I had a Kotlin microservice that needed to produce a simple heatmap chart on an HTML page to a large audience very rapidly. This was an ad hoc DevOps requirement, so I didn't want to take on an involved Javascript solution. Instead, I went with spitting out a half page of inline SVG text generated by the server itself. This DSL made the server code trivial and has easily met the performance needs.
fun codeMonkey() {
val svg = SVG.svg(true) {
height = "300"
width = "300"
style {
body = """
svg .black-stroke { stroke: black; stroke-width: 2; }
svg .fur-color { fill: white; }
""".trimIndent()
}
// Label
text {
x = "40"
y = "50"
body = "#CODE"
fontFamily = "monospace"
fontSize = "40px"
}
// Ears - example using a function because USE tag doesn't work in Safari
ear(100, 100)
ear(240, 70)
// Face
circle {
cssClass = "black-stroke"
id = "face"
cx = "180"
cy = "140"
r = "80"
fill = "#aa450f"
}
// Eyes
circle {
cssClass = "black-stroke fur-color"
id = "eye"
cx = "160"
cy = "95"
r = "20"
}
use {
x = "45"
y = "-5"
href = "#eye"
}
// Muzzle
circle {
cssClass = "black-stroke fur-color"
cx = "195"
cy = "178"
r = "65"
}
// Nostrils
circle {
id = "nostril"
cx = "178"
cy = "138"
r = "4"
fill = "black"
}
use {
x = "35"
y = "-5"
href = "#nostril"
}
// Mouth
path {
cssClass = "black-stroke"
d = "M 150 150 C 100,250 305,260 230,140 C 205,190 165,170 150,150 Z"
fill = "red"
}
}
FileWriter("build/tmp/codeMonkey.svg").use {
svg.render(it, SVG.RenderMode.FILE)
}
}
private fun Container.ear(x: Int, y: Int) {
circle {
cssClass = "black-stroke fur-color"
cx = x.toString()
cy = y.toString()
r = "40"
}
circle {
cssClass = "black-stroke fur-color"
cx = x.toString()
cy = y.toString()
r = "28"
}
}
Yields a code monkey:
Originally the attribute values were appropriate types, but eventually as support for percentage values etc. was
added, and considering they are always represented as strings in SVG, the value type was changed to String. But that
made errors like length = "foo" possible. Therefore, attribute validation was added. Over time other validations
became apparent too. With validation on, while the SVG is created, things are checked, for example when an attribute
string is assigned, if it can be properly validated, it is. Validation can be turned off for performance reasons.
SVG is an XML tag based format. Those tags can be put into an .svg file, or in modern browsers
appear directly inline in the HTML5. However some attributes and other details differ slightly between these modes. This
DSL is biased toward the inline representation because that's its origin, but it supports indicating the rendering mode
and in the limitted scenarios tested it works.
Currently only a small set of SVG Elements are supported. Adding more is straight forward, I just met my own needs, and so additions can be done by others, or as my needs increase.
This is a multiplatform project currently targeting JVM and JavaScript. The JVM target is fully baked, the JavaScript is still a bit doughy. Looking for JavaScript folks to help me polish it.
Why did I write yet another SVG DSL when SVG is covered by the kotlinx.html?
Let's just say ... you try using it. I could not figure out how to use it based on the SVG specification. This package
is as close to a one to one mapping as I could make it. So what if you want to combine them? Not a problem, just use
unsafe/raw:
val svg = SVG.svg {
// ....
}
System.out.appendHTML().html {
body {
unsafe {
raw(svg.toString())
}
}
}