Here is a working code for isometric view:

Code:
VECTOR mouse_click;

void mouseTo3D() {
	while (1) {
		if (mouse_left) {
			
			vec_set (mouse_click, mouse_dir3d); //get direction vector from mouse to world
			vec_normalize(mouse_click, 4000); //give it a large distance for tracing
			vec_add (mouse_click, mouse_pos3d); //calculate from camera mouse in 3d position
		
			c_trace (mouse_pos3d, mouse_click, IGNORE_MODELS); //trace from isometric 3d mouse position to clicked position (= mouse position + 4000 in depth)
			
			vec_set( mouse_click, target );
			ent_create ("warlock.mdl", mouse_click, NULL); //accurate warlock placement!
			
		}
	wait(1);
	}
}




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