diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73c10eb..c35d1fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,12 @@
 
 All notable changes to Swift Loop. Versions follow SemVer; the [v0.x.y] anchor links to the GitHub release.
 
+## [Unreleased]
+
+### Added
+- **Angle Z (pseudo-3D depth).** The Iterations section now has a second rotation: the old **Angle** is renamed **Angle XY** (the in-plane spiral/swirl), and **Angle Z** tilts each cell's offset into depth. The tool is flat 2D — Figma, Penpot, and SVG have no depth axis — so the tilt is computed in 3D and orthographically projected back to 2D. A flat spiral leans into a cone or helix; a ring squashes into an ellipse seen at an angle. Output stays plain 2D positions, so it exports and round-trips like everything else. Library entries can declare an optional `angleZ`.
+- **Depth shading.** A **Depth** dial (0–100%) sells the 3D illusion: cells leaning toward the viewer grow and stay bright, cells leaning away shrink and dim. It scales/fades on top of the Scale and Opacity sliders and does nothing without a nonzero Angle Z (no tilt, no depth to shade). Library entries can declare an optional `depthShade`.
+
 ## [v0.2.0] — 2026-05-22
 
 ### Added
diff --git a/docs/controls.md b/docs/controls.md
index d1f3d19..2e4cdd2 100644
--- a/docs/controls.md
+++ b/docs/controls.md
@@ -22,7 +22,11 @@ The first section. This is where you set the count.
 
 **Rows.** How many rows. 1 to 100. Leave at 1 for linear and radial patterns.
 
-**Angle.** Degrees of per-cell rotation, applied to each clone's grid offset around the source center. Leave at 0 for straight lines and rectangular grids. Bump it 5 to 30 degrees and a line curls into a spiral, a grid swirls. Crank it past 90 to wrap the pattern back around on itself. Think "how much do successive cells lean".
+**Angle XY.** Degrees of per-cell rotation in the screen plane, applied to each clone's grid offset around the source center. Leave at 0 for straight lines and rectangular grids. Bump it 5 to 30 degrees and a line curls into a spiral, a grid swirls. Crank it past 90 to wrap the pattern back around on itself. Think "how much do successive cells lean".
+
+**Angle Z.** Degrees of per-cell tilt into depth, applied after Angle XY. The tool is flat 2D, so there's no real depth axis — instead each clone's offset is tilted toward/away from you and projected back onto the canvas, which foreshortens it. Leave at 0 to stay flat. Dial it up and a flat spiral leans into a cone or helix, a ring squashes into an ellipse seen at an angle. Because it's a projection, the result is still plain 2D positions, so it exports and round-trips like everything else.
+
+**Depth.** How hard to sell the 3D illusion, 0 to 100%. With Angle Z doing the tilt, this scales and fades each clone by how far it leans toward or away from you: the near side grows and stays bright, the far side shrinks and dims. It does nothing on its own — you need a nonzero Angle Z for there to be any depth to shade. At 0% you get pure projection (shapes keep their size); crank it up and the cone or helix reads as genuinely three-dimensional. Note this rides on top of your Scale and Opacity sliders, so a cell's final size is the slider value times the depth factor.
 
 If you've applied a library pattern, you'll also see a little pill showing its name. Click it to jump back to the library and pick something else.
 
