at 90 degrees to them, the orange distorts into a squashed cylinder which looks like an oval from the top. If you define the wedges to be square in one direction and crescent shaped the other (90 degree) direction, you will get an orange shaped like a cross between a cylinder and a sphere- the resulting object is something like a sphere with two ends sanded to a smoothly beveled edge. Another way we might mutate the orange is instead of changing the shape of the wedges, we can change the radius of each wedge as we look at them from the top of the orange. If the wedges on the front side of the orange have a larger radius than the rest of the wedges (but the same shape), the orange is going to look like it is ballooning with air pressure with one swollen side. If the radius of each wedge changes as you go around the orange (perhaps an alternating big-small-big-small), the orange will take on a fluted, star-like horizontal cross-section. Any vertical cross-section will still be circular. Got that so far? Well, this is exactly what the Form Editor allows you to do. You can define a the shape of these wedges in both the front-to-back and left-to-right directions, as well as having completely independent control over the radial size of these cross sections. When you mix these abilities, you can produce an AMAZING number of complex shapes, especially since each wedge can loop up and down and form holes and cross over itself. No tree ever made an orange with the peel intersecting itself, but the Forms editor will gladly create a shape like this for you. The Forms editor handles all of the details and bookkeeping, and lets you worry about your form. The actual mechanics of producing the object are a bit complex, though straightforward. There are four user-defined cross sections (at 0, 90, 180, and 270 degrees, looking from the top) each with the same number of points defining it. Every section around the orange comes out at a certain angle (like 45 degrees) and its cross section is interpolated from the four pre-defined cross sections (probably linearly, it's hard to tell). For the 45 degree example, the cross section would be formed by taking the 0 degree and 90 degree user defined cross sections and assigning each 45 degree cross section point a position mid-way between its corresponding location at the 0 degree cross section and its location at the 90 degree cross section. Thus, the cross section will smoothly change from one shape to another as you move around the form. Once the vertical cross section is determined, they are scaled radially by an amount given by the radius of the user defined HORIZONTAL cross section (the top view). An area where the horizontal cross section has a radial bulge will cause the wedge at that point to stick out a bit more. These bulges can be as severe as you like. Instead of a bulge, it is easy to make a sharp knife point. This method of defining objects gives you an amazing amount of control. The radial control alone is completely flexible, allowing you to use negative radii, or move the points so that the outside surface actually reverses itself and backtracks. The vertical cross section is equally malleable, allowing you to make self-intersecting walls that are either closed or tube-like. [Or both!] That's it! The user defined vertical and horizontal cross sections completely determine the shape of the object. It is very useful to know how the form is actually constructed- it is not easy to figure out, and the documentation does not describe the method at all. Once you understand how Imagine makes the object, you can actually plan how to build a specific shape. One great advantage to the Forms Editor is the fact that the form is continuous- it is made one piece. This means that making smoothly rounded corners is easy. Organic forms in particular do NOT have sharp right angles and flat planes in them, and are particularly well suited to creation in the Forms Editor. Any object created in the Detail Editor tends to be made of extruded or primitive objects joined together- there is rarely any smooth transition between the joined segments. -------------------------------- Part II- Use of the Forms Editor -------------------------------- The actual creation of these cross-section forms is pretty easy. The Form editor is particularly fast in it's response, since the tri-view does not have as many points to update as the view in the Detail Editor. When you start up the Forms Editor, you have the option of loading in an old form or starting a new one (By choosing "load" or "new" from the Object menu). You have a decision when you make a new object on whether you want an X-Y cross-section or an X-Z cross section. The X-Y option makes your object like the orange- the segments are all arranged around the vertical axis. X-Z orients the object on its side, like a piece of wood on a lathe. (The Form editor can emulate a lathe very easily, but is much, much more versatile.) Most of the time you'll want an X-Y cross-section, but everything works similarly for an X-Z. You also have a choice on how many points and cross sections to add. The "# of slices" is NOT the number of orange segments, but the number of points that defines each orange segment. The "# of points" is the number of orange slices you have. These labels are defined sort of backwards, but if you confuse them it is easy to fix. I feel the default numbers are very large- its easier to start with a