examples: add fireworks example (#8358)

examples/fireworks/modules/objects/particle.v

@@ -0,0 +1,35 @@
+module objects
+
+import gg
+import gx
+
+pub struct Particle {
+pub mut:
+	color    gx.Color
+	pos      Vector
+	vel      Vector
+	accel    Vector
+	lifespan f32 = 255
+}
+
+pub fn (particle Particle) draw(mut ctx gg.Context) {
+	ctx.draw_circle(particle.pos.x, height - particle.pos.y, particle_radius, particle.color)
+}
+
+pub fn (mut particle Particle) tick(mut rocket Rocket, mut ctx gg.Context) {
+	particle.lifespan -= age_rate
+	particle.color.a = byte(particle.lifespan)
+
+	if particle.lifespan <= 0 {
+		rocket.dead = true
+		return
+	}
+
+	particle.accel += gravity
+	particle.vel += particle.accel
+	particle.vel = particle.vel.mult(drag)
+	particle.pos += particle.vel
+	particle.draw(mut ctx)
+
+	particle.accel = {}
+}