Speed up and make more accurate relief mapping

using linear + binary search.

client/shaders/nodes_shader/opengl_fragment.glsl

@@ -47,15 +47,29 @@ vec4 get_normal_map(vec2 uv)
 
 float find_intersection(vec2 dp, vec2 ds)
 {
-	const float depth_step = 1.0 / 24.0;
 	float depth = 1.0;
-	for (int i = 0 ; i < 24 ; i++) {
+	float best_depth = 0.0;
+	float size = 0.0625;
+	for (int i = 0; i < 15; i++) {
+		depth -= size;
 		float h = texture2D(normalTexture, dp + ds * depth).a;
-		if (h >= depth)
+		if (depth <= h) {
+			best_depth = depth;
 			break;
-		depth -= depth_step;
+		}
 	}
-	return depth;
+	depth = best_depth;
+	for (int i = 0; i < 4; i++) {
+		size *= 0.5;
+		float h = texture2D(normalTexture,dp + ds * depth).a;
+		if (depth <= h) {
+			best_depth = depth;
+			depth += size;
+		} else {
+			depth -= size;
+		}
+	}
+	return best_depth;
 }
 
 float find_intersectionRGB(vec2 dp, vec2 ds)