gg: add cubic Bézier curves + examples (#11286)

examples/gg/bezier.v

@@ -0,0 +1,35 @@
+module main
+
+import gg
+import gx
+
+const (
+	p1_and_p2      = [f32(200.0), 200.0, 400.0, 300.0]
+	ctrl_p1_and_p2 = [f32(200.0), 100.0, 400.0, 100.0]
+)
+
+struct App {
+mut:
+	gg &gg.Context
+}
+
+fn main() {
+	mut app := &App{
+		gg: 0
+	}
+	app.gg = gg.new_context(
+		bg_color: gx.rgb(174, 198, 255)
+		width: 600
+		height: 400
+		window_title: 'Cubic Bézier curve'
+		frame_fn: frame
+		user_data: app
+	)
+	app.gg.run()
+}
+
+fn frame(mut app App) {
+	app.gg.begin()
+	app.gg.draw_cubic_bezier(p1_and_p2, ctrl_p1_and_p2, gx.blue)
+	app.gg.end()
+}

examples/gg/bezier_anim.v

@@ -0,0 +1,60 @@
+module main
+
+import gg
+import gx
+
+const rate = f32(1) / 60 * 10
+
+struct App {
+mut:
+	gg   &gg.Context
+	anim &Anim
+}
+
+struct Anim {
+mut:
+	time    f32
+	reverse bool
+}
+
+fn (mut anim Anim) advance() {
+	if anim.reverse {
+		anim.time -= 1 * rate
+	} else {
+		anim.time += 1 * rate
+	}
+	// Use some arbitrary value that fits 60 fps
+	if anim.time > 80 * rate || anim.time < -80 * rate {
+		anim.reverse = !anim.reverse
+	}
+}
+
+fn main() {
+	mut app := &App{
+		gg: 0
+		anim: &Anim{}
+	}
+	app.gg = gg.new_context(
+		bg_color: gx.rgb(174, 198, 255)
+		width: 600
+		height: 400
+		window_title: 'Animated cubic Bézier curve'
+		frame_fn: frame
+		user_data: app
+	)
+	app.gg.run()
+}
+
+fn frame(mut app App) {
+	time := app.anim.time
+
+	ctrl_p1_x := f32(200.0) + (40 * time)
+	ctrl_p2_x := f32(400.0) + (-40 * time)
+
+	p1_and_p2 := [f32(200.0), 200.0 + (10 * time), 400.0, 200.0 + (10 * time)]
+
+	app.gg.begin()
+	app.gg.draw_cubic_bezier(p1_and_p2, [ctrl_p1_x, 100.0, ctrl_p2_x, 100.0], gx.blue)
+	app.gg.end()
+	app.anim.advance()
+}