point size attenuation fix

examples/webgl_nearestneighbour.html

@@ -45,7 +45,7 @@
 
 				vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
 
-				gl_PointSize = 4.0 * ( 300.0 / length( mvPosition.xyz ) );
+				gl_PointSize = 4.0 * ( 300.0 / -mvPosition.z );
 
 				gl_Position = projectionMatrix * mvPosition;