add some comments

bubulles.h

@@ -14,6 +14,7 @@ typedef struct {
 	unsigned long	reserved;
 	} XYZ;
 
+/* colors and transparency */
 typedef struct {
 	float		r, g, b, a;
 	unsigned long	reserved;
@@ -22,9 +23,9 @@ typedef struct {
 typedef struct {
 	XYZ		p;			/* position */
 	double  	d;			/* diameter */
-	int		gray;
+	int		gray;			/* used as an index */
 	RGBA		col;
-	long		ttl;
+	long		ttl;			/* bubulles can be aged */
 	double		kvalue;			/* wtf ? */
 	} Bubulle;