diff --git a/docs/llm-pattern-guide.md b/docs/llm-pattern-guide.md
index 333809d..27a6b21 100644
--- a/docs/llm-pattern-guide.md
+++ b/docs/llm-pattern-guide.md
@@ -47,7 +47,9 @@ You, the LLM reading this, are helping a designer write a new library pattern. Y
 | `author` | recommended | `@handle` form. |
 | `cols` | yes | Integer 1 to 100. The default column count when the pattern loads. |
 | `rows` | yes | Integer 1 to 100. The default row count. Use `1` for linear or radial patterns. |
-| `angle` | optional | Number, -360 to 360. Per-cell rotation in degrees applied to the grid offset around the source center, *after* the formulas compute `x` and `y`. Cell `i` is rotated by `angle * i`. Lets a pattern declare a spiral or swirl without folding the rotation into every formula. Default `0`. See "Using `angle`" below. |
+| `angle` | optional | Number, -360 to 360. Per-cell rotation in degrees applied to the grid offset *in the screen plane*, *after* the formulas compute `x` and `y`. Cell `i` is rotated by `angle * i`. Lets a pattern declare a spiral or swirl without folding the rotation into every formula. Default `0`. See "Using `angle`" below. |
+| `angleZ` | optional | Number, -360 to 360. Per-cell tilt into depth in degrees, applied *after* `angle` and orthographically projected back to 2D (the tool is flat — there is no real depth axis). Cell `i` is tilted by `angleZ * i`, foreshortening its offset; a flat spiral leans into a cone/helix, a ring squashes into an ellipse. Output is still plain 2D positions. Default `0`. |
+| `depthShade` | optional | Number, 0 to 100. Depth-cue strength: scales and fades each cell by how far its `angleZ` tilt leans it toward (bigger/brighter) or away from (smaller/dimmer) the viewer. No effect without a nonzero `angleZ`. Rides on top of the scale/opacity values. Default `0` (pure projection). |
 | `showFirst` | optional | Defaults to `true`. Set to `false` only for radial or spiral patterns where the `i=0` clone naturally lands away from the origin, and you want the source shape to stay visually centered. See "showFirst" below. |
 | `formulas` | yes | Object. Any subset of `x`, `y`, `rotation`, `scaleX`, `scaleY`, `opacity`. Omit properties that should stay at their default. |
 
diff --git a/library/_schema.json b/library/_schema.json
index 25f5adb..458b4c6 100644
--- a/library/_schema.json
+++ b/library/_schema.json
@@ -16,7 +16,19 @@
       "type": "number",
       "minimum": -360,
       "maximum": 360,
-      "description": "Per-cell rotation in degrees applied to the grid offset around the source center. Cell i is rotated by `angle * i`. Use with cols ≥ 2 to trace spirals or swirl a 2D grid."
+      "description": "Per-cell rotation in degrees applied to the grid offset in the screen plane. Cell i is rotated by `angle * i`. Use with cols ≥ 2 to trace spirals or swirl a 2D grid."
+    },
+    "angleZ": {
+      "type": "number",
+      "minimum": -360,
+      "maximum": 360,
+      "description": "Per-cell tilt into depth in degrees, applied after `angle` and orthographically projected to 2D. Cell i is tilted by `angleZ * i`, turning a flat spiral into a cone/helix. 0 = flat."
+    },
+    "depthShade": {
+      "type": "number",
+      "minimum": 0,
+      "maximum": 100,
+      "description": "Depth-cue strength (0..100) driven by the `angleZ` tilt: cells leaning toward the viewer grow, cells leaning away shrink and fade. No effect without a nonzero `angleZ`. 0 = off."
     },
     "showFirst": {
       "type": "boolean",
diff --git a/src/plugin/engine/angle.ts b/src/plugin/engine/angle.ts
index fa60ab9..b7195ee 100644
--- a/src/plugin/engine/angle.ts
+++ b/src/plugin/engine/angle.ts
@@ -1,21 +1,74 @@
 // src/plugin/engine/angle.ts
-// Rotates a grid offset around the source center by `angle * i` degrees,
-// where i is the cell's flat index. Lets a straight line of cells curl into
-// a spiral, or a rectangular grid swirl, without touching the formula layer.
+// Rotates a grid offset around the source center by `angle * i` degrees, then
+// optionally tilts it into depth by `angleZ * i` degrees and projects back to
+// 2D. Lets a straight line of cells curl into a spiral (XY), or a flat spiral
+// foreshorten into a cone/helix (Z), without touching the formula layer.
+//
+// The math is 3D internally but the output is plain 2D, so it round-trips to
+// SVG, Figma, and Penpot — none of which have a real depth axis.
+//
+//   p  = (x, y, 0)
+//   Rz: rotate in the screen plane by angleXY * i  (the classic spiral/swirl)
+//   Rx: tilt about the screen's horizontal axis by angleZ * i  (lean into depth)
+//   project orthographically: keep (x, y), drop the depth component
+//
+// Rotating about X with z = 0 leaves x untouched and foreshortens y by
+// cos(angleZ * i): a flat disc seen edge-on becomes an ellipse, and a per-cell
+// tilt turns a spiral into a corkscrew. angleZ = 0 reproduces the pure-XY
+// output exactly.
+//
+// `depth` is the discarded component, normalized by the offset's magnitude to
+// [-1, 1]: +1 = leaning fully toward the viewer, -1 = fully away, 0 = in the
+// screen plane. Consumers use it as a depth cue (near = bigger/brighter).
 