simple version of your form and add points later for detail. It is EXTREMELY easy to increase (or decrease) the number of points and segments later, so I usually start with something like 12 points, 8 sections. Again, this is easy to change later. If you start with many points, it takes a considerable amount of time just to move each of the points into your coarse shape before you refine details. The default start up form is that of a sphere with two small holes in it at the top and bottom. The Form Editor does NOT display objects in it's triview like the stage and detail editors do. It shows the vertical cross sections (the orange wedge shapes) in the front and right views, the horizontal cross section (wedge radius as you go around) in the top view. The perspective view is accurate, and you can select wireframe, solid, or shaded mode by using the View menu just like you would in the other Editors. I prefer solid because many forms get very complex very fast, and it is difficult to see the basic structure in the wireframe mode. To manipulate a cross section, you just grab a point and move it to where you want. You can change all FOUR of the vertical cross sections- if you look in the bottom views, each cross section is a separate string of points. If you select a point, it's corresponding points on each of the other cross sections will highlight for comparison. You can define each cross section completely independently- the front view will let you manipulate the cross sections of the orange at 0 degrees and 180 degrees, and the right view will let you set the 90 and 270 degree cross sections. Note that the 4 cross sections are not connected at the top and bottoms. You are free to move the top and bottom away from the center axis. Moving the points so they lie on top of each other on the Z axis will cause the object to close at that point. Moving one or more points away from the axis will cause a hole or entrance to the center of your object to appear. This allows your object to be open at the top and/or bottom, so you could have a tube or bowl instead of a sphere. If two opposing cross sections (like 0 and 180 degrees) touch and the other two do not, you will end up with an object with an intersection in the shape of a bow tie. If you do connect any of the points (you can connect in the middle, too!) you might want to make sure they are EXACTLY on top of each other and then use the Detail Editor MERGE command when you're finally done with design. This will decrease the file size of your form, increase rendering speed, and increase the ability of the Phong shading. Most of the time you don't need to control each individual point, and if you were making a simple object it would be irregular due to slight differences in the cross-sections. The Form Editor has a very useful feature called symmetry that will fix this problem. If you turn on symmetry, whenever you move a point, it's corresponding point(s) will follow and put themselves in the corresponding position. There are five options for symmetry: o None. Every point is completely independent. Default. o Front. The 0 degree points will follow the 180 degree points and vice versa. 90 and 270 are completely independent. o Right. The 90 degree points will follow the 270 degree points and vice versa. 0 and 180 are completely independent. o Both. The 90 degree points will follow the 270 degree points and vice versa. The 0 degree points will follow the 180 degree points and vice versa. Think of it as "oval" symmetry. o 90 Every point will follow the corresponding point in every degree view. Complete radial symmetry. These symmetry options are very easy to use. Note that turning on symmetry does not immediately make the cross sections symmetric- only points you touch and move will change. Most graceful objects have at least one axis of symmetry, many have two, and some have 90 degree symmetry. Note that 90 degree symmetry is actually completely circular. Thus, any swept object (from the Detail editor) can actually be made by using 90 degree symmetry and keeping the radius constant (the top view of the horizontal cross-section). The top view does not have any symmetry controls, and sometimes it would be nice to be able to keep the points somewhat ordered. One way around this is to use "lock" from the select menu. Lock will automatically snap any point you move to the nearest grid location to where you let it go. This is very useful for making straight lines, or for creating symmetric cross sections in the top view. You can also select a bunch of points at once (using the shift key) and use "snap to grid" in the object menu. This makes each point move to the grid location closest to it. You can use the drag box or lasso to help choose what points to select. Grid size is obviously very important when using lock, since it determines the grid intersections. I definitely recommend using grid sizes like 32, 64, and 128. Using 20, 25, 50, 100 certainly seems reasonable until you start dealing with grids like 6.25 or 3.125. The power-of-two grids also work well with zooming, since zoom-in and zoom-out double and halve the screen scale. This is obviously a matter of choice for each user. Some times when dealing with real blueprints or measured objects, different scales are much easier to deal with. There is no question that when you want to build an object in the Forms Editor, you should start simple and work up. Unlike the Detail Editor