Weird artifacts

Fragment Shader
uniform sampler2D Grass;
uniform sampler2D Stone;
uniform sampler2D Rock;
uniform sampler2D Alpha;

varying vec4 diffuse,ambientGlobal, ambient;
varying vec3 normal,lightDir,halfVector;
varying float dist;
	
vec4 cursorColor = vec4(1,0,0,1);
uniform float cursorSize;
uniform vec2 cursorPosition;

void main(void)
{
	
	//Texture Splatting

	vec2 texUV = gl_TexCoord[0].xy;
 
	vec4 alpha   = texture2D( Alpha, texUV.xy );

  	vec4 tex0    = texture2D( Grass, texUV.xy * 64.0 ); // Tile
  	vec4 tex1    = texture2D( Rock,  texUV.xy * 64.0 ); // Tile
   	vec4 tex2    = texture2D( Stone, texUV.xy * 64.0 ); // Tile

   	tex0 *= alpha.r; // Red channel
  	tex1 = mix( tex0, tex1, alpha.g ); // Green channel
  	vec4 outColor = mix( tex1, tex2, alpha.b ); // Blue channel
   
	
	//Drawing a Editing-Brush for the Terrain
	float distRing = distance(texUV.xy, cursorPosition);
	if(distRing < cursorSize)
	{
	float strength = max(0.0, mix(-1.5, 0.5, distRing / cursorSize));
	outColor += cursorColor * strength;
	}
		
	//gl_FragColor = outColor;


	//Per Pixel Lighting
	float startAlpha = gl_Color.w;

	vec3 n,halfV,viewV,ldir;
	float NdotL,NdotHV;
	vec4 color = ambientGlobal;
	float att;
		
	n = normalize(normal);
	
	NdotL = max(dot(n,normalize(lightDir)),0.0);


	if (NdotL > 0.0) 
	{
		att = 1.0 / (gl_LightSource[0].constantAttenuation + 

gl_LightSource[0].linearAttenuation * dist + gl_LightSource[0].quadraticAttenuation * dist * dist);
		color += att * (diffuse * NdotL + ambient);
		
			
		halfV = normalize(halfVector);
		NdotHV = max(dot(n,halfV),0.0);
		color += att * gl_FrontMaterial.specular * gl_LightSource[0].specular 		* 

pow(NdotHV,gl_FrontMaterial.shininess);
	}


	color.w = startAlpha;

	gl_FragColor = color*outColor;

}


Vertex Shader
varying vec4 diffuse,ambientGlobal,ambient;
varying vec3 normal,lightDir,halfVector;
varying float dist;

void main()
{
	gl_TexCoord[0] = gl_MultiTexCoord0; 
	

	//Per Pixel Lighting
	vec4 ecPos;
	vec3 aux;
		
	normal = normalize(gl_NormalMatrix * gl_Normal);
	
	ecPos = gl_ModelViewMatrix * gl_Vertex;
	aux = vec3(gl_LightSource[0].position-ecPos);
	lightDir = normalize(aux);
	dist = length(aux);
	
	halfVector = normalize(gl_LightSource[0].halfVector.xyz);
		
	
	diffuse = gl_FrontMaterial.diffuse * gl_LightSource[0].diffuse;

	ambient = gl_FrontMaterial.ambient * gl_LightSource[0].ambient;

	ambientGlobal = gl_LightModel.ambient * gl_FrontMaterial.ambient;
		

	gl_Position = ftransform();

}