 const DEG_TO_RAD = Math.PI / 180
 
+export interface RotatedOffset {
+  x: number
+  y: number
+  depth: number // normalized depth toward the viewer in [-1, 1]
+}
+
+export function rotateOffset(
+  values: { x: number; y: number },
+  i: number,
+  angleDegrees: number,
+  angleZDegrees = 0,
+): RotatedOffset {
+  let x = values.x
+  let y = values.y
+
+  if (angleDegrees !== 0) {
+    const theta = angleDegrees * i * DEG_TO_RAD
+    const cos = Math.cos(theta)
+    const sin = Math.sin(theta)
+    const rx = x * cos - y * sin
+    const ry = x * sin + y * cos
+    x = rx
+    y = ry
+  }
+
+  let depth = 0
+  if (angleZDegrees !== 0) {
+    const phi = angleZDegrees * i * DEG_TO_RAD
+    const z = y * Math.sin(phi)
+    y = y * Math.cos(phi)
+    // hypot of the pre-rotation offset — magnitude is rotation-invariant, so it
+    // equals the magnitude of the in-plane (x, y) we just rotated.
+    const mag = Math.hypot(values.x, values.y)
+    depth = mag === 0 ? 0 : z / mag
+  }
+
+  return { x, y, depth }
+}
+
 export function applyAngleToOffset(
   values: { x: number; y: number },
   i: number,
   angleDegrees: number,
+  angleZDegrees = 0,
 ): { x: number; y: number } {
-  if (angleDegrees === 0) return values
-  const theta = angleDegrees * i * DEG_TO_RAD
-  const cos = Math.cos(theta)
-  const sin = Math.sin(theta)
-  return {
-    x: values.x * cos - values.y * sin,
-    y: values.x * sin + values.y * cos,
-  }
+  if (angleDegrees === 0 && angleZDegrees === 0) return { x: values.x, y: values.y }
+  const r = rotateOffset(values, i, angleDegrees, angleZDegrees)
+  return { x: r.x, y: r.y }
 }
diff --git a/src/plugin/engine/cells.ts b/src/plugin/engine/cells.ts
index e53e976..e020c85 100644
--- a/src/plugin/engine/cells.ts
+++ b/src/plugin/engine/cells.ts
@@ -5,7 +5,7 @@
 // Figma node, build an SVG element, etc.).
 
