examples: add a gg timer example, drawing the result coming from a worker thread (#10065)

examples/gg/worker_thread.v

@@ -0,0 +1,91 @@
+// Copyright(C) 2019 Lars Pontoppidan. All rights reserved.
+// Use of this source code is governed by an MIT license file distributed with this software package.
+module main
+
+// Example of how to send a value through a channel from a worker thread to the main/rendering thread.
+// This can be useful to do long running computations while keeping your framerate high (60 fps in this example).
+import gg
+import gx
+import math
+import time
+
+const (
+	win_width   = 600
+	win_height  = 700
+	bg_color    = gx.white
+	count_color = gx.black
+)
+
+struct App {
+mut:
+	gg      &gg.Context
+	ch      chan i64
+	counter i64
+}
+
+fn main() {
+	mut app := &App{
+		gg: 0
+	}
+	app.gg = gg.new_context(
+		width: win_width
+		height: win_height
+		use_ortho: true // This is needed for 2D drawing
+		create_window: true
+		window_title: 'Counter'
+		user_data: app
+		bg_color: bg_color
+		frame_fn: frame
+		init_fn: init
+		font_path: gg.system_font_path()
+	)
+	app.gg.run()
+}
+
+fn init(mut app App) {
+	// Spawn a new worker thread.
+	go worker(mut app)
+}
+
+// worker simulates a workload. This should be run in a separate thread.
+fn worker(mut app App) {
+	stopwatch := time.new_stopwatch({})
+	mut elapsed := stopwatch.elapsed()
+	// Do heavy operations here - like invoking a path finding algorithm, load an image or similar.
+	for {
+		now := stopwatch.elapsed()
+		// When done - send the result through a channel to the main/rendering thread.
+		app.ch <- (now - elapsed)
+		elapsed = now
+		time.sleep(1 * time.second)
+	}
+}
+
+fn frame(mut app App) {
+	app.gg.begin()
+	size := gg.window_size()
+	mut scale_factor := math.round(f32(size.width) / win_width)
+	if scale_factor <= 0 {
+		scale_factor = 1
+	}
+	text_cfg := gx.TextCfg{
+		size: 64 * int(scale_factor)
+	}
+
+	// Try a pop from the channel
+	mut count := i64(0)
+	if app.ch.try_pop(mut count) == .success {
+		// A value was assigned - increase the counter
+		app.counter += i64(f64(count) / time.second)
+	}
+
+	label := '$app.counter'
+	label_width := (f64(label.len * text_cfg.size) / 4.0)
+	label_height := (f64(1 * text_cfg.size) / 2.0)
+	mut x := f32(size.width) * 0.5 - label_width
+	mut y := f32(size.height) * 0.5 - label_height
+
+	app.gg.draw_text(int(x), int(y), label, text_cfg)
+
+	app.gg.end()
+}