distance from point to line

1// Get the normal distance from a point P to a line 
2// defined by two points L1 and L2:
3//
4// Formula:
5
6float normalDistanceToLine(vec2 P, vec2 L1, vec2 L2) {
7    float dividend = abs((L2.x - L1.x)*(L1.y - P.y) - (L1.x - P.x)*(L2.y - L1.y));
8    float divisor = sqrt(pow(L2.x - L1.x, 2) + pow(L2.y - L1.y, 2));
9  
10    if (divisor != 0.f) {
11        return dividend / divisor;
12    else		// Points L1 and L2 are the same, choose one
13      	return sqrt(pow(P.x - L1.x, 2) + pow(P.y - L1.y, 2));
14}
15  
16// With a distance function (maybe for a glsl shader)
17  
18float normalDistanceToLine(vec2 P, vec2 L1, vec2 L2) {
19  
20    float dist = distance(L1, L2);
21  
22    if (dist != 0.f) {
23        return abs((L2.x - L1.x)*(L1.y - P.y) - (L1.x - P.x)*(L2.y - L1.y)) / dist;
24    else		// Points L1 and L2 are the same, choose one
25      	return distance(P, L1);
26}
27