 import type { CompiledFormulas, LoopConfig, Scope } from '../../shared/types'
-import { applyAngleToOffset } from './angle'
+import { rotateOffset } from './angle'
 import type { CompiledFactors } from './compile'
 import { applyEasing } from './easing'
 import { buildScope } from './scope'
@@ -18,10 +18,13 @@ export interface CellValues {
   // Grid offset after angle rotation.
   x: number
   y: number
+  // Normalized depth toward the viewer in [-1, 1] after the Angle Z tilt; 0
+  // when angleZ is 0. Surfaced for consumers that want a custom depth cue.
+  depth: number
   rotation: number
-  scaleX: number
+  scaleX: number // depth shading already folded in (additive px delta to source size)
   scaleY: number
-  opacity: number // raw evaluated value (0..100); consumers clamp/normalize
+  opacity: number // raw evaluated value (0..100), depth shading folded in; consumers clamp/normalize
   // Per-property lerp factors in [0, 1] (formula-resolved or eased fallback).
   fillFactor: number
   strokeFactor: number
@@ -51,11 +54,30 @@ export function evaluateCell(i: number, input: EvaluateCellInput): CellValues {
     c,
     r,
   )
-  const rotated = applyAngleToOffset(
+  const rotated = rotateOffset(
     { x: compiled.x.evaluate(scope, 'x'), y: compiled.y.evaluate(scope, 'y') },
     scope.i,
     config.angle,
+    config.angleZ ?? 0,
   )
+  let scaleX = compiled.scaleX.evaluate(scope, 'scaleX')
+  let scaleY = compiled.scaleY.evaluate(scope, 'scaleY')
+  let opacity = compiled.opacity.evaluate(scope, 'opacity')
+
+  // Depth shading: use the projected depth as a near/far cue. Cells leaning
+  // toward the viewer grow; cells leaning away shrink and fade. Strength is a
+  // 0..100 dial. No-op when there's no tilt (depth = 0) or the dial is off, so
+  // it never touches flat patterns.
+  const depthShade = config.depthShade ?? 0
+  if (depthShade !== 0 && rotated.depth !== 0) {
+    const k = depthShade / 100
+    const sizeFactor = 1 + k * rotated.depth // [1-k, 1+k]
+    scaleX = (sourceWidth + scaleX) * sizeFactor - sourceWidth
+    scaleY = (sourceHeight + scaleY) * sizeFactor - sourceHeight
+    // Brightening past full opacity is meaningless, so only the far side fades.
+    if (rotated.depth < 0) opacity *= 1 + k * rotated.depth
+  }
+
   const baseEased = applyEasing(config.easing, computeInterpFactor(config, scope.tx, scope.ty))
   return {
     i,
@@ -64,10 +86,11 @@ export function evaluateCell(i: number, input: EvaluateCellInput): CellValues {
     scope,
     x: rotated.x,
     y: rotated.y,
+    depth: rotated.depth,
     rotation: compiled.rotation.evaluate(scope, 'rotation'),
-    scaleX: compiled.scaleX.evaluate(scope, 'scaleX'),
-    scaleY: compiled.scaleY.evaluate(scope, 'scaleY'),
-    opacity: compiled.opacity.evaluate(scope, 'opacity'),
+    scaleX,
+    scaleY,
+    opacity,
     fillFactor: factors.fill ? factors.fill.evaluate(scope, 'fillFactor') : baseEased,
     strokeFactor: factors.stroke ? factors.stroke.evaluate(scope, 'strokeFactor') : baseEased,
     strokeWeightFactor: factors.strokeWeight
diff --git a/src/plugin/loop/diff.ts b/src/plugin/loop/diff.ts
index feb26d9..076c8f6 100644
--- a/src/plugin/loop/diff.ts
+++ b/src/plugin/loop/diff.ts
@@ -42,16 +42,29 @@ export function diffConfig(
     return { mode: 'full', dirty: ALL_PROPS }
   }
 
-  // angle re-rotates every cell's grid offset, so x and y must be re-applied.
-  const angleChanged = (prev.angle ?? 0) !== (next.angle ?? 0)
+  // angle / angleZ re-rotate every cell's grid offset, so x and y must be
+  // re-applied when either changes.
+  const angleChanged =
+    (prev.angle ?? 0) !== (next.angle ?? 0) || (prev.angleZ ?? 0) !== (next.angleZ ?? 0)
+  const xChanged = !eqNumericProperty(prev.x, next.x)
+  const yChanged = !eqNumericProperty(prev.y, next.y)
+
+  // Depth shading derives scale and opacity from each cell's projected depth,
+  // which depends on x/y and the angles. So when shading is active, any change
+  // to those must re-apply scaleX/scaleY/opacity; toggling the dial itself
+  // always does.
+  const depthShadeChanged = (prev.depthShade ?? 0) !== (next.depthShade ?? 0)
+  const depthActive = (prev.depthShade ?? 0) !== 0 || (next.depthShade ?? 0) !== 0
+  const depthDirtiesSize =
+    depthShadeChanged || (depthActive && (angleChanged || xChanged || yChanged))
 
