Drawing per-vertex colored meshes and variable thickness lines

[abe]

The code above was a preparation for this program, which converts an open animated shapeContour into a mesh (a triangle strip) with variable width and unique colors per vertex.

imports

import org.openrndr.application
import org.openrndr.color.ColorRGBa
import org.openrndr.draw.DrawPrimitive
import org.openrndr.draw.shadeStyle
import org.openrndr.draw.vertexBuffer
import org.openrndr.draw.vertexFormat
import org.openrndr.extensions.Screenshots
import org.openrndr.extra.noise.Random
import org.openrndr.math.Polar
import org.openrndr.shape.ShapeContour

fun main() = application {
    configure {
        width = 800
        height = 800
    }
    program {
        val geometry = vertexBuffer(vertexFormat {
            position(3)
            color(4)
        }, 100)

        extend(Screenshots())
        extend {
            drawer.clear(ColorRGBa.WHITE)
            drawer.shadeStyle = shadeStyle {
                fragmentTransform = "x_fill = va_color;"
            }
            val line = ShapeContour.fromPoints(List(geometry.vertexCount / 2) {
                val theta = it * 10.0 + seconds * 20
                val radius = 200.0 + 80 * Random.perlin(theta * 0.01, 1.0)
                Polar(theta, radius).cartesian + drawer.bounds.center
            }, false)
            
            val points = geometry.vertexCount / 2
            geometry.put {
                for (i in 0 until points) {
                    val pc = i / (points - 1.0)
                    val color = ColorRGBa.GRAY.mix(ColorRGBa.PINK, pc).toVector4()
                    val pos = line.position(pc)
                    val normal = line.normal(pc).normalized *
                            (40 + 20 * Random.perlin(pos * 0.01))
                    write((pos + normal).vector3(z = 0.0))
                    write(color)
                    write((pos - normal).vector3(z = 0.0))
                    write(color)
                }
            }
            drawer.vertexBuffer(geometry, DrawPrimitive.TRIANGLE_STRIP)
        }
    }
}