Basic tutorial #3:

Modelling a screwdriver using CSG

written by Olivier SARAJA

e-mail: olivier@linuxgraphic.org

In this tutorial, we will see how to model a screwdriver using CSG (Constructive Solid Geometry). The process is quite straightforward, and uses Boolean logics. This mean rigor and basic knowledge in order to get the proper result. Fortunately, the Object Tree will help us getting the right result. But here we go for a little explanation on Boolean operations first.

A few words on the Boolean operations

Kpovmodeler make use of four kind of Boolean operations during the modeling stage. Union, Intersection, Difference and Merge. Let's study how these operands work when two (or more!) overlaping volumes are involved:

Union and Merge:

These two cases seem to behave the same way: the two objects look as glued altogether (as on the previous picture that involves no Boolean). But in fact, there are slight differences between the two results, that can be easily seen if you give the same texture -with some transparency- to the two objects (let's say a Pigment Solid Color with a Filter value set to around 0.4).

In fact, Union merely glues two objects altogether and keeps the frontiers of each, while Merge considers only the frontier of the overall object. This is why the overlap volume of the two objects is showed on the Union picture, and not on the Merge picture. As a first thought, the difference between Union and Merge becomes relevant only when you deal with transparent materials.

A common question could be « Why should I bother using Union or Merge when I could get the same look on my rendering without using any CSG? » Let's face it, you're certainly right: upon rendering (unless you make use of semi-transparent materials) you won't see a difference. It's more in the way you deal with objects after a Merge or Union operation that you'd find a difference. When multiple objects are involved, you can rotate, translate, resize, assign a material and much more to all the involved objects at once if you used Boolean first. If you didn't, then you'll have to apply all the transformations on a one-for-one basis for EACH object involved! But hey, it's your time and your business!

Intersection:

The result of an Intersection operation is quite easy to understand: The resulting volume is equal to the overlaping volume of the two objects.

Difference:

The order in which the objects are described in the Object Tree (reading from top to bottom) particularly matters in this case: Box then Sphere reads as a boolean « substract Sphere volume from the Box volume » operation. Of course, Sphere then Box reads as a boolean « substract Box volume from the Sphere volume » operation.

Step 1: Loading the default scene

First of all, open kpovmodeler and load the basic scene. I configured this scene with some basics that will let us concentrate on the modelling of the screwdriver: a basic plane for the ground, two light sources (one coming from the virtual ceiling and another coming from a virtual window) and a camera. I also configured the global settings, even if I kept all the default values: it can later become interesting to play with these values for a greater impact upon rendering, but it is beyond the scope of this tutorial.

This is the basic scene I always use when I model objects: all the attention is focused on the object, not on the scene. It's perfect for a library of ready-to-use objects, such as these I modeled recently:

Please click on this link to save the default.kpm file in a proper place of your hard disk. Once done, you can upload it into kpovmodeler (File > Open or Icon) then browse to the file location and click on the OK button.

You are suggested to immediately save this file with another file name (File > Save As...):

type the new filename (screwdriver.kpm, for example) in the 'Location' field and press the Save button to generate the file.

Step 2: Setting a few good primitives (long)

Let's go! First of all, select the 'Scene' entry in the Object tree. All subsequent objects created will be added as children objects. Add a cylinder to the scene (Insert > Finite Solid Primitives > Cylinder or Icon). You will be prompted to choose weither the object should be inserted as a First Child or Last Child object in the Object tree. Please choose Last Child. This way, all the lines regarding the object you're currently modeling will be located at the bottom of the Object tree.

Click on the '+' symbol standing just before the name of the new line to develop all the already available properties.

Each newly inserted object comes with these three properties: scale, rotate, translate. When they are not immediately available you can add them to the object by clicking on the object's line in the Object tree and then:

Using the menu: Insert > Transformations > Scale, Rotate and/or Translate

Using the toolbar: click on the , or Icons

For the Finite Solid Primitives, it souldn't be necessary, so you can directly click on the existing rotate entry in the Object Properties View and adjust parameters as follow (don't forget to press the Apply button or to hit Enter):

rotate

x = 0, y = 0, z = 90

The same way, click on the resize entry and adjust the parameters as follow:

scale

x = 1, y = 8, z = 1

Eventually, click on the Cylinder entry and set the parameters as follow and uncheck the Hollow box:

cylinder

End 1: x = 0, y = 0.5, z = 0

End 2: x = 0, y = -0.5, z = 0

Let's create a sphere for one of the ends of the cylinder (Insert > Finite Solid Primitives > Sphere or Icon).

