examples: improve the pendulum simulation, with several modes and diagrams (#13446)

examples/pendulum-simulation/modules/sim/img/worker.v

@@ -0,0 +1,40 @@
+module img
+
+import benchmark
+import sim
+
+pub fn image_worker(mut writer PPMWriter, result_chan chan &sim.SimResult, settings ImageSettings) {
+	width := settings.width
+	height := settings.height
+	total_pixels := width * height
+
+	// as new pixels come in, write them to the image file
+	mut current_index := u64(0)
+	mut pixel_buf := []ValidColor{len: total_pixels, init: ValidColor{
+		valid: false
+	}}
+
+	mut bmark := benchmark.new_benchmark()
+	for {
+		result := <-result_chan or { break }
+
+		// find the closest magnet
+		pixel_buf[result.id].Color = compute_pixel(result)
+		pixel_buf[result.id].valid = true
+
+		for current_index < total_pixels && pixel_buf[current_index].valid {
+			bmark.step()
+			writer.handle_pixel(pixel_buf[current_index].Color) or {
+				bmark.fail()
+				sim.log(@MOD + '.' + @FN + ': pixel handler failed. Error $err')
+				break
+			}
+			bmark.ok()
+			current_index++
+		}
+	}
+	bmark.stop()
+	println(bmark.total_message(@FN))
+
+	writer.write() or { panic('Could not write image') }
+}