diff --git a/Cargo.lock b/Cargo.lock
index 3c017bd..c703144 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -145,6 +145,8 @@ version = "0.1.0"
 dependencies = [
  "approx",
  "clap",
+ "serde",
+ "serde_derive",
  "stl_io",
 ]
 
@@ -175,6 +177,26 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "serde"
+version = "1.0.203"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7253ab4de971e72fb7be983802300c30b5a7f0c2e56fab8abfc6a214307c0094"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.203"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "500cbc0ebeb6f46627f50f3f5811ccf6bf00643be300b4c3eabc0ef55dc5b5ba"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "stl_io"
 version = "0.7.0"
diff --git a/Cargo.toml b/Cargo.toml
index ce042aa..e8d213e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,4 +6,6 @@ edition = "2021"
 [dependencies]
 approx = "0.5.1"
 clap = { version = "4.5.4", features = ["derive"] }
+serde = "1.0.203"
+serde_derive = "1.0.203"
 stl_io = "0.7.0"
diff --git a/src/layers.rs b/src/layers.rs
new file mode 100644
index 0000000..a15fbf0
--- /dev/null
+++ b/src/layers.rs
@@ -0,0 +1,94 @@
+use stl_io::{self, Vertex};
+
+use crate::mushroom::Mushroom;
+
+#[derive(Debug, PartialEq, Clone)]
+pub struct Layer {
+    /// Stalk height in millimeters. Zero for default.
+    pub center: Vertex,
+
+    /// Stalk diameter in millimeters. Zero for default.
+    pub radius: f32,
+}
+
+impl Layer {
+    pub fn new() -> Self {
+        return Self {
+            center: Vertex::new([1.0, 0.0, 0.0]),
+            radius: 0.0,
+        };
+    }
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub struct Layers {
+    pub base: Vertex,
+    pub layers: Vec<Layer>,
+    pub top: Vertex,
+}
+
+impl Layers {
+    pub fn max_radius(&self) -> f32 {
+        let mut max_radius: f32 = 0.0;
+        for layer in &self.layers {
+            max_radius = max_radius.max(layer.radius);
+        }
+        return max_radius;
+    }
+}
+
+fn stalk_layers(mushroom: &Mushroom, base: &Vertex, _resolution: f32) -> Vec<Layer> {
+    let stalk_top = Vertex::new([base[0], base[1], base[2] + mushroom.stalk_h]);
+
+    return [
+        Layer {
+            center: base.clone(),
+            radius: mushroom.stalk_r,
+        },
+        Layer {
+            center: stalk_top,
+            radius: mushroom.stalk_r,
+        },
+    ]
+    .to_vec();
+}
+
+fn cap_layers(mushroom: &Mushroom, base: &Vertex, _resolution: f32) -> Vec<Layer> {
+    let top = Vertex::new([base[0], base[1], base[2] + mushroom.cap_h]);
+
+    return [
+        Layer {
+            center: base.clone(),
+            radius: mushroom.cap_r,
+        },
+        Layer {
+            center: top,
+            radius: mushroom.cap_r,
+        },
+    ]
+    .to_vec();
+}
+
+pub fn mushroom(mushroom: &Mushroom, resolution: f32) -> Layers {
+    let _vertical_steps = (mushroom.height() / resolution) as u32;
+
+    let base = Vertex::new([0.0, 0.0, 0.0]);
+
+    // Get layers for the stalk.
+    let mut stalk_layers = stalk_layers(mushroom, &base, resolution);
+
+    // Get layers for the cap.
+    let cap_base = stalk_layers.last().unwrap().center;
+    let mut cap_layers = cap_layers(mushroom, &cap_base, resolution);
+
+    // The very top of the mushroom is directly above the top layer of the cap (or even with it)
+    // at the exact height of the total mushroom.
+    let cap_top = &cap_layers.last().unwrap().center;
+    let top = Vertex::new([cap_top[0], cap_top[1], base[2] + mushroom.height()]);
+
+    // Assemble the final Layers object.
+    let mut layers: Vec<Layer> = Vec::new();
+    layers.append(&mut stalk_layers);
+    layers.append(&mut cap_layers);
+    return Layers { base, top, layers };
+}
diff --git a/src/main.rs b/src/main.rs
index 0cf65a4..8da02bd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,4 @@
+pub mod layers;
 pub mod mushroom;
 pub mod render;
 
@@ -6,8 +7,30 @@ use clap::Parser;
 use std::fs::OpenOptions;
 
 extern crate approx;
+pub use serde_derive::{Deserialize, Serialize};
 