Please note that the Sphere has automatically inserted as Last Child object in the Object Tree, because the selected entry was the Cylinder and that it can't afford a Finite Solid Primitive entry as a Child. Now click on the Sphere entry and set the parameters as follow and uncheck the Hollow box:

sphere

Center: x = -4, y = 0, z = 0

Radius: 0.15

Of course, the sphere will later be merged with the cylinder. With the same logic, we will add two Box objects that will be substracted to the merged group object in order to make the blade of the screwdriver.

First add a new Box object to the scene (Insert > Finite Solid Primitives > Box or Icon).

Click on the '+' symbol standing just before the name of the new line to develop all the properties of the Box object. The same way we already did with the Cylinder and Sphere objects, adjust the following parameters as follow and uncheck the Hollow box:

box

Corner 1: x = -0.5, y = -0.25, z = -0.25

Corner 2: x = 0.5, y = 0.25, z = 0.25

rotate

x = 0, y = 0, z = -13

translate

x = 3.7, y = 0.35, z = 0

And now, for the tricky part: we will duplicate the Upper Box and turn the copy into a Lower Box. Fortunately, the Object tree will help us keeping this operation simple. Here is what we currently have in the Object tree, and what we would like to see, the Lower Box being the symetrical along the x axis of the Upper Box:

Here's how we can get this result. First of all, select the Upper Box entry in the Object tree. Make a copy of this entry (Edit > Copy or CTRL+C or Icon) and then paste it (Edit > Paste or CTRL+V or Icon). With the new entry selected, immediately change its name in the Object Properties View, and then change its rotate and translate values according to the following values:

rotate

x = 0, y = 0, z = 13

translate

x = 3.7, y = -0.35, z = 0

Step 3: Using CSG for the Blade

The nasty job is already done, and here comes the meaningful and simplest one: using the Object tree, we will sort the different primitives we just inserted and call upon Boolean operations in order to get the proper shape for the blade of the screwdriver.

With the Scene entry selected, please insert a Union, a Merge and a Difference object (Insert > Constructive Solid Geometry > Union, Difference and Merge or , and Icons).

Each time, you'll have to declare the new object a Last Child upon popup request. Here's what you should get in the Object tree:

Using Drag&Drop, CTRL+X (Cut) and CTRL+V (Paste) or the Cut and Paste icons, sort the entries of the Object tree in order to get the following result (choose First Child or Last Child as appropriate):

The Union entry will be useful later, when we will start to model the shaft of the screwdriver. In the Object Properties View, the Difference entry could be renamed something like Screwdriver Blade, for an improved visibility in the Object tree.

Step 4: Setting a material for the Blade

Of course, rendering the scene now will show us nothing but a pitch black blade for the screwdriver: we need to define a proper material. There are many way to set a material, but I'd like to introduce a method that make the material easily reusable in another scene. Of course, you could reuse one of the Chrome textures shipped with the kpovmodeler example files but I thought it would be more interesting to set all the following by ourselves.

Select the Scene entry in the Object tree, then insert a Declaration as a Last Child (Insert > Declaration or Icon).

In the Object Properties View, you can rename it to Chrome. Then Insert a Texture (Insert > Textures > Texture or Icon), a Pigment (Insert > Textures > Pigment or Icon) and a Solid Color (Insert > Textures > Solid Color or Icon). Click on the Solid Color entry and modify the parameters as follow:

solid color

red = 0.93333, y = 0.93333 , z = 0.93333

filter = 0, transmit = 0

Now select the Texture entry, Insert a Finish (Insert > Textures > Finish or Icon) and adjust the parameters as follow:

The texture has been correctly set, but you still have to assign it to the Screwdriver Blade. In order to do this, first move the Texture Declaration just after the T_Grnt16 already showing in the Object tree. By doing this, you make sure that all the objects declared 'later' in the tree can use this texture as part of its own texture declaration.

Select the Screwdriver Blade, and insert a texture (Insert > Textures > Texture or Icon) as Last Child. Click on the Select button and then choose 'Chrome' in the popup list.

And here's the final result:

Quite easy, huh? In fact, you'll see that modeling the shaft of the screwdriver is equally easy and straightforward.

