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

examples/pendulum-simulation/modules/sim/anim/app.v

@@ -0,0 +1,64 @@
+module anim
+
+import gg
+import gx
+import sim
+import sim.args as simargs
+
+const bg_color = gx.white
+
+struct Pixel {
+	x     f32
+	y     f32
+	color gx.Color
+}
+
+struct App {
+pub:
+	args         simargs.ParallelArgs
+	request_chan chan &sim.SimRequest
+	result_chan  chan &sim.SimResult
+pub mut:
+	gg     &gg.Context = 0
+	iidx   int
+	pixels []u32
+}
+
+pub fn new_app(args simargs.ParallelArgs) &App {
+	total_pixels := args.grid.height * args.grid.width
+
+	mut app := &App{
+		args: args
+		pixels: []u32{len: total_pixels}
+		request_chan: chan &sim.SimRequest{cap: args.grid.width}
+	}
+	app.gg = gg.new_context(
+		width: args.grid.width
+		height: args.grid.height
+		create_window: true
+		window_title: 'V Pendulum Simulation'
+		user_data: app
+		bg_color: anim.bg_color
+		frame_fn: frame
+		init_fn: init
+	)
+	return app
+}
+
+fn init(mut app App) {
+	app.iidx = app.gg.new_streaming_image(app.args.grid.width, app.args.grid.height, 4,
+		pixel_format: .rgba8)
+	go pixels_worker(mut app)
+}
+
+fn frame(mut app App) {
+	app.gg.begin()
+	app.draw()
+	app.gg.end()
+}
+
+fn (mut app App) draw() {
+	mut istream_image := app.gg.get_cached_image_by_idx(app.iidx)
+	istream_image.update_pixel_data(&app.pixels[0])
+	app.gg.draw_image(0, 0, app.args.grid.width, app.args.grid.height, istream_image)
+}