examples: add support for transparency / opacity / alpha in particle example (#6488)

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

@@ -27,7 +27,7 @@ fn remap(v, min, max, new_min, new_max f64) f64 {
 	return (((v - min) * (new_max - new_min)) / (max - min)) + new_min
 }
 
-// * Particle
+// Particle
 pub struct Particle {
 mut:
 	location       vec2.Vec2
@@ -49,7 +49,7 @@ pub fn (mut p Particle) update(dt f64) {
 		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))
+		p.color.a = byte(int(remap(p.life_time, 0.0, p.life_time_init, 0, 255))) - 10
 	} else {
 		p.life_time = 0
 	}

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

@@ -82,9 +82,7 @@ pub fn (mut s System) free() {
 			print(ptr_str(p) + ' ouch')
 			continue
 		}
-		unsafe {
-			free(p)
-		}
+		unsafe {free(p)}
 	}
 	s.pool.clear()
 	for p in s.bin {

examples/sokol/particles/particles.v

@@ -31,6 +31,7 @@ mut:
 	frame       i64
 	last        i64
 	ps          particle.System
+	alpha_pip   C.sgl_pipeline
 }
 
 fn (mut a App) init() {
@@ -66,16 +67,24 @@ fn (mut a App) run() {
 }
 
 fn (a App) draw() {
+	sgl.load_pipeline(a.alpha_pip)
 	a.ps.draw()
 }
 
 fn init(user_data voidptr) {
+	mut app := &App(user_data)
 	desc := sapp.create_desc()
 	gfx.setup(&desc)
 	sgl_desc := C.sgl_desc_t{
 		max_vertices: 50 * 65536
 	}
 	sgl.setup(&sgl_desc)
+	mut pipdesc := C.sg_pipeline_desc{}
+	unsafe {C.memset(&pipdesc, 0, sizeof(pipdesc))}
+	pipdesc.blend.enabled = true
+	pipdesc.blend.src_factor_rgb = C.SG_BLENDFACTOR_SRC_ALPHA
+	pipdesc.blend.dst_factor_rgb = C.SG_BLENDFACTOR_ONE_MINUS_SRC_ALPHA
+	app.alpha_pip = sgl.make_pipeline(&pipdesc)
 }
 
 fn cleanup(user_data voidptr) {
@@ -93,6 +102,7 @@ fn frame(user_data voidptr) {
 	app.ps.update(dt)
 	draw(app)
 	gfx.begin_default_pass(&app.pass_action, app.width, app.height)
+	sgl.default_pipeline()
 	sgl.draw()
 	gfx.end_pass()
 	gfx.commit()