--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pkg/mesh/areas.go	Tue Nov 05 14:30:22 2019 +0100
@@ -0,0 +1,88 @@
+// This is Free Software under GNU Affero General Public License v >= 3.0
+// without warranty, see README.md and license for details.
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+// License-Filename: LICENSES/AGPL-3.0.txt
+//
+// Copyright (C) 2018 by via donau
+//   – Österreichische Wasserstraßen-Gesellschaft mbH
+// Software engineering by Intevation GmbH
+//
+// Author(s):
+//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>
+
+package mesh
+
+import (
+	"runtime"
+	"sync"
+
+	"gemma.intevation.de/gemma/pkg/common"
+)
+
+func GenerateRandomVertices(
+	n int,
+	min, max Vertex,
+	eval func(float64, float64) (float64, bool),
+	callback func([]Vertex),
+) {
+	var wg sync.WaitGroup
+
+	jobs := make(chan int)
+	out := make(chan []Vertex)
+	done := make(chan struct{})
+
+	cpus := runtime.NumCPU()
+
+	free := make(chan []Vertex, cpus)
+
+	for i := 0; i < cpus; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			xRange := common.Random(min.X, max.X)
+			yRange := common.Random(min.Y, max.Y)
+
+			for size := range jobs {
+				var vertices []Vertex
+				select {
+				case vertices = <-free:
+				default:
+					vertices = make([]Vertex, 0, 1000)
+				}
+				for len(vertices) < size {
+					x, y := xRange(), yRange()
+					if z, ok := eval(x, y); ok {
+						vertices = append(vertices, Vertex{X: x, Y: y, Z: z})
+					}
+				}
+				out <- vertices
+			}
+		}()
+	}
+
+	go func() {
+		defer close(done)
+		for vertices := range out {
+			callback(vertices)
+			select {
+			case free <- vertices[:0]:
+			default:
+			}
+		}
+	}()
+
+	for remain := n; remain > 0; {
+		if remain > 1000 {
+			jobs <- 1000
+			remain -= 1000
+		} else {
+			jobs <- remain
+			remain = 0
+		}
+	}
+	close(jobs)
+	wg.Wait()
+	close(out)
+	<-done
+}