where adding new (non-modular) details is difficult, adding more polygon resolution is a snap in the Forms Editor. There are actually three modes to the Form Editor. The default is "Edit" which allows you to drag points around to define the cross-sections. However, you can also add new points by selecting "Add" and clicking on CURRENT points. A new point will be added on the line connecting the point you clicked on and one of it's neighbors. You can also position this new point by keeping the mouse button down and dragging the point to its new location. You can edit these new points in Edit mode at any later time. If you add a new radial point (top view) you'll see the point appear at the next (clockwise) segment. If you add a new vertical cross section point, you'll see FOUR points appear, one in each of the four cross section (this is reasonable- the cross sections can't have different numbers of points!) Deletion is done by selecting delete mode and clicking on the unwanted points. Again, 4 points will go away if you select a cross section from the front or right views. It is so simple to add points that defining a new object with a lot of starting points is silly. It is VERY difficult to control that many points, especially in the top view where there you can't use symmetry. It is easier to start off with about 8 points per vertical cross section and around 12 radial sections, and arrange these in a coarse approximation of your object to get general shape and proportions, then add more points for details. Trying to stretch a cross section with a lot of points can be a royal pain. Remember, the plan is to start off with a few points and work up. You'll often find you don't need as many points as you thought to get a well defined object. ------------------ Part III- Examples ------------------ As a final demonstration of how the Form Editor is used, I'll describe three tutorial objects you can make. You are EXTREMELY advised to sit down an make these objects. Reading the tutorial is fine, but moving the mouse around is the best way to learn how to make these sorts of things yourself. There are some screen grabs of some key steps in these tutorials in a file called Form_Tutorial.lzh on hubcap.clemson.edu in the /pub/amiga/incoming/IMAGINE/MISC directory. These screen grabs show the step by step evolution of the examples, as well as a couple of rendered examples. You might want to get these (especially for the last example) but you're welcome to wing it by using the text alone. The file also has a copy of this text in it, so you won't have to separate this mail message out if you're getting it on the mailing list. If you don't know what FTP is, ask a local computer wizard and hope you have access. :-) --------------------------------------------------------------------- A Coke (TM) Can --------------------------------------------------------------------- The Detail Editor has a powerful tool called sweep that can create simple radially symmetric objects like a soda can or a candlestick holder. However, the Forms editor can one-up sweep pretty easily. Our goal is to create an object in the shape of a standard 12 ounce soda can with all the details like the hollow on the bottom and the little metal ridge on the top. The Forms Editor can create objects like this with no trouble, and do it faster and much easier than using the Detail Editor to spin a line outline of the can would take. Enter the Form Editor, and make a new form (in the Object menu) with 4 slices and 20 points. A can at first approximation is just a cylinder. We need many points around the radius to get a nice smooth circle cross-section, but only a few slices to define the rectangular vertical cross-section. For this example, we'll never muck with the 20-point circle cross section. The cylinder is obviously radially symmetric, so we will probably want to turn on 90-degree symmetry from the symmetry pull-down menu. The points that you manipulate in the front and right views will now move their corresponding siblings, keeping the object radially symmetric. To make a quick and dirty cylinder, move each point in the vertical cross sections so that they are on the same Z line- they should stack vertically on top of each other. I like manipulating the right hand cross section in the Front view. Remember, the symmetry mode will move the other three points for you. You can use the perspective view to see what effect you're having on the form. You might look at the screen-grab called can_one to see how the first simple model should look. Again, these screen-grabs have to be downloaded from the FTP site hubcap.clemson.edu. What do we get? Well, our horizontal cross section is unchanged, its still a nice circle. We don't want to muck with it. Our horizontal cross section is a nice straight vertical line. If you think about it, this should give us an object in the form of a tube. If you look at your perspective view and don't see a tube, something is wrong. Look at the can_one picture again to see what the problem is. There are two problems with this tube. First, the sides are a bit wavy, since each point was moved manually and they might not be exactly on the same vertical line. Second, if we really want to make a Coke can, we should at least get the proportions and scale right so we don't have to squash and stretch things later to get it to look reasonable. To fix the wavy line problem, we just use "lock" mode from the