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3.1 Object Types

3.1.1 Primitives

There are 3 basic geometric primitives available in Art of Illusion: cube, sphere and cylinder objects, which can either be created using the modelling tool icons in the upper left corner of the screen or via the top menu bar as follows:

Using the modelling tool icons allows immediate creation of the primitive. Simply click on the relevant icon:

cube: sphere: cylinder:

then click and drag on any viewport to define two of its initial dimensions. The 3rd dimension will have to be altered if necessary using the scaling tool in one of the other viewports. Alternatively, holding shift while dragging forces all 3 dimensions to be equal.

For cylinders, the top:bottom ratio can be set to form tapered cylinders (including cones) prior to drawing by double-clicking on the cylinder icon. This ratio can also be edited after drawing (see editing_objects). Creating the primitive via the menu bar is achieved by selecting Object -> Create Primitive and then selecting the appropriate shape. Cones can also be created directly using this method. This method brings up a dialogue box similar to that on the left which allows the exact size, position and orientation of the object to be specified.
Primitives have limited use for creating realistic objects as such objects are rarely that simple in real life. However they can be useful for cartoon-like scenes or for building up more complex models using Constructive Solid Geometry (CSG) via the Boolean tool like in the simple example on the right:

Primitives are also important as they can be the starting points for creating triangle meshes. See 3.1.4 below.

There is one other important primitive object: the Null object. Null objects do not show up on renders as they have no geometry. Their main use in is grouping other geometrical objects together. For example you might want to create a car out of a set of geometric objects representing the car body, wheels, windscreens etc. A neat way to keep all the parts together would be to create a Null object and to group the geometric objects as children of that Null (see the Object List for more details). Nulls are represented as crosses in the viewports.


3.1.2 Curves

These are one dimensional objects and thus are of no direct use. However, they can be used in a variety of ways to create 3-D objects.

Curves are created by defining a series of points in any of the viewports. They can have one of two types of smoothing: 'Interpolating', for which the curve is forced to pass through the points and 'Approximating' where the curve does not have to pass through all the points but is still controlled by them.

To create an interpolating curve, click on

Then click a series of locations on a viewport to define the points as shown on the right:

To define the last point on the curve and thus end curve point definition, double click. If you wish to automatically close the curve, press <ctrl> and double click. Alternatively to end the curve without adding more points, press Enter to end without closing or <ctrl> Enter to close the curve.

Approximating curves are created in the same way but using the icon.

Closed curves can also be filled to create 2D objects by converting them to triangle meshes.

Another way to create a curve is to use the polygon tool. A polygon is any flat shape with 3 or more sides. To create a polygon curve, double click on which brings up this dialogue box:
You can specify how many sides the polygon has and the type of smoothing of the edges. Selecting 'angled' gives the polygon straight edges, while choosing either 'interpolating' or 'approximating' creates rounded edges. Because 'approximating' smoothing does not require the curve to pass through all the points, this results in a smaller overall shape for the 'approximating' polygon.
The figure on the right shows the differences between the 3 types of smoothing for a 3-sided polygon curve:

These were created by clicking once on the polygon tool icon and dragging a rectangular area on one of the viewports to define its size.

Note: The Polygon tool can also be used to create 'filled polygon surfaces' which are triangle mesh objects. This is achieved by holding <ctrl> while dragging.


Editing Curves

Once polygon edges or curves have been created, the points defining them can be edited by double-clicking on them in the Object List. For example, double-clicking on the interpolated 3-sided polygon displays the editing window below:

Points are selected and deselected using the Select/Move tool. Multiple points can be selected by pressing <shift> before clicking on each point. Points can also be selected using a marquee method by dragging a rectangular box over a group of points. <Shift> selects works for the marquee selection also. All points can be selected using the appropriate option from the Edit menu.

To deselect points, simply click or <shift> click on them. Alternatively a group of points can be deselected by pressing <ctrl> and dragging a rectangle over the required points.

Selected points can be moved using the Select/Move tool or rotated, skewed, scaled and tapered with the appropriate tools shown on the left. Most of the tools activated from these icons are self-explanatory. Resting the cursor over the icons will bring up a tooltip to describe its function. The operation of most can be modified by pressing <shift> or <ctrl> - see the bottom of the editing window for details relevant to each tool.In general, handles around the selected point(s) can be dragged to effect the operation. Pressing <shift> while dragging causes the operation to be a uniform one, whilst <ctrl> centres it. The spacebar can be used to switch between tools quickly; pressing it toggles between the Select/Move tool and the last tool used.

The view in the curve editor is controlled as in the main view windows, i.e. yhrough use of the camera move/rotate icons or the keyboard shortcuts. See here for more details.
Additional editing is possible through the top menu bar.