   const dirty: DirtyProperty[] = []
-  if (!eqNumericProperty(prev.x, next.x) || angleChanged) dirty.push('x')
-  if (!eqNumericProperty(prev.y, next.y) || angleChanged) dirty.push('y')
+  if (xChanged || angleChanged) dirty.push('x')
+  if (yChanged || angleChanged) dirty.push('y')
   if (!eqNumericProperty(prev.rotation, next.rotation)) dirty.push('rotation')
-  if (!eqNumericProperty(prev.scaleX, next.scaleX)) dirty.push('scaleX')
-  if (!eqNumericProperty(prev.scaleY, next.scaleY)) dirty.push('scaleY')
-  if (!eqNumericProperty(prev.opacity, next.opacity)) dirty.push('opacity')
+  if (!eqNumericProperty(prev.scaleX, next.scaleX) || depthDirtiesSize) dirty.push('scaleX')
+  if (!eqNumericProperty(prev.scaleY, next.scaleY) || depthDirtiesSize) dirty.push('scaleY')
+  if (!eqNumericProperty(prev.opacity, next.opacity) || depthDirtiesSize) dirty.push('opacity')
   if (JSON.stringify(prev.fill) !== JSON.stringify(next.fill)) dirty.push('fill')
   if (JSON.stringify(prev.stroke) !== JSON.stringify(next.stroke)) dirty.push('stroke')
   if (!eqNumericProperty(prev.strokeWeight, next.strokeWeight)) dirty.push('strokeWeight')
diff --git a/src/shared/defaults.ts b/src/shared/defaults.ts
index e76e34e..51ca0d5 100644
--- a/src/shared/defaults.ts
+++ b/src/shared/defaults.ts
@@ -23,6 +23,8 @@ export const DEFAULT_CONFIG: LoopConfig = {
   cols: 10,
   rows: 10,
   angle: 0,
+  angleZ: 0,
+  depthShade: 0,
   x: num(60),
   y: num(60),
   rotation: num(0),
@@ -48,6 +50,8 @@ export const RESET_CONFIG: LoopConfig = {
   cols: 1,
   rows: 1,
   angle: 0,
+  angleZ: 0,
+  depthShade: 0,
   x: num(0),
   y: num(0),
   rotation: num(0),
diff --git a/src/shared/types.ts b/src/shared/types.ts
index d4bba87..10d9e20 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -41,10 +41,23 @@ export interface LoopConfig {
   // Iteration
   cols: number
   rows: number
-  // Degrees of per-cell rotation around the source center, applied to the
-  // grid offset (values.x, values.y) post-formula. Cell i is rotated by
-  // angle * i degrees, so a 1-row line + nonzero angle traces a spiral.
+  // Degrees of per-cell rotation in the screen plane (around the view's Z
+  // axis), applied to the grid offset (values.x, values.y) post-formula. Cell
+  // i is rotated by angle * i degrees, so a 1-row line + nonzero angle traces a
+  // spiral. Surfaced in the UI as "Angle XY".
   angle: number
+  // Degrees of per-cell tilt into depth (rotation about the screen's horizontal
+  // X axis), applied after `angle` and orthographically projected back to 2D.
+  // Cell i is tilted by angleZ * i degrees; the depth component is dropped, so
+  // a flat spiral foreshortens into a cone/helix. 0 = flat (output identical to
+  // angle alone). Surfaced in the UI as "Angle Z". Optional for back-compat
+  // with saved configs and library entries that predate it.
+  angleZ?: number
+  // Strength (0..100) of the depth cue driven by the Angle Z tilt: cells
+  // leaning toward the viewer grow, cells leaning away shrink and fade. 0 = off
+  // (pure orthographic projection). No effect without a nonzero angleZ. Surfaced
+  // in the UI as "Depth". Optional for back-compat.
+  depthShade?: number
 
