examples: move the particle module in modules/particle

The goal is enabling running `v build-examples` from outside vroot.
The modules/ folders are already skipped when building examples.

examples/sokol/particles/modules/particle/particle.v

@@ -0,0 +1,81 @@
+// 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 particle
+
+import vec2
+import sokol.sgl
+
+const (
+	default_life_time = 1000
+	default_v_color   = Color{93, 136, 193, 255}
+)
+
+// * Module public
+pub fn new(location vec2.Vec2) &Particle {
+	p := &Particle{
+		location: location
+		velocity: vec2.Vec2{0, 0}
+		acceleration: vec2.Vec2{0, 0}
+		color: default_v_color
+		life_time: default_life_time
+		life_time_init: default_life_time
+	}
+	return p
+}
+
+fn remap(v, min, max, new_min, new_max f64) f64 {
+	return (((v - min) * (new_max - new_min)) / (max - min)) + new_min
+}
+
+// * Particle
+pub struct Particle {
+mut:
+	location       vec2.Vec2
+	velocity       vec2.Vec2
+	acceleration   vec2.Vec2
+	color          Color
+	life_time      f64
+	life_time_init f64
+}
+
+pub fn (mut p Particle) update(dt f64) {
+	mut acc := p.acceleration
+	acc.multiply_f64(dt)
+	p.velocity = p.velocity.add(acc)
+	p.location = p.location.add(p.velocity)
+	lt := p.life_time - (1000 * dt)
+	if lt > 0 {
+		p.life_time = lt
+		p.color.r = p.color.r - 1 // byte(remap(p.life_time,0.0,p.life_time_init,0,p.color.r))
+		p.color.g = p.color.g - 1 // byte(remap(p.life_time,0.0,p.life_time_init,0,p.color.g))
+		p.color.b = p.color.b - 1 // byte(remap(p.life_time,0.0,p.life_time_init,0,p.color.b))
+		// p.color.a = byte(remap(p.life_time,0.0,p.life_time_init,0,255))
+	} else {
+		p.life_time = 0
+	}
+}
+
+pub fn (p Particle) is_dead() bool {
+	return p.life_time <= 0.0
+}
+
+pub fn (p Particle) draw() {
+	l := p.location
+	sgl.c4b(p.color.r, p.color.g, p.color.b, p.color.a)
+	lx := f32(l.x)
+	ly := f32(l.y)
+	sgl.v2f(lx, ly)
+	sgl.v2f(lx + 2, ly)
+	sgl.v2f(lx + 2, ly + 2)
+	sgl.v2f(lx, ly + 2)
+}
+
+pub fn (mut p Particle) reset() {
+	p.location.zero()
+	p.acceleration.zero()
+	p.velocity.zero()
+	// p.color = Color{93, 136, 193, 255}
+	p.color = default_v_color
+	p.life_time = default_life_time
+	p.life_time_init = p.life_time
+}