[Particles] Added attach to cam parameter.

h3d/parts/GpuParticles.hx

@@ -165,6 +165,8 @@ class GpuPartGroup {
 	public var colorGradient : h3d.mat.Texture	= null;
 
 	public var isRelative(default, set) : Bool	= false;
+	public var attachToCam(default, set) : Bool	= false;
+	public var distanceToCam(default, set) : Float	= 0;
 
 	inline function set_sortMode(v) { needRebuild = true; return sortMode = v; }
 	inline function set_size(v) { needRebuild = true; return size = v; }
@@ -189,6 +191,8 @@ class GpuPartGroup {
 	inline function set_rotSpeed(v) { needRebuild = true; return rotSpeed = v; }
 	inline function set_rotSpeedRand(v) { needRebuild = true; return rotSpeedRand = v; }
 	inline function set_isRelative(v) { needRebuild = true; return isRelative = v; }
+	inline function set_attachToCam(v) { needRebuild = true; return attachToCam = v; }
+	inline function set_distanceToCam(v) { needRebuild = true; return distanceToCam = v; }
 
 	public function new(parent) {
 		this.parent = parent;
@@ -963,7 +967,17 @@ class GpuParticles extends h3d.scene.MultiMaterial {
 					g.pshader.transform.load(absPos);
 				else
 					g.pshader.transform.identity();
-				g.pshader.offset.set(0, 0, 0);
+				if ( g.attachToCam ) {
+					ignoreParentTransform = true;
+					var camPos = ctx.camera.pos;
+					var camDir = ctx.camera.target.sub(ctx.camera.pos).normalized().clone();
+					var offset = camDir;
+					offset.scale(g.distanceToCam);
+					var emitterPos = camPos.add(offset);
+					g.pshader.offset.set( getAbsPos().getPosition().x + emitterPos.x, getAbsPos().getPosition().y + emitterPos.y, getAbsPos().getPosition().z + emitterPos.z );
+				}
+				else
+					g.pshader.offset.set(0, 0, 0);
 			}
 		}