This is the Edit Menu:
Undo/Redo - undoes the last action or redoes something you have just undone, including selections.

Select All - selects all points in curve.

Extend Selection - automatically selects adjacent points to those already selected.

Invert Selection - deselects all currently selected points and selects all currently deselected points.
Freehand Selection - enters a selection mode that allows you to trace a freehand path - all points enclosed by the path are selected. This mode can be toggled on/off.
Curve Tension - This controls the amount by which adjacent points (and possibly beyond) move with currently selected points. Selecting this option produces the dialogue box on the right. The Maximum Distance is the number of points each side of the currently selected point that are affected. The Tension is strength of the attractive effect so that a 'very high' tension will move the affaected points significantly whereas a 'very low' tension will move them only a little.

The Curve Menu looks like this:
Delete Selected Points - deletes all selected points !

Subdivide Selection - A way of adding points to an existing curve, this tool adds a point between each pair of currently selected points.

Edit Points - Allows you to explicitly define the coordinates of any point or group of points. A realtime preview of the effect of values entered in the dialogue is shown on the actual curve - cancelling the dialogue causes the curve to revert back to its original shape.

Randomise Points - translate points by a random number below a user-specified maximum in any or all 3 axes.

Transform Points - brings up the dialogue on the right to allow points to be moved, scaled or rotated accurately. Can also transform about centre of selection or origin of object.


Centre Curve - moves the curve object so that its centre coincides with the origin (0,0,0).


Set Smoothness - If either interpolating or approximating smoothing is used, it is possible to specify the smoothness of individual points. In the example on the right, a heart shape was created with the approximating curve tool. To 'sharpen' the curve in the right places, the points shown were selected and their Smoothness set to 0. This makes them completely sharp but values between 0 and 1 can be used to obtain intermediate smoothnesses. A realtime preview of the effect of smoothness values entered in the dialogue is shown on the actual curve - cancelling the dialogue causes the curve to revert back to its original shape.

Smoothing Method - This is the method used to smooth the curve. The choices are None (straight lines between points), Interpolating or Approximating.

Open Ends - if the curve is closed, i.e. a complete loop, this will break it and vice versa.

The View Menu looks like this:

Display Mode is irrelevant for curve objects.

Show allows the editor to view the Curve or the Entire Scene for the currently highlighted window. Only the curve,however, can be edited.

Coordinate System can either be Local or Scene. In the former case, all objects are displayed in a coordinate system that has the curve at the origin. The latter option displays objects as they are in the main view.

One View/Four Views toggles between having the four view display or a one view display of the currently selected window

Grids allows a grid to be visualised and snapped to. See here for more details.

Show/Hide Coordinate Axes toggles display of the x,y and z axes as shown here.

Show/Hide Template displays or hides the image selected as the background in the next menu option.

Set Template Image... allows an image (in .jpg, .png or .gif format) to be used as the background in the editor. This is useful as a reference when modelling. Selecting this displays a dialogue to allow selection of the image which can then be turned on/off with the previous menu entry.







3.1.3 Spline Meshes

Splines are smooth surfaces the shape of which are determined by control points and the type of smoothing applied. Splines can be created by applying the various modelling_tools to existing objects (usually curves) or directly by clicking on
Before doing that, you can select some of the spline properties by double-clicking on that same icon. This brings up the dialogue box on the right:


The U and V size boxes determine the physical dimensions of the spline mesh 'sheet', i.e the number of control points in each of the two dimensions.


The shape can be either flat, a cylinder or a torus. In the latter 2 cases, to understand the U and V dimensions it may help to think of a rolled-up sheet. For a cylinder, U-size is the number of points around the circumference and V-size is the number of points along its axis. Similarly for a torus, U is along the circumference and V-size is the number of points around the cross-section.


The smoothing method can be either 'approximating' or 'interpolating'. See 3.1.2 for an explanation of these terms.


The Thickness parameter is only relevant for the torus and controls the cross-sectional diameter as shown on the right.


Once the spline has been created, it can be edited by double-clicking on the object in the Object List. This brings up an editing window similar to this:

As in the main viewports, the orientation, scaling and type (parallel or perspective) of view can be controlled using the familiar camera control icons/keyboard shortcuts and drop down menus at the top of the view. The type of shading can also be altered by selecting Mesh -> Display Mode (see Display Mode for details on this)

The editing utility allows both vertices ('points') or curves to be edited. The editing mode is selected by clicking on the appropriate button at bottom left. The icons on the left allow points and curves to be transformed in various ways as identified on the diagram above. The points or curves to be transformed must be selected first using the move/select tool. Activating this tool by clicking on the icon allows selection of individual points or curves by simply clicking on them. Multiple selections are achieved by holding down <shift> while successively clicking on further points/curves. A marquee ('rubber band') selection is also possible and is performed by dragging the mouse while holding the left mouse button to highlight a rectangle. Note that for curves, you need to enclose the whole curve within the selection marquee for this to work. Pressing <ctrl> while clicking or dragging a marquee de-selects all currently selected points/curves.