select menu. Remember, this will make any point we move jump to grid intersections, so if we move the points around by the same Z line they'll all line up on the same grid line. We should also figure out how to get the right can proportions. If you get out a ruler, you'll find a standard Coke can is 12.2 cm tall and the main body is 3.25 cm in radius. It is difficult to accurately change the radius of our form, but we can make every other measurement use the default radius of 100 Imagine Units as a reference. Hence, there are 3.25 cm in 100 Imagine Units, so the can should be 375 units high. If we change the grid spacing to 25, our can should be fifteen grids high. It is easy to automatically set the height of our object, because the points will leap to the right position when we move them to the correct (coarse) point. You might want to turn on "coordinate" mode from the display menu to help identify where you are moving your points. It might occur to you that we also don't want a tube, we want a solid cylinder, with ends. This is easy to make, we'll just take the top cross section point and move it to the Z axis to enclose the top and move the bottom point to the Z axis to enclose the bottom. This gives us the rectangular cross-section we need to form a cylinder. We'll make our can so that the axis is at the very bottom, at 0, 0, 0, and the can rises to a height of 375 in the Z direction. To actually change our rough tube to this properly proportioned, capped cylinder, set the grid size to 25, turn on lock, and move the top right point in the FRONT view to the 0, 0, 375 grid intersection. The other views should show the corresponding points moving up as well. Move the second point to form the outside top edge of the can, to 100, 0, 375. The third point forms the side, at 100, 0, 0, and the last point will define the bottom, and should go to 0, 0, 0. Your can should look like the picture can_two. Ok, this DOES indeed look like a nice cylinder. So how do we get the nice details like the top rim, and the dent on the bottom, and the narrower "lip ridge" just below the top rim? I said that it was easy to add detail once you had a basic, crude form. Let's make the bottom dent of the can. Turn _off_ lock, so that we can move the points freely to whatever location we want. We want to add come points to the vertical cross sections so we have more control over the shape of the can. Select 'Add' from the mode menu. Now, whenever you click on a point, a new point will appear at the midpoint of the line below it. We want to add a point to the very bottom line segment (Which is currently the horizontal line making the bottom of the can). Just click on the bottom outer point and a new point should appear on the bottom horizontal line. Enter 'Edit' mode from the mode menu, and you'll find this new point is just as easy to manipulate as the originals. To form the bottom dent, we want to move the very last point on our Z centerline UP to make a cavity. The point should be moved about a third of a cm, or 10 units. You might want to turn on 'coordinates' from the display menu to help measure the distance. Once you move the point up, you'll see the dent in the perspective view if you move it so you can view the bottom of the can. The new point that we added can be moved up to make the bottom dent more bowl-like instead of a cone. The trick to adding detail is to identify where you want to add a new feature. If you want to add a new dent or bulge, a new point added at the location you want can be moved in or out to make the feature. If you need to line things up, judicious use of changing the grid size and using 'lock' will let you place the points accurately. Note that the Forms editor LACKS the transformation requester that you find in the Detail Editor, so you can't just type in coordinates for critical points. You have to use grid size and lock to accurately place objects. OK, we know how to add details. Now how do you take the measurements off of the can? There are a few ways- you could judge by eye, you could take a ruler and measure everything, or you can try sneaky tricks. If you fake it by eye, your model is obviously going to be somewhat inaccurate, even if you use a can sitting right next to you as a model. Measuring distances works quite well, though. I used a finely measured rule and a sheet of graph paper to transcribe the shape of all the ridges and bumps. Inputting these coordinates to Imagine involves using the Coordinates display and matching points. However, there is a quick and dirty trick you can use, though this probably isn't applicable to most objects you model. Zoom the front view so that it takes up the whole screen. Center your can in your display by using the "set center" command in the Display menu and clicking at the center of your object. Now, zoom in or out until the size of the outline on your monitor approximates the real size of a Coke can. Take a real can, and press it against your monitor, then eye it. Use the radius as the determining factor, not the height. Now repeatedly use the "set zoom" command from the display menu and muck with the zoom to get the screen can size as close as you can to the real can size when you press it against the monitor. On my 1950 monitor a zoom of 1.05 worked well, but it will vary from monitor to monitor. Once you match sizes, you can actually press the can against the screen with one hand, and move points to match the can