   // Base transforms (per-step)
   x: NumericProperty
diff --git a/src/ui/library/types.ts b/src/ui/library/types.ts
index d3dbe57..15b8db2 100644
--- a/src/ui/library/types.ts
+++ b/src/ui/library/types.ts
@@ -9,11 +9,19 @@ export interface LibraryEntry {
   author?: string
   cols: number
   rows: number
-  /** Optional per-cell rotation around the source center (degrees).
+  /** Optional per-cell rotation in the screen plane (degrees).
    *  Cell i's grid offset is rotated by `angle * i` post-formula. Lets a
    *  pattern declare a spiral or swirl without folding the rotation into
    *  every x/y formula. Omit (or 0) for unrotated patterns. */
   angle?: number
+  /** Optional per-cell tilt into depth (degrees), applied after `angle` and
+   *  orthographically projected back to 2D. Cell i is tilted by `angleZ * i`,
+   *  turning a flat spiral into a cone/helix. Omit (or 0) for flat patterns. */
+  angleZ?: number
+  /** Optional depth-cue strength (0..100) driven by the `angleZ` tilt: cells
+   *  leaning toward the viewer grow, cells leaning away shrink and fade. No
+   *  effect without a nonzero `angleZ`. Omit (or 0) for no depth shading. */
+  depthShade?: number
   showFirst?: boolean
   formulas: Partial<Record<FormulaProperty, string>>
 }
diff --git a/src/ui/sections/IterationsSection.tsx b/src/ui/sections/IterationsSection.tsx
index 9c95627..1fa7da1 100644
--- a/src/ui/sections/IterationsSection.tsx
+++ b/src/ui/sections/IterationsSection.tsx
@@ -75,7 +75,7 @@ export function IterationsSection({
         onChange={(v, commit) => update({ ...config, rows: Math.max(1, Math.round(v)) }, commit)}
       />
       <SliderRow
-        label="Angle"
+        label="Angle XY"
         value={config.angle}
         min={-180}
         max={180}
@@ -83,6 +83,24 @@ export function IterationsSection({
         unit="°"
         onChange={(v, commit) => update({ ...config, angle: v }, commit)}
       />
+      <SliderRow
+        label="Angle Z"
+        value={config.angleZ ?? 0}
+        min={-180}
+        max={180}
+        step={0.1}
+        unit="°"
+        onChange={(v, commit) => update({ ...config, angleZ: v }, commit)}
+      />
+      <SliderRow
+        label="Depth"
+        value={config.depthShade ?? 0}
+        min={0}
+        max={100}
+        step={1}
+        unit="%"
+        onChange={(v, commit) => update({ ...config, depthShade: v }, commit)}
+      />
     </Section>
   )
 }
diff --git a/src/ui/sections/LibraryOverlay.tsx b/src/ui/sections/LibraryOverlay.tsx
index 05c46a0..159526b 100644
--- a/src/ui/sections/LibraryOverlay.tsx
+++ b/src/ui/sections/LibraryOverlay.tsx
@@ -35,6 +35,8 @@ function applyEntry(config: LoopConfig, entry: LibraryEntry): LoopConfig {
     cols: entry.cols,
     rows: entry.rows,
     angle: entry.angle ?? 0,
+    angleZ: entry.angleZ ?? 0,
+    depthShade: entry.depthShade ?? 0,
     fxMode: true,
     showFirst: entry.showFirst ?? true,
   }
diff --git a/tests/angle.test.ts b/tests/angle.test.ts
index cc2cbca..ef830f2 100644
--- a/tests/angle.test.ts
+++ b/tests/angle.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { applyAngleToOffset } from '../src/plugin/engine/angle'
+import { applyAngleToOffset, rotateOffset } from '../src/plugin/engine/angle'
 
