diff --git a/src/tools/minimap.rs b/src/tools/minimap.rs
index a903c647..bcfed217 100644
--- a/src/tools/minimap.rs
+++ b/src/tools/minimap.rs
@@ -187,7 +187,7 @@ pub fn generate(
     'atom: for atom in atoms {
         // At this time, space is invisible. Earlier steps need to process it.
         for pass in render_passes.iter() {
-            if !pass.final_filter(&atom, objtree) {
+            if !pass.late_filter(&atom, objtree) {
                 continue 'atom;
             }
         }
diff --git a/src/tools/render_passes/mod.rs b/src/tools/render_passes/mod.rs
index cb011ab2..46143145 100644
--- a/src/tools/render_passes/mod.rs
+++ b/src/tools/render_passes/mod.rs
@@ -1,9 +1,51 @@
 use dm::objtree::*;
 use minimap::Atom;
 
+/// A map rendering pass.
+///
+/// These methods are applied to any given atom in roughly the order they
+/// appear here.
 #[allow(unused_variables)]
 pub trait RenderPass {
-    fn final_filter(&self, atom: &Atom, objtree: &ObjectTree) -> bool { true }
+    /// Filter atoms at the beginning of the process.
+    ///
+    /// Return `false` to discard the atom.
+    fn early_filter(&self,
+        atom: &Atom,
+        objtree: &ObjectTree,
+    ) -> bool { true }
+
+    /// Expand atoms, such as spawners into the atoms they spawn.
+    ///
+    /// Return `true` to consume the original atom.
+    fn expand(&self,
+        atom: &Atom,
+        objtree: &ObjectTree,
+        output: &mut Vec<Atom>,
+    ) -> bool { false }
+
+    /// Adjust the variables of an atom.
+    fn adjust_vars(&self,
+        atom: &mut Atom,
+        objtree: &ObjectTree,
+    ) {}
+
+    /// Apply overlays and underlays to an atom, in the form of pseudo-atoms.
+    fn overlays(&self,
+        atom: &mut Atom,
+        objtree: &ObjectTree,
+        underlays: &mut Vec<Atom>,
+        overlays: &mut Vec<Atom>,
+    ) {}
+
+    /// Filter atoms at the end of the process.
+    ///
+    /// Will act on adjusted atoms and pseudo-atoms from `adjust_vars` and
+    /// `overlays`. Return `true` to keep and `false` to discard.
+    fn late_filter(&self,
+        atom: &Atom,
+        objtree: &ObjectTree,
+    ) -> bool { true }
 }
 
 pub struct RenderPassInfo {
@@ -55,7 +97,7 @@ pub fn configure(include: &str, exclude: &str) -> Vec<Box<RenderPass>> {
 #[derive(Default)]
 pub struct HideSpace;
 impl RenderPass for HideSpace {
-    fn final_filter(&self, atom: &Atom, _: &ObjectTree) -> bool {
+    fn late_filter(&self, atom: &Atom, _: &ObjectTree) -> bool {
         !atom.istype("/turf/open/space/")
     }
 }