Most of the tools activated from the icons are self-explanatory. Resting the cursor over the icons will bring up a tooltip to describe its function. The operation of most can be modified by pressing <shift> or <ctrl> - see the bottom of the editing window for details relevant to each tool. The tools available are a subset of those for triangle meshes; see here for more details. The spacebar can be used to switch between tools quickly; pressing it toggles between the Select/Move tool and the last tool used.

Skeletons are discussed in detail in Section 3.1.5.

MENUS

Further useful tools are found on the top menu bar:


The Edit menu looks like this:

Undo/Redo - undoes the last action or redoes something you have just undone, including selections.

Select All - selects all points or curves.

Extend Selection - expands selection by adding points/curves adjacent to those currently selected.

Freehand Selection - enters a selection mode that allows you to trace a freehand path - all points or curves enclosed by the path are selected. This mode can be toggled on/off.
Mesh Tension - introduces a neighbour attraction effect so that moving a point/curve also results in (lesser) movement in the points/curves adjacent to it. The mesh tension dialogue box is shown on the right.

The Maximum Distance defines the number of points affected. For example setting this to 2 means that vertices within 2 points along all edges of the mesh will undergo some transformation the magnitude of which decreases with distance from the selected point. The example on the far right illustrates this. The pink point is the selected vertex; the green points are those that would be affected if Maximum Distance was set to 2.

The Tension defines the strength of the attractive effect so that a 'very high' tension will move adjacent points significantly whereas a 'very low' tension will move them only a little.



The Mesh menu is shown below. Note that some items on this menu will not be available depending on which mode you are working in. These are the options available in curve editing mode. Delete Selected Curves - deletes all selected curves

Subdivide Selection - this only works on a set of adjacent curves and creates a new curve between each adjacent curve as shown below. This can help produce a smoother finish and in adding small details to a mesh.



Edit Points allows you to specify absolute x, y and z co-ordinates for selected points and to specify skeleton properties (see Skeletons). A realtime preview of the effect of values entered in the dialogue is shown on the actual mesh - cancelling the dialogue causes the mesh to revert back to its original shape.


Transform Points allows you to move, rotate and scale selected points/curves by explicitly entering the values in the x, y and z axes.

Randomise Points causes random variations in position within a user-defined tolerance. This is useful, for example, in simulating imperfections found in real life.

Texture Parameters is discussed in detail in textures_and_materials

Centre Mesh translates the mesh so that its centre lies at (0,0,0).

Extract Selected Curve creates a copy of the currently selected curve as a new object. Only works if a single curve is selected.

Set Smoothness allows you to define how sharp the mesh is at the selected points/curves. In the example below, the smoothness of 3 of the curves was changed from 1 to 0 on the right hand image, causing sharp creases. A realtime preview of the effect of smoothness values entered in the dialogue is shown on the actual mesh - cancelling the dialogue causes the mesh to revert back to its original shape.


Smoothing method is either interpolating or approximating. Both are a type of subdivision to create smooth surfaces from a mesh of control points.

Closed determines which of the spline curves is closed, i.e. a complete loop. This can be set to U only, V only, both or neither. In the example above, the U curves are closed forming a circular cross-section for the bowl.

Invert Surface Normals - in some circumstances faces do not display correctly as the surface normals have become flipped. This remedies the problem.

Render Preview - produces a raytraced render of the mesh so that you can check that everything is going to look as it should in the final render.


The View menu is like this:

Display Mode - switches between wireframe, shaded, smooth or transparent display for the currently highlighted view, as in the main window.

The Show submenu allows various items to be displayed or hidden on the view.
See the section on triangle meshes for more details.


Coordinate System - Here you can choose to work with the mesh in its Local coordinate system or in the Scene coordinate system. This will affect the orientation and position of the mesh.

Grids - As in the main window, Grids can be shown and, if necessary, used to snap objects to.

Show/Hide Coordinate Axes toggles display of the x,y and z axes as shown here.

Show/Hide Template displays or hides the image selected as the background in the next menu option.

Set Template Image... allows an image (in .jpg, .png or .gif format) to be used as the background in the editor. This is useful as a reference when modelling. Selecting this displays a dialogue to allow selection of the image which can then be turned on/off with the previous menu entry.


The Skeleton menu is described in detail in Section 3.1.5.

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