outline with the other. [You'll look like a fool if anyone else is around, too!] However silly this seems, I found it the easiest way to input the shape of the can. When I sat with a ruler and some graph paper, my paper diagram turned out to be less accurate as the screen method and took much more time. A rehash on adding the fine details: You have a rough outline. To refine it, just pick the area you want to refine, add a new point on that line, and drag it where you want it. I found that getting a highly accurate cross-section (using 17 points) took less than 3 minutes with the admittedly stupid screen trick. Using a ruler I spent 10 minutes measuring and converting before I even moved the mouse. When you're done, you should have an outline similar to mine, which is shown in the picture can_three. Take a look at your object in the perspective mode with the window zoomed to full screen, and solid display mode on. Rotate the view up and down. Nice, huh? What about the top hole, and the tab? The tab is easy to add in the Detail Editor, by extruding a flat outline. If you expected to make it as an integral part of the can form, I'm sorry to say you were expecting a bit much. The Form Editor likes to make single-piece objects, and you can see how the tab is really a separate part of the can "form." This doesn't prevent you from making a separate tab object and sticking it on, and this is exactly what I did. The hole, on the other hand, is pretty easy to include using the Form Editor! If the hole is facing towards us as if we were going to take a drink, the hole is obviously non-radially symmetric, and it is not front-back symmetric. It IS left-right symmetric. Turn the symmetry from the radial '90-degree' to 'right'. Now, in the FRONT view, move the top point (that is now on the Z axis) straight OUT about a third of the way to the outer radius. This is the WIDTH of the hole on top. In the RIGHT view, move the left-top point (which is the front-top on the can) about 90% of the way to the can rim. Leave the right-top point where it is. The finished can form can be seen in picture can_four. See what we've done? Moving the points away from the center made a hole. We made the front-to-back cross section asymmetric to one side, so the hole location is moved. Look in the perspective view. Play around with moving the hole around and turning symmetry on and off. Why did this make the asymmetric hole? Remember how the form is generated? Each cross-section is interpolated from the 4 defined cross sections. The front cross section blends to the right, which then blends to the back, then to the left, then back to the front. This is very hard to describe, but play with the points and you'll see the kind of control you have. Note that the hole is an oval, which is not quite true for a can. The Forms editor really won't let you do much more unless you want to start mucking with radius modulation, but that's for the next example. This completed can object can object can be loaded into the Detail editor, at which point it becomes a normal object. You can move individual points, apply brush maps, attributes, textures, and manipulate it in any way you would a normal object. After manipulation in the Detail Editor, the objects are generally not reloadable back into the to the Forms editor. Using the Detail editor, you might make and attach the can tab, or move individual points on the top hole to make the ellipse to match a real can's hole more accurately. A final rendered view of a can generated using this tutorial can be seen in the HAM image 'Craftsman', where you can see two separate versions of the can. The carved wood Coke logo was an experiment that turned out well. The Coke logo itself was made with wire cutters, a real can, Digiview, and an hour's touchup in DPaint III. The can could have also been generated in the Detail editor by using the powerful "Sweep" mold function. However, sweep certainly does not provide the interactive updates that the Forms Editor does, and can only make completely symmetric objects. The next examples will show how much more powerful the Form Editor is when it makes very non-lathed objects. --------------------------------------------------------------------- Building a Water Splash --------------------------------------------------------------------- Think of a ball dropping into a pool, and how a corona of water spurts out around it. The splash is vaguely symmetric, and is certainly not a group of primitive cylinders and tori merged together. Building a splash like this using the Forms Editor is obscenely easy, much easier than the Coke can! It is even simple to animate the splash! If we want to make a crude splash model, we should first envision what a cross section of such a splash would look like. The picture splash_one is a 10 second DPaint line drawing of how I see water would splash up and away at the peak of the splash. The center is disturbed but mostly flat, and there is a steep "wall" of water at at certain radius pointing out and up. It curls a bit at the top, with a bulge at the peak, and slopes back IN and down. Outside the wall the water is less disturbed. The wall is the 'shock wave' and is expanding (and falling) with time. It is very, very easy to make a primitive version of this in the forms editor. We pretty obviously want our main axis that our slices are centered around to be vertical. Start a new form, with 30 points and 10 slices, which