 describe('applyAngleToOffset', () => {
   it('returns the input unchanged when angle is zero', () => {
@@ -50,4 +50,64 @@ describe('applyAngleToOffset', () => {
     expect(r.x).toBeCloseTo(3 * s - 4 * s, 6)
     expect(r.y).toBeCloseTo(3 * s + 4 * s, 6)
   })
+
+  describe('angleZ (depth tilt, orthographic projection)', () => {
+    it('is backward compatible: angleZ=0 matches the pure-XY result', () => {
+      for (let i = 1; i <= 6; i++) {
+        const flat = applyAngleToOffset({ x: 30, y: 40 }, i, 17)
+        const withZero = applyAngleToOffset({ x: 30, y: 40 }, i, 17, 0)
+        expect(withZero.x).toBeCloseTo(flat.x, 6)
+        expect(withZero.y).toBeCloseTo(flat.y, 6)
+      }
+    })
+
+    it('leaves x untouched and foreshortens y by cos(angleZ × i)', () => {
+      // angleZ only (no XY): x is unchanged, y scales by cos(angleZ × i).
+      const r = applyAngleToOffset({ x: 10, y: 20 }, 1, 0, 60)
+      expect(r.x).toBeCloseTo(10, 6)
+      expect(r.y).toBeCloseTo(20 * Math.cos((60 * Math.PI) / 180), 6) // 20 × 0.5
+    })
+
+    it('collapses y to 0 when the tilt reaches edge-on (angleZ × i = 90°)', () => {
+      const r = applyAngleToOffset({ x: 10, y: 20 }, 1, 0, 90)
+      expect(r.x).toBeCloseTo(10, 6)
+      expect(r.y).toBeCloseTo(0, 6)
+    })
+
+    it('applies the depth tilt after the in-plane rotation', () => {
+      // Rz(90°) sends (10,0) -> (0,10); then Rx tilt foreshortens that y by cos(60°).
+      const r = applyAngleToOffset({ x: 10, y: 0 }, 1, 90, 60)
+      expect(r.x).toBeCloseTo(0, 6)
+      expect(r.y).toBeCloseTo(10 * Math.cos((60 * Math.PI) / 180), 6) // 5
+    })
+
+    it('returns the origin unchanged regardless of either angle', () => {
+      const r = applyAngleToOffset({ x: 0, y: 0 }, 4, 30, 45)
+      expect(r.x).toBeCloseTo(0, 6)
+      expect(r.y).toBeCloseTo(0, 6)
+    })
+  })
+})
+
+describe('rotateOffset depth', () => {
+  it('reports zero depth when there is no Z tilt', () => {
+    expect(rotateOffset({ x: 30, y: 40 }, 2, 25).depth).toBe(0)
+  })
+
+  it('is ±1 when the offset tilts fully toward / away (angleZ × i = ±90°)', () => {
+    // offset along +y, no XY rotation: the tilt sends it fully into depth.
+    expect(rotateOffset({ x: 0, y: 40 }, 1, 0, 90).depth).toBeCloseTo(1, 6)
+    expect(rotateOffset({ x: 0, y: 40 }, 1, 0, -90).depth).toBeCloseTo(-1, 6)
+  })
+
+  it('normalizes depth to the offset magnitude (scale-independent)', () => {
+    const small = rotateOffset({ x: 0, y: 10 }, 1, 0, 30).depth
+    const big = rotateOffset({ x: 0, y: 1000 }, 1, 0, 30).depth
+    expect(small).toBeCloseTo(big, 6)
+    expect(small).toBeCloseTo(Math.sin((30 * Math.PI) / 180), 6)
+  })
+
+  it('reports zero depth at the origin (no magnitude to normalize against)', () => {
+    expect(rotateOffset({ x: 0, y: 0 }, 3, 40, 45).depth).toBe(0)
+  })
 })
diff --git a/tests/cells.test.ts b/tests/cells.test.ts
index 48fc02c..e2c5797 100644
--- a/tests/cells.test.ts
+++ b/tests/cells.test.ts
@@ -15,7 +15,7 @@ function reference(
   i: number,
   sw: number,
   sh: number,
-): Omit<CellValues, 'scope'> {
+): Omit<CellValues, 'scope' | 'depth'> {
   const compiled = compileConfig(config)
   const factors = compileFactors(config)
   const c = i % config.cols
@@ -88,6 +88,67 @@ describe('evaluateCell', () => {
     expect(run(DEFAULT_CONFIG, 4).opacity).toBeCloseTo(100, 6)
   })
 