-// TODO: Investigate https://github.com/virtualritz/polyhedron-ops.
+fn main() {
+    let args = Args::parse();
+
+    // Define the mushroom.
+    let mushroom = mushroom_from_args(&args);
+
+    // Render the mushroom.
+    // let mesh = render::cylinder(mushroom.stalk_h, mushroom.stalk_d, 128);
+    let layers = layers::mushroom(&mushroom, 0.1);
+    let mesh = render::render(&layers, 0.1);
+
+    // Save output to file.
+    let mut file = OpenOptions::new()
+        .write(true)
+        .create(true)
+        .truncate(true)
+        .open(&args.output)
+        .unwrap();
+    stl_io::write_stl(&mut file, mesh.iter()).unwrap();
+
+    println!("Generated from: {:?}", mushroom);
+}
 
 #[derive(Parser, Debug, Clone)]
 #[command(version, about, long_about = None)]
@@ -35,6 +58,10 @@ struct Args {
     /// Stalk diameter in millimeters. Zero for default.
     #[arg(long, default_value_t = 0)]
     cap_d: u32,
+
+    /// Shape of the cap.
+    #[arg(long, default_value_t, value_enum)]
+    cap_style: mushroom::CapStyle,
 }
 
 fn mushroom_from_args(args: &Args) -> Mushroom {
@@ -48,52 +75,33 @@ fn mushroom_from_args(args: &Args) -> Mushroom {
             args.height as f32 * 0.66
         }
     };
-    let stalk_d: f32 = if args.stalk_d != 0 {
+    let stalk_r: f32 = if args.stalk_d != 0 {
         args.stalk_d as f32
     } else {
         args.height as f32 / 10.
-    };
+    } / 2.0; // computer the diamter, and convert to radius.
     let cap_h: f32 = if args.cap_h != 0 {
         args.cap_h as f32
     } else {
         args.height as f32 - stalk_h
     };
-    let cap_d: f32 = if args.cap_d != 0 {
+    let cap_r: f32 = if args.cap_d != 0 {
         args.cap_d as f32
     } else {
         args.height as f32
-    };
+    } / 2.0; // computer the diamter, and convert to radius.
+
+    let cap_style = args.cap_style.clone();
 
     Mushroom {
         stalk_h,
-        stalk_d,
+        stalk_r,
         cap_h,
-        cap_d,
+        cap_r,
+        cap_style,
     }
 }
 
-fn main() {
-    let args = Args::parse();
-
-    // Define the mushroom.
-    let mushroom = mushroom_from_args(&args);
-
-    // Render the mushroom.
-    // let mesh = render::cylinder(mushroom.stalk_h, mushroom.stalk_d, 128);
-    let mesh = render::mushroom(&mushroom);
-
-    // Save output to file.
-    let mut file = OpenOptions::new()
-        .write(true)
-        .create(true)
-        .truncate(true)
-        .open(&args.output)
-        .unwrap();
-    stl_io::write_stl(&mut file, mesh.iter()).unwrap();
-
-    println!("Generated from: {:?}", mushroom);
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -102,9 +110,10 @@ mod tests {
     fn validate_mushroom_from_args<I, T>(
         string_args: I,
         stalk_h: f32,
-        stalk_d: f32,
+        stalk_r: f32,
         cap_h: f32,
-        cap_d: f32,
+        cap_r: f32,
+        cap_style: mushroom::CapStyle,
     ) where
         I: IntoIterator<Item = T>,
         T: Into<OsString> + Clone,
@@ -115,31 +124,47 @@ mod tests {
             result,
             Mushroom {
                 stalk_h,
-                stalk_d,
+                stalk_r,
                 cap_h,
-                cap_d
+                cap_r,
+                cap_style,
             }
         );
     }
 
     #[test]
     fn defaults() {
-        validate_mushroom_from_args(["prog"], 66., 10., 34., 100.);
+        validate_mushroom_from_args(
+            ["prog"],
+            66.0,
+            5.0,
+            34.0,
+            50.0,
+            mushroom::CapStyle::Cylinder,
+        );
     }
 
     #[test]
     fn height_only() {
-        validate_mushroom_from_args(["prog", "--height", "200"], 132., 20., 68., 200.);
+        validate_mushroom_from_args(
+            ["prog", "--height", "200"],
+            132.0,
+            10.0,
+            68.0,
+            100.0,
+            mushroom::CapStyle::Cylinder,
+        );
     }
 
     #[test]
     fn height_stalk_h() {
         validate_mushroom_from_args(
             ["prog", "--height", "200", "--stalk-h", "20"],
-            20.,
-            20.,
-            180.,
-            200.,
+            20.0,
+            10.0,
+            180.0,
+            100.0,
+            mushroom::CapStyle::Cylinder,
         );
     }
 
@@ -147,10 +172,11 @@ mod tests {
     fn height_cap_h() {
         validate_mushroom_from_args(
             ["prog", "--height", "200", "--cap-h", "20"],
-            180.,
-            20.,
-            20.,
-            200.,
+            180.0,
+            10.0,
+            20.0,
+            100.0,
+            mushroom::CapStyle::Cylinder,
         );
     }
 
