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

examples/pendulum-simulation/sequential.v

@@ -0,0 +1,30 @@
+module main
+
+import benchmark
+import sim
+import sim.args as simargs
+import sim.img
+
+fn main() {
+	args := simargs.parse_args(sequential: true) ? as simargs.SequentialArgs
+
+	mut bmark := benchmark.start()
+	defer {
+		bmark.measure(@FN)
+	}
+
+	mut writer := img.ppm_writer_for_fname(args.filename, img.image_settings_from_grid(args.grid)) ?
+	defer {
+		writer.close()
+	}
+
+	handle_request := fn [mut writer] (request &sim.SimRequest) ? {
+		result := sim.compute_result(request)
+		pixel := img.compute_pixel(result)
+		return writer.handle_pixel(pixel)
+	}
+
+	sim.run(args.params, grid: args.grid, on_request: sim.SimRequestHandler(handle_request))
+
+	writer.write() ?
+}