double STOPWATCH;

//pixel_source = pixel_for_bmap(Source_BM,Pixel_pos.x,Pixel_pos.y);
//pixel_to_bmap(NewSkin,Pixel_pos.x,Pixel_pos.y,pixel_dest);

//t_color = pixel_to_vec(NULL, t_alpha ,t_format2,pixel_source);
//pixel_dest=pixel_for_vec(t_color,t_alpha,t_format1);

//height = get_height(Pixel_pos.x,Pixel_pos.y,i,Terr);
height=random(200);

//retrieve first point of containing triangle (base corner)
	c1= ent_getvertex(Terrain,NULL,SW);
	Triangle[0].x=c1.v.x;
	Triangle[0].y=c1.v.z;
	Triangle[0].z=c1.v.y;
	
	//retrieve second point of containing triangle (diagonal to base)
	c1= ent_getvertex(Terrain,NULL,SW-32);
	Triangle[1].x=c1.v.x;
	Triangle[1].y=c1.v.z;
	Triangle[1].z=c1.v.y;
	
	//determine third point of containing triangle (varying point)
	vec_set (temp_vec, P);
	vec_sub (temp_vec,Triangle[0].x);
	vec_to_angle (temp_ang.pan,temp_vec);
	
	//retrieve third point of containing triangle (varying point)
	if(temp_ang.pan>45)
	{
		c1= ent_getvertex(Terrain,NULL,SW-33);
	}
	else
	{
		c1= ent_getvertex(Terrain,NULL,SW+1);
	}
	Triangle[2].x=c1.v.x;
	Triangle[2].y=c1.v.z;
	Triangle[2].z=c1.v.y;

//retrieve the three points of containing triangle

	//first, open the buffer
	ent_getvertex(Terrain,c1, 1);	ent_setvertex(Terrain,c1, 1);

	//retrieve the first point of containing triangle (diagonal to base)
	Triangle[0].x = c1.v[SW].x;
	Triangle[0].y = c1.v[SW].z;
	Triangle[0].z = c1.v[SW].y;
	
	//retrieve second point of containing triangle (diagonal to base)
	Triangle[1].x = c1.v[SW-32].x;
	Triangle[1].y = c1.v[SW-32].z;
	Triangle[1].z = c1.v[SW-32].y;
	
	//determine third point of containing triangle (varying point)
	vec_to_angle(temp_ang.pan, vec_sub( vec_set(temp_vec, P),Triangle[0].x));
	
	//retrieve third point of containing triangle (varying point)
	if(temp_ang.pan>45)
	{
		Triangle[2].x = c1.v[SW-33].x;
		Triangle[2].y = c1.v[SW-33].z;
		Triangle[2].z = c1.v[SW-33].y;
	}
	else
	{
		Triangle[2].x = c1.v[SW+1].x;
		Triangle[2].y = c1.v[SW+1].z;
		Triangle[2].z = c1.v[SW+1].y;
	}

this format
...  c1.v[SW].x  ...
may need changing to
...  (c1.v)[SW].x  ...