should give us enough detail to rough something out. Initially, we'll want to make the splash symmetric. Later, we can add asymmetric details, but for now we want the coarse primitive to be radially symmetric, since it will define the basic structure of the form. Use the '90-degree' mode in the Symmetry menu. The initial spherical horizontal cross section is completely useless for our purposes. Pick a height at which you want to base the splash (the bottom point of the cross section is a logical choice) and when you're building the splash, imagine that it is sitting on top of this water. It will give us a good reference point. Pull the top point of the cross section way out and down to the water level. Keep the bottom point in at the center, and also at the water level. The inbetween points should be moved into a crude outline of the sloping water wall that we envisioned. My initial model is shown in the picture splash_two. It took about a minute to build. Look at the perspective view. A bit bland, but it is certainly on the right track. Add a few points to the cross section at the top of the water wave to give it a more complex, bulging appearance. You might want to add some points near the base, especially on the inside, and make the water near the wave a bit more ragged. Now what? Our coarse form was trivial to make, but is far to artificial. Let's jazz it up! Turn OFF symmetry, and muck around with ALL FOUR cross sections. You can increase the height of the wave in one, make the water a little rougher in another, make the peak on one a bit more curved... give them character. DON'T make huge changes like adding a second wave (you're welcome to try!) but certainly make them a bit different from each other. Think of adding a 25% noise level. You might keep an eye on the perspective view, as well- it will show you how the Forms Editor copes with blending these different shapes together. Now what? A little more variation? There's no reason the splash has to be a perfect circle, or even an oval, is there? Of course not. The TOP display shows what the HORIZONTAL cross section of our splash looks like. Right now it's a nice circle. Now, our splash really should be pretty circular when looked from above, but not perfectly... Go ahead and muck with the shape, and again, watch the perspective view to see what happens. You might want to leave SOLID mode on, especially with a fast machine, since the wireframe of such a non-structured object is often very confusing. You can move the radial points any way you like. I suggest that you only move them generally in and out, or the splash will get somewhat lopsided. Also, avoid having sharp spikes. You can see how easy it is to make our splash look like the Statue of Liberty's crown. 2 or 3 point bulges look very nice, major details formed with just 1 point are sharp and look like knives. Not very appropriate for a soft water splash! My final splash is shown in the picture splash_three. A rendered version with three different splashes is called Ocean_Sunset. Ocean_Sunset is actually a still from the current version an anim I'm working on. It has the dolphins jumping around, the water moving with wind-driven waves, and eventually will have a ship slowly steaming along with a nice wake and smoke. The animation of the splashes still need a lot of tweeking, but it's getting better. This is still a work in progress, but it looks nice even now. What about animation? I said it was easy to animate, but how? Well, let's think of what the animation SHOULD look like, then figure how to implement it. How does a splash evolve? The big wall of water starts at the center of the circle and moves outward at a pretty constant speed. It grows in height, curls over, and crashes down as is progresses. If we make maybe 4 or 5 splashes, one for each stage of the splashes growth, we can just move from one to the other. How? Morph! Morph is easy to forget when you're dealing with complex objects like splashes. Since morph requires its objects to have the same structure, different complex objects often won't work with each other. However, if we use the same basic starting form for each of the splashes (same # points and slices) we can have Imagine smoothly interpolate from one form to the next. Considering the fact that creating the splash took maybe 5 minutes, you can see that making an entire animated splash is a 15 minute task. You don't even have to make new splashes, just modify old ones! When animated, you might add frills like separate objects for flying water droplets, and have them follow parabolic arcs. The Form Editor won't let you make detached objects like that, so you'll have to make them as separate objects that fly out, as opposed to pinch off and fly away... You might also use two different splash forms superimposed to give the splash a more complex character. The splash we built is still a bit plain. This example should impress how easy it is to make complex shapes with an amazing amount of speed and control. Asteroid-maker, indeed! --------------------------------------------------------------------- A Complex Boat Hull --------------------------------------------------------------------- Making a boat hull might not seem very easy. If we want to use the Form editor, shouldn't there be some sort of near-radial symmetry? It turns out that you can really push the Forms Editor around in ways Impulse hoped we'd discover. A boat hull is a pretty