Step 5: Modeling the shaft

You should be used to CSG for modeling, now, so we'll try to get to the result more quickly and with less speech than previously: you already have all the basics at hand, it's up to you to improve your skill with them!

First of all, with the Scene entry selected, let's add a Cylinder (Insert > Finite Solid Primitives > Cylinder or Icon) as Last Child. Keep all the Object properties for the Cylinder by default, but adjust the following parameters:

rotate

x = 0, y = 0, z = 90

translate

x = -5, y = 0, z = 0

The Hollow box should be unchecked. With the Cylinder entry selected, you can add now a Sphere (Insert > Finite Solid Primitives > Sphere or Icon) after having selected the Cylinder entry: the Sphere appears immediately after the Cylinder in the Object tree. In the Object Properties View for the Sphere, adjust the following parameters:

Center

x = -8, y = 0, z = 0

Again, the Hollow box should be unchecked. With the Sphere selected in the Object tree, we will insert a Torus, because it is a Finite Solid Primitive we never used to this day (Insert > Finite Solid Primitives > Torus or Icon) and that will add some fun to the process.

Torus

Minor radius: 0.25

Major radius: 0.6

rotate

x = 0, y = 0, z = 90

translate

x = -2.5, y = 0, z = 0

Finally, with the Torus selected, we can insert a Box object (Insert > Finite Solid Primitives > Box or Icon) and adjust its parameters as follow (uncheck the Hollow box):

Upper Box

Corner 1: x = -9, y = 0.4, z = -1

Corner 2: x = -1.5, y = 0.6, z = 1

Duplicate it three times the same we did in Step 2. Rename respectively the boxes Upper Box, Lower Box, Left Box and Right Box and change the Object Properties as follow:

Lower Box

Corner 1: x = -9, y = -0.4, z = -1

Corner 2: x = -1.5, y = -0.6, z = 1

Left Box

Corner 1: x = -9, y = -1, z = 0.4

Corner 2: x = -1.5, y = 1, z = 0.6

Right Box

Corner 1: x = -9, y = -1, z = -0.4

Corner 2: x = -1.5, y = 1, z = -0.6

That's it! All the primitives are set, let the magic of the CSG operates!

Step 6: Using CSG for the Shaft

With the Scene entry selected, please insert a Merge and a Difference object (Insert > Constructive Solid Geometry > Difference and Merge or and Icons) as Last Child. You should have something like this in your Object tree:

As we already did in Step 3, using Drag&Drop, CTRL+X (Cut) and CTRL+V (Paste) or the Cut and Paste icons, sort the entries of the Object tree in order to get the following result (choose First Child or Last Child as appropriate):

Please note that the Blade and the Shaft of the screwdriver have been both moved in the Union entry we inserted during Step 3. You can rename the difference entry 'Screwdriver Shaft' and the union entry 'Screwdriver'. All the modelings are now over, but we still have to set a proper texture for the Shaft.

Step 7: Setting a material for the Shaft

Select the Scene entry in the Object tree, then insert a Declaration as a Last Child (Insert > Declaration or Icon).

solid color

red = 0.98039, y = 0.94902 , z = 0.05490

filter = 0.45, transmit = 0.2

Now select the Texture entry, Insert a Finish (Insert > Textures > Finish or Icon) and adjust the parameters as follow:

The texture has been correctly set, but you still have to assign it to the Screwdriver Shaft. In order to do this, first move the Texture Declaration just after the Chrome declaration previously set in the Object tree.

Select the Screwdriver Shaft, and insert a texture (Insert > Textures > Texture or Icon) as Last Child. Click on the Select button and then choose 'Plastic' in the popup list.

And here's the final result:

Conclusion

Here we are, at last. Our brand new screwdriver is almost ready to use in another scene. To make things easy, you would like to select the Screwdriver entry, and insert transformations properties (Insert > Transformations > Scale, Rotate and/or Translate, or , and Icons). Importing this object in another scene is quite easy and straightforward: you need to have the source file and the destination file both open in kpovmodeler. In the source file (screwdriver.kpm, for instance), select the Screwdriver, Chrome and Plastic entries. You can then copy and paste them in the destination file (yourscene.kpm, for example). In fact, you can copy and paste any object of the Object tree from a source file to another. This means that you can easily import textures, lighting conditions, camera and so on. Have a good time!