Re: Altium Designer DRC
There are two types of DRC checking in Alitum Designer - Online, and batch. What you are asking for is called "online" checking. It slows down the reponse of the PCB Editor, but it checks the entire board each time you make a change and marks the violations it finds.
To turn on online checking, go to Tools>Design Rule Check, click on "Rules to Check" and check the appropriate selection boxes in the "Online" column of the dialog. Now you will get a green marker where there are DRC vilolations.
Note that you don't really have to enable the online checks for the rules to be enforced by the software. Whatever you have enabled in Design>Rules will prevent you from violating the rule. To enable a rule, just go to the design rule dialog (Design>Rules), click on the top item in the list where it says "Design Rules", and you will see a table of all of the rules. Check the applicable boxes in the column that says "Enabled" to turn on the rule. All the "online" check setting described above does is give you a visual color mark where there are violations. Just having the rule enabled keeps you from violating the rule but doesn't give the mark.