Generating pen plotter art

A pen plotter is a computer output device that can draw with a pen (or a brush, marker, etc) on a paper. Some such devices move the pen in the X and Y axes, while others can move the paper instead.

Pen plotters were introduced in the 1950s and 60s and have become popular among artists since the mid 2000s.

Unlike other output devices like ink-jet and laser printers which accept pixels, pen plotters must be fed with vector data: lines and curves.

OPENRNDR provides a rich toolset to generate and manipulate vector data.

SVG vs g-code

There are two main file formats used to send designs to pen plotters:

• SVG (Scalable Vector Graphics), used with newer devices like the AxiDraw.
• g-code, often supported by older plotters, CNC devices and laser cutters.

OPENRNDR can easily load, manipulate, generate and save SVG files. There is a non-yet-merged contribution to add g-code support.

The following sections focus on SVG.

Hello world

This is one of the simplest programs we can write to produce an SVG file containing just a circle.

fun main() = application {
    program {
        val design = drawComposition {
            circle(drawer.bounds.center, 200.0)
        }
        design.saveToFile(File("data/design.svg"))
    }
}

The API in the composition drawer is almost identical to the one of the standard drawer: we can use methods like segment, contour, shape, circle, rectangle, etc.

Note: if you are using OPENRNDR / ORX version 0.4.5 you need to enable orx-composition and orx-svg in the build.gradle.kts file.

Interaction

Lets take our simple program a step further and make it interactive. We will generate a new design every time the mouse is clicked and save the design when we press the s key on the keyboard.

fun main() = application {
    program {
        // Create an empty composition
        val design = drawComposition {}
        
        // A function to draw concentric circles into the composition.
        fun generateDesign() {
            design.clear()
            val separation = 4.0
            val steps = (drawer.bounds.center.distanceTo(mouse.position) / separation).toInt()
            design.draw {
                repeat(steps) {
                    circle(drawer.bounds.center, (it + 1) * separation)
                }
            }
        }
        
        // Draw the composition onto the window
        extend {
            drawer.clear(ColorRGBa.WHITE)
            drawer.fill = null
            drawer.composition(design)
        }
        
        // Generate a new design every time we click the mouse
        mouse.buttonDown.listen {
            generateDesign()
        }
        
        // Show a save dialog when pressing the `s` key, then save the design
        // with the chosen file name into the selected folder.
        keyboard.keyDown.listen {
            if (it.name == "s") {
                saveFileDialog(supportedExtensions = listOf("SVG" to listOf("svg"))) { file ->
                    design.saveToFile(file)
                }
            }
        }
    }
}

With the last program we could create minimal designs by clicking the mouse button on different locations on the program window and then save the design when pressing the s key.

If we open the resulting design in Inkscape we will notice that the document size is 640 pixels wide and 480 pixels height, matching the default OPENRNDR window size. In Inkscape we could choose a different document size (A4 for instance) then re-center and scale the design to match our preferences.

Lets find out how to specify the SVG document dimensions, and how to make what we see in the window match what gets exported as SVG. (Coming soon…)

Find more tips on using OPENRNDR with pen plotters in the forum.

edit on GitHub