@@ -169,11 +195,14 @@ mod tests {
                 "40",
                 "--cap-d",
                 "50",
+                "--cap-style",
+                "dome",
             ],
-            20.,
-            30.,
-            40.,
-            50.,
+            20.0,
+            15.0,
+            40.0,
+            25.0,
+            mushroom::CapStyle::Dome,
         );
     }
 }
diff --git a/src/mushroom.rs b/src/mushroom.rs
index e683a0b..068db84 100644
--- a/src/mushroom.rs
+++ b/src/mushroom.rs
@@ -1,14 +1,38 @@
+use serde_derive::Serialize;
+
+#[derive(clap::ValueEnum, Clone, Default, Debug, Serialize, PartialEq)]
+pub enum CapStyle {
+    #[default]
+    Cylinder,
+    Dome,
+    Pointed,
+}
+
 #[derive(Debug, PartialEq)]
 pub struct Mushroom {
     /// Stalk height in millimeters. Zero for default.
     pub stalk_h: f32,
 
     /// Stalk diameter in millimeters. Zero for default.
-    pub stalk_d: f32,
+    pub stalk_r: f32,
 
     /// Cap height in millimeters. Zero for default.
     pub cap_h: f32,
 
     /// Stalk diameter in millimeters. Zero for default.
-    pub cap_d: f32,
+    pub cap_r: f32,
+
+    pub cap_style: CapStyle,
+}
+
+impl Mushroom {
+    /// Total height of the mushroom.
+    pub fn height(&self) -> f32 {
+        return self.stalk_h + self.cap_h;
+    }
+
+    /// Maximum radius of the mushroom.
+    pub fn radius(&self) -> f32 {
+        return self.stalk_r.max(self.cap_r) / 2.0;
+    }
 }
diff --git a/src/render.rs b/src/render.rs
index 4b4aed1..b4f4045 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -1,6 +1,6 @@
 use stl_io::{self, Normal, Triangle, Vertex};
 
-use crate::mushroom::Mushroom;
+use crate::layers::{Layer, Layers};
 
 fn new_triangle(p1: &Vertex, p2: &Vertex, p3: &Vertex) -> stl_io::Triangle {
     // Set Vector U to (Triangle.p2 minus Triangle.p1)
@@ -40,10 +40,10 @@ fn vertex_on_circle(center: &Vertex, radius: f32, angle: f32) -> Vertex {
     return Vertex::new([x, y, z]);
 }
 
-fn vertexes_on_circle(center: &Vertex, radius: f32, steps: u32) -> Vec<Vertex> {
+fn vertexes_on_circle(layer: &Layer, steps: u32) -> Vec<Vertex> {
     return radian_steps(steps)
         .iter()
-        .map(|angle| vertex_on_circle(center, radius, *angle))
+        .map(|angle| vertex_on_circle(&layer.center, layer.radius, *angle))
         .collect();
 }
 
@@ -80,46 +80,35 @@ fn tube_top(center: &Vertex, edge: &Vec<Vertex>) -> Vec<Triangle> {
     return tube_base(&center, &edge);
 }
 
-pub fn mushroom(mushroom: &Mushroom) -> Vec<Triangle> {
-    // Max size of any flat surface in mm.
-    let resolution: f32 = 1.0;
+pub fn render(layers: &Layers, resolution: f32) -> Vec<Triangle> {
+    // Top and Bottom must be a single point, and must be at least one middle layer.
+    assert!(!layers.layers.is_empty());
 
-    // We always use the same number of diameter steps to ensure the number of circular vertices doesn't change,
-    // which might create small breaks in our model.
-    let diameter_steps = std::cmp::max(
-        (mushroom.cap_d * std::f32::consts::TAU * resolution) as u32,
-        64,
-    );
+    // How many vertexes per circle. IE: the resolution of the circle.
+    let circle_steps =
+        ((layers.max_radius() * std::f32::consts::TAU) / resolution).max(64.0) as u32;
 
-    let stalk_base_center = Vertex::new([0.0, 0.0, 0.0]);
-    let stalk_base_edge = vertexes_on_circle(&stalk_base_center, mushroom.stalk_d, diameter_steps);
-    let stalk_top_center = Vertex::new([
-        stalk_base_center[0],
-        stalk_base_center[1],
-        stalk_base_center[2] + mushroom.stalk_h,
-    ]);
-    let stalk_top_edge = vertexes_on_circle(&stalk_top_center, mushroom.stalk_d, diameter_steps);
-    let cap_base_edge = vertexes_on_circle(&stalk_top_center, mushroom.cap_d, diameter_steps);
-    let cap_top_center = Vertex::new([
-        stalk_top_center[0],
-        stalk_top_center[1],
-        stalk_top_center[2] + mushroom.cap_h,
-    ]);
-    let cap_top_edge = vertexes_on_circle(&cap_top_center, mushroom.cap_d, diameter_steps);
+    let mut layer_vertexes: Vec<Vec<Vertex>> = Vec::new();
 
