float landscape::height_at( float x, float z) const{	if( x <= 0 ) return 0;	if( z <= 0 ) return 0;	if( x >= width ) return 0;	if( z >= height ) return 0;	int ax = int( x );	int az = int( z );	vector a( ax, data( ax, az), az);	vector b( ax + 1, data( ax + 1, az + 1), az + 1);	vector c;	// quad:	//	// +=====b	// |    /|	// |   / |	// |  /  |	// | /   |	// |/    |	// a=====+	//	// depending on which triangle our point is on,	// we put c at one of the +	float localx = ax - x;		// where they are within the square	float localz = az - z;	if ( localx < localz )	// which triangle they are on.							// To me, this inequality should be reversed, but it works this way.	{		c.x = ax + 1;		c.y = data( ax + 1, az );		c.z = az;	}	else	{		c.x = ax;		c.y = data( ax, az + 1 );		c.z = az + 1;	}	// now we have our copmlete triangle	vector n = vector::normal( a, b, c);	//	if ( n.y == 0) return 0; This seems impossible, it would mean a flat wall.	return ( n.dot(a) - ( n.z * z + n.x * x ) ) / n.y; // this follows from 													   // seperating y from the plane equation.}inline float landscape::data( int x, int z) const{	return land_data[ z * width + x ];}