+  it('depth shading grows toward-viewer cells and keeps their opacity', () => {
+    // angle 90° sends the +x offset onto +y; angleZ 90° tilts that fully toward
+    // the viewer (depth +1). depthShade 50% → sizeFactor 1.5 on a 40×30 source.
+    const config: LoopConfig = {
+      ...DEFAULT_CONFIG,
+      cols: 2,
+      rows: 1,
+      angle: 90,
+      angleZ: 90,
+      depthShade: 50,
+      x: { ...DEFAULT_CONFIG.x, value: 100 },
+      y: { ...DEFAULT_CONFIG.y, value: 0 },
+      scaleX: { ...DEFAULT_CONFIG.scaleX, value: 0 },
+      scaleY: { ...DEFAULT_CONFIG.scaleY, value: 0 },
+    }
+    const cell = run(config, 1, 40, 30)
+    expect(cell.depth).toBeCloseTo(1, 6)
+    expect(cell.scaleX).toBeCloseTo(20, 6) // 40 × 1.5 − 40
+    expect(cell.scaleY).toBeCloseTo(15, 6) // 30 × 1.5 − 30
+    expect(cell.opacity).toBeCloseTo(100, 6) // near side never over-brightens
+  })
+
+  it('depth shading shrinks and fades away-from-viewer cells', () => {
+    const config: LoopConfig = {
+      ...DEFAULT_CONFIG,
+      cols: 2,
+      rows: 1,
+      angle: 90,
+      angleZ: -90, // tilt away → depth −1
+      depthShade: 50,
+      x: { ...DEFAULT_CONFIG.x, value: 100 },
+      y: { ...DEFAULT_CONFIG.y, value: 0 },
+      scaleX: { ...DEFAULT_CONFIG.scaleX, value: 0 },
+      scaleY: { ...DEFAULT_CONFIG.scaleY, value: 0 },
+    }
+    const cell = run(config, 1, 40, 30)
+    expect(cell.depth).toBeCloseTo(-1, 6)
+    expect(cell.scaleX).toBeCloseTo(-20, 6) // 40 × 0.5 − 40
+    expect(cell.scaleY).toBeCloseTo(-15, 6) // 30 × 0.5 − 30
+    expect(cell.opacity).toBeCloseTo(50, 6) // 100 × 0.5
+  })
+
+  it('depth shading is a no-op when depthShade is 0 (pure projection)', () => {
+    const config: LoopConfig = {
+      ...DEFAULT_CONFIG,
+      cols: 2,
+      rows: 1,
+      angle: 90,
+      angleZ: 90,
+      depthShade: 0,
+      x: { ...DEFAULT_CONFIG.x, value: 100 },
+      y: { ...DEFAULT_CONFIG.y, value: 0 },
+      scaleX: { ...DEFAULT_CONFIG.scaleX, value: 7 },
+      scaleY: { ...DEFAULT_CONFIG.scaleY, value: 0 },
+    }
+    const cell = run(config, 1, 40, 30)
+    expect(cell.scaleX).toBeCloseTo(7, 6)
+    expect(cell.scaleY).toBeCloseTo(0, 6)
+    expect(cell.opacity).toBeCloseTo(100, 6)
+  })
+
   it('falls back to the eased base factor when a ramp has no formula', () => {
     const config: LoopConfig = { ...DEFAULT_CONFIG, cols: 5, rows: 1, easing: 'linear' }
     const cell = run(config, 3)