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Quick And Dirty: Making A Lamp With JPatch 0.3

by Mike Kost

Introduction

JPatch 0.3 is a quick and easy spline-based modeler that exports to both Povray and RenderMan. It's written in Java, lightweight and has an easy-to-use material editor. This Quick and Dirty tutorial shows how to quickly leap into JPatch 0.3 by making and rendering a lamp in Povray.

Quick Reading

Here's some reading material as reference and additional information.

Getting and Running JPatch

JPatch can be downloaded from Sourceforge here. When it's unzipped or untarred, the jpatch.jar is in the newly created subdirectory.

To execute JPatch, you need a Java Runtime Environment version 1.4 or later. If you're lacking this, Sun Microsystems will be happy to provide it.

Once you have both available, start JPatch with 'java -jar jpatch.jar'

First Look

On startup, you're presented with a basic window. The tool bar across the left from top to bottom handles model manipulation. The tool bar across the top from left to right is used to change views of the model. For this Quick and Dirty, we'll mostly be interested in the tool bar icons below.

Toolbar Icons	Function
	Add point
	Lathe
	Snap to grid

Quick Configurations

When working with JPatch, there's a few things I like to do in preparation for working on a project:

I enable Snap to Grid by clicking on the "Snap to grid" icon. This prevents points from getting off grid and getting sloppy before I intend them to.
I adjust my grid spacing value down to something more like "0.1". This is done through the menu selection Options->Set Grid Spacing. I like to think of my objects in units like feet or meters so using minor grid steps of 1 foot or 1 meter becomes annoying. You can zoom by placing your mouse cursor over the grid area and using the mouse scroll wheel to zoom in (up) and zoom out (down).

Putting Down The First Line Segments

To begin, we need to put down 3 points. To place the first line segment: click the "Add point" icon, left-click and hold where you wish the line segment to begin, and drag the mouse and release to where you'd like the line segment to end. If you've enabled snapping to grid, the cursor will want to head toward a grid point. For the purposes of this tutorial, the line segment should be close to the Y-axis (noted in the lower left corner by the vertical green line). After the first line segment is added, add 2 more with the new line segments picking up where the old one ended.

Lampshade Lathe

The next step is to perform a lathe operation on the line segments we just added. To do this, select the 3 line segments by left-clicking and dragging to create a box around the 3 line segments. After the line segments are selected, click the "Lathe" icon. Select the default number in the popup dialog box. The lathe operation rotates the structure we just made around the Y-axis and is very similar in principle to the Povray lathe object. To get an idea of how the object has been transformed, right click on the grid area and select views->Top view. If you need a better view of our new lamp shade, middle-click and hold to move the grid around. Repeat the process selecting views->Front view when to get back to where we started.

Base Lathe

The next step is to create the lamp base. Using the Add point icon, construct a base. Because the lamp shade is in the way, it is much more difficult to select all the points for a lathe operation. Instead, click on the points in the base individually while holding down the CTRL key. After selecting all the points in the lamp base, click the "Lathe" icon. When prompted, enter "128" for the number of segments. The segments determine the number of steps that will be used to create the resulting lathe structure. For the lamp shade, we used the default, 8 segments. As you notice after the lathe is finished, the base has a much more detailed modeling because more segments were used.

Generating Patches

After everything is done, press F5. This causes JPatch to compute all the various patches that make up our new lamp. To see the result, right-click on the grid area and select show->patches. You'll notice that the lamp fills in. Every time you make additions, deletions, or changes to the model, you need to recompute the patches.

Materials

After all that work, we still only have a gray lamp. To change colors, we need to do some material editing. Under the Materials tree, select the Default Material and click edit. This will bring up the JPatch material editor. Here you can play with various color and finish combinations to find a material that works for your needs. In this case, I want a black lamp base and have altered red, green, and blue accordingly. Clicking OK closes the material editor and saves the changes.

Since I want the lamp shade to be a different color, I select the Materials entry in the tree and click "New Material". This creates a new material called New Material. I want a red lampshade and I alter the New Material to make it red using the procedure mentioned above. To apply the New Material to my lampshade, click on the "lathe #1" tree element. This selects the lampshade. Now click on the New Material tree element and click Apply. The lampshade is now red.

Rendering

To render our new lamp, choose File->Export. When you choose a file name, this object will export as a Povray include file. I exported it as "object.inc". To give povray a source, I used the default Povray source included with JPatch, altered to read in my lamp and move the camera slightly.

camera {
    angle 50
    location <0,15,-50>
    look_at <0,5,0>
}

background {
    color rgb <0.5,0.5,1.0>
}

light_source { <-1000,1000,-1000> color rgb 0.66 parallel }
light_source { <1000,0,-1000> color rgb 0.33 parallel }
light_source { <0,1000,1000> color rgb 1.0 parallel }

#include "object.inc"

You can get my example files here: example_scene.pov, object.inc.zip

The final rendering was done by 'povray +P +W320 +H240 example_scene.pov'.