simple object, right? Well, sorta. If you wanted to build one in the Detail editor, you'd make an outline the shape of an iron (as in for pressing clothes), then you'd extrude it and use slice to make the bottom. Well, this would work, but it's a pretty cheesy boat hull, no matter how good your iron outline was. Even if you were a good modeler, made a series of outlines and used skin to blend them, you are going to get a hull that is boxy as opposed to a nice graceful curve. Think of a big ocean-going vessel, not a cheeseball rowboat. The prow is sharp, to cut into the water, and it angles down and back. The body of the hull is fairly straight, and the stern rounds off smoothly with a flat face as opposed to the prow's sharp point. At no point, however, does the hull look like it was constructed of different sections. To reduce drag, the shape smoothly changes both from the top view (a teardrop with a squashed bottom?) and the side view. It has one axis of symmetry (left/right). How could we ever model this in the Detail Editor? Not easily, and certainly not in one piece. Well, fine. But how could we ever model this in the Forms Editor, either? It certainly is not very obvious. A big hint of how we would design a form for the hull lies in where we place the center, the radial point, of our cross sections. We also have to decide whether the slices should be coming out horizontally (like the axis was a vertical mast) or at right angles. The choice is not obvious. If the axis is horizontal, then the radial sections would tend to form a dome over the hull. If you made the radii of the overhead portion negative (There is no problem doing this!) we could just make a double-thickness of hull. This is messy, but workable. The second option is to use a vertical axis, which gives us the benefit of a simpler object since there is no "dome" to add extra needless points. We want to make a new form object with an XY cross section. Select 3 slices and 7 points and we'll make a very simple version of the hull and work from there. The question is where to but the center of our (vertical) axis. There are three places on the hull where there is a sudden change in cross-section -- the bow, and the two stern corners. If we want to make these changes fairly sudden, we probably want to define each one of them as one of our 4 cross sections. The interpolated cross sections by definition are interpolated, so there's no major change in shape. Thus, we want the bow to be in line with one of the four cross sections, as well as in line with the two stern corners. This makes our choice easy- the only place we can do this is the very back of the boat, along the (port-starboard) centerline. Now that we've decided where to put the axis, how do we want to define the cross sections? Well, we want something that is left-right symmetric, and NOT front-back symmetric, so we should turn on left-right symmetry. We want to change the default nearly-closed spherical cross section to something more resembling an open gravy dish. Move the very top point(s) way out and down some. The front cross section point (the left one in the Right view) should be moved the most. The back cross section point should be moved down, but not out very much. Remember that the stern is very close to the axis, and does not have much detail. The Front view should look somewhat like a big "U", and the Right view should look like a sideways stretched "U" with one end (the bow) sloping back and the other pretty vertical. The horizontal cross section (top view) should look (reasonably) like a boat viewed from above. The front should be pointed, the back should be fairly blunt, but rounding off to the sides. Describing the shape of these forms is harder than describing a Coke can. Look at the picture hull_one to see what my crude shape looks like. You can see in the perspective view that this basic form has a little hull-like character. It is sharp in front, and has a blunt rear. You can add extra points to each of the views to make a smoother form with more details. My final boat hull is shown in picture hull_two. To get an idea of how complex the real object is, there is a picture of the same hull shown in the detail editor in picture hull_three. ----------- The last example is much shorter than the rest, because there is little more to say about the Form Editor. What is does is very complex, but there are few sneaky tricks once you learn how to control the shape of your objects. The best way to become proficient with the forms editor is to practice! I challenge you to build a banana. Or a light bulb WITH threads! [It's quite possible, though annoying]. How about a good pencil object with six sides? This wraps up the tutorial on using the Forms Editor. Sometime in the next month or so I'll be writing a similar (though probably even longer!) tutorial on the using the Detail Editor and another on the general process of object design and creation. -Steve Worley 5/28/91 Because I was erked when my brush and texture tutorials were posted on Compuserve sans credit, I include the following: The text contained within this document as well as the associated computer files are (C) Copyright 1991 by Steven P. Worley. They be distributed freely under the following conditions: 1) The entire text, including this copyright notice, is kept entire and 2) Steven Worley is duly credited as being the author. The author reserves all other rights to this text.