-    let mut result = Vec::new();
+    for layer in &layers.layers {
+        layer_vertexes.push(vertexes_on_circle(&layer, circle_steps));
+    }
 
-    result.append(&mut tube_base(&stalk_base_center, &stalk_base_edge));
-    result.append(&mut tube_sides(&stalk_base_edge, &stalk_top_edge));
-    result.append(&mut tube_sides(&stalk_top_edge, &cap_base_edge));
-    result.append(&mut tube_sides(&cap_base_edge, &cap_top_edge));
-    result.append(&mut tube_top(&cap_top_center, &cap_top_edge));
+    let mut result: Vec<Triangle> = Vec::new();
+
+    result.append(&mut tube_base(&layers.base, &layer_vertexes[0]));
+    for i in 0..layer_vertexes.len() - 1 {
+        result.append(&mut tube_sides(&layer_vertexes[i], &layer_vertexes[i + 1]));
+    }
+    result.append(&mut tube_top(&layers.top, &layer_vertexes.last().unwrap()));
 
     return result;
 }
 
 #[cfg(test)]
 mod tests {
+    use approx::relative_eq;
+
     use super::*;
 
     #[test]
@@ -196,7 +185,13 @@ mod tests {
 
     #[test]
     fn vertexes_on_circle_basic() {
-        let val = vertexes_on_circle(&Vertex::new([0.0, 0.0, 0.0]), 1.0, 4);
+        let val = vertexes_on_circle(
+            &Layer {
+                center: Vertex::new([0.0, 0.0, 0.0]),
+                radius: 1.0,
+            },
+            4,
+        );
 
         let expected = [
             Vertex::new([1.0, 0.0, 0.0]),
@@ -211,7 +206,13 @@ mod tests {
 
     #[test]
     fn vertexes_on_circle_complex() {
-        let val = vertexes_on_circle(&Vertex::new([4.0, 5.0, 6.0]), 3.0, 4);
+        let val = vertexes_on_circle(
+            &Layer {
+                center: Vertex::new([4.0, 5.0, 6.0]),
+                radius: 3.0,
+            },
+            4,
+        );
 
         let expected = [
             Vertex::new([7.0, 5.0, 6.0]),
@@ -229,7 +230,13 @@ mod tests {
         // fn tube_base(center: &Vertex, edge: &Vec<Vertex>) -> Vec<Triangle> {
 
         let center = Vertex::new([0.0, 0.0, 0.0]);
-        let edge = vertexes_on_circle(&center, 1.0, 4);
+        let edge = vertexes_on_circle(
+            &Layer {
+                center: center.clone(),
+                radius: 1.0,
+            },
+            4,
+        );
 
         let triangles = tube_base(&center, &edge);
 
@@ -244,7 +251,13 @@ mod tests {
     #[test]
     fn tube_top_test() {
         let center = Vertex::new([0.0, 0.0, 0.0]);
-        let edge = vertexes_on_circle(&center, 1.0, 4);
+        let edge = vertexes_on_circle(
+            &Layer {
+                center: center.clone(),
+                radius: 1.0,
+            },
+            4,
+        );
 
         let triangles = tube_top(&center, &edge);
 
@@ -255,4 +268,38 @@ mod tests {
             assert_eq!(t.normal, Vertex::new([0.0, 0.0, 1.0]));
         }
     }
+
+    #[test]
+    fn render_test() {
+        let layers = Layers {
+            base: Vertex::new([0.0, 0.0, 0.0]),
+            layers: [
+                Layer {
+                    center: Vertex::new([0.0, 0.0, 1.0]),
+                    radius: 1.0,
+                },
+                Layer {
+                    center: Vertex::new([0.0, 0.0, 2.0]),
+                    radius: 1.0,
+                },
+            ]
+            .to_vec(),
+            top: Vertex::new([0.0, 0.0, 3.0]),
+        };
+
+        let mesh = render(&layers, 10.0); // Large resolution ensures minimum steps of 64.
+
+        // 64 triangles for top, 128 for sides, 64 for bottom.
+        assert_eq!(mesh.len(), 64 + 128 + 64);
+
+        for i in 0..mesh.len() {
+            if i < 64 {
+                assert!(mesh[i].normal[2] < 0.0) // Bottom triangles point down.
+            } else if i < (64 + 128) {
+                assert!(mesh[i].normal[2] == 0.0) // side triangles point out.
+            } else {
+                assert!(mesh[i].normal[2] > 0.0) // top triangles point up.
+            }
+        }
+    }
 }