diff --git a/src/composables/useShapeGenerator.ts b/src/composables/useShapeGenerator.ts
index 77e2ea5..412abf5 100644
--- a/src/composables/useShapeGenerator.ts
+++ b/src/composables/useShapeGenerator.ts
@@ -1,12 +1,21 @@
 // Builds a Minecraft elevation-view (front-facing) block list for a wall
-// panel with an arch- or oval-shaped opening cut out of it, smoothed with
-// slabs (half-block resolution) and stairs (beveled corners) instead of a
-// fully jagged hole outline.
+// panel with an arch- or oval-shaped opening cut out of it.
+//
+// Each block is sub-sampled at 4 quarter-points (splitting the block into a
+// 2x2 grid) against the true ellipse boundary, so the resulting shape is
+// derived directly from geometry rather than from an ad-hoc comparison
+// between neighboring columns:
+//   4/4 quarters solid -> full block
+//   3/4 solid           -> stair (the empty corner picks one of the 4
+//                          orientations - including upside-down ones)
+//   2/4 solid, split top/bottom -> slab (top or bottom)
+//   2/4 solid, split left/right or diagonally -> no clean single-block
+//                          shape; defaults to a full block
+//   0-1/4 solid          -> air (too little material to represent)
 //
 // Coordinate system: columns run left->right (x), rows run bottom->up (y).
 // The final shape always fills the whole `width x height` rectangle except
-// for the opening; the opening's boundary cells are what carry the
-// smoothing detail.
+// for the opening.
 
 export type CellType = 'full' | 'slab' | 'stair'
 export type Half = 'top' | 'bottom'
@@ -42,176 +51,76 @@ export interface GenerateOptions {
   useStairs: boolean
 }
 
-const EPS = 1e-9
-
-/**
- * Turn a continuous outward distance into a near-origin -> far-from-origin
- * list of solid cells, optionally using half-block quantization for one
- * extra level of smoothness. `dir` controls which half of a fractional cell
- * is solid:
- *   'up'   -> solid half is the one closer to the origin (bottom of the cell)
- *   'down' -> solid half is the one closer to the origin (top of the cell)
- */
-function buildProfileCells(distance: number, dir: 'up' | 'down', useSlabs: boolean): Cell[] {
-  const resolved = useSlabs ? Math.round(distance * 2) / 2 : Math.round(distance)
-  const fullBlocks = Math.floor(resolved + EPS)
-  const remainder = resolved - fullBlocks
-
-  const cells: Cell[] = []
-  for (let k = 0; k < fullBlocks; k++) {
-    cells.push({ type: 'full' })
-  }
-  if (useSlabs && remainder >= 0.5 - EPS) {
-    cells.push({ type: 'slab', half: dir === 'up' ? 'bottom' : 'top' })
-  }
-  return cells
+/** True when (x, y) falls inside the elliptical opening. */
+function insideOpening(x: number, y: number, a: number, b: number): boolean {
+  return (x / a) ** 2 + (y / b) ** 2 <= 1
 }
 
-function countSolid(cells: Cell[]): number {
-  let n = 0
-  for (const c of cells) if (c.type === 'full' || c.type === 'stair') n++
-  return n
+/** Continuous y-coordinate of a row's center: arch shapes sit on the ground (y=0 at the bottom edge), oval shapes are centered vertically. */
+function rowCenterY(r: number, mode: ShapeMode, height: number): number {
+  return mode === 'oval' ? r - (height - 1) / 2 : r + 0.5
 }
 
-/**
- * Convert the outermost full block of a column into a stair whenever the
- * neighbor farther from the center is exactly one whole block shorter.
- * Mutates `columns` in place.
- */
-function applyStairBevel(columns: Cell[][], centerSide: (i: number) => -1 | 0 | 1, dir: 'up' | 'down') {
-  const n = columns.length
-  for (let i = 0; i < n; i++) {
-    const cells = columns[i]
-    if (cells.length === 0) continue
-    const top = cells[cells.length - 1]
-    if (top.type !== 'full') continue // slabs already smooth this transition
+function classifyCell(tl: boolean, tr: boolean, bl: boolean, br: boolean, useSlabs: boolean, useStairs: boolean): Cell | null {
+  const count = (tl ? 1 : 0) + (tr ? 1 : 0) + (bl ? 1 : 0) + (br ? 1 : 0)
 
-    const side = centerSide(i)
-    if (side === 0) continue
+  if (count === 4) return { type: 'full' }
+  if (count <= 1) return null // not enough material to represent
 
-    const outwardIdx = side < 0 ? i - 1 : i + 1
-    const outwardFull = outwardIdx >= 0 && outwardIdx < n ? countSolid(columns[outwardIdx]) : 0
-    const ownFull = countSolid(cells)
-
-    if (ownFull - outwardFull === 1) {
-      top.type = 'stair'
-      top.half = dir === 'up' ? 'bottom' : 'top'
-      top.openSide = side < 0 ? 'left' : 'right'
-    }
-  }
-}
-
-interface HoleShape {
-  totalRows: number
-  columns: Column[]
-}
-
-/** Computes the solid "hole" shape (the arch mound / oval blob) that will later be subtracted from the wall. */
-function generateHoleShape(width: number, height: number, mode: ShapeMode, useSlabs: boolean, useStairs: boolean): HoleShape {
-  const a = width / 2
-  const bTop = mode === 'oval' ? height / 2 : height
-  const bBottom = mode === 'oval' ? height / 2 : 0
-  const centerOffset = (width - 1) / 2
-
-  const upCells: Cell[][] = []
-  const downCells: Cell[][] = []
-
-  for (let i = 0; i < width; i++) {
-    const dx = i - centerOffset
-    const t = Math.max(0, 1 - (dx / a) ** 2)
-    const yUp = bTop * Math.sqrt(t)
-    const yDown = bBottom * Math.sqrt(t)
-    upCells.push(buildProfileCells(yUp, 'up', useSlabs))
-    downCells.push(buildProfileCells(yDown, 'down', useSlabs))
+  if (count === 3) {
+    if (!useStairs) return { type: 'full' }
+    if (!tl) return { type: 'stair', half: 'bottom', openSide: 'left' }
+    if (!tr) return { type: 'stair', half: 'bottom', openSide: 'right' }
+    if (!bl) return { type: 'stair', half: 'top', openSide: 'left' }
+    return { type: 'stair', half: 'top', openSide: 'right' } // !br
   }
 
-  const centerSide = (i: number): -1 | 0 | 1 => {
-    const dx = i - centerOffset
-    if (Math.abs(dx) < EPS) return 0
-    return dx < 0 ? -1 : 1
-  }
-
-  if (useStairs) {
-    applyStairBevel(upCells, centerSide, 'up')
-    if (mode === 'oval') applyStairBevel(downCells, centerSide, 'down')
-  }
-
-  let rowsAbove = 0
-  let rowsBelow = 0
-  for (let i = 0; i < width; i++) {
-    rowsAbove = Math.max(rowsAbove, upCells[i].length)
-    rowsBelow = Math.max(rowsBelow, downCells[i].length)
-  }
-
-  const totalRows = rowsBelow + rowsAbove
-  const columns: Column[] = []
-  for (let i = 0; i < width; i++) {
-    const down = downCells[i].slice().reverse() // far-from-center -> near-center
-    const up = upCells[i] // near-center -> far-from-center
-    const col: Column = new Array(totalRows).fill(null)
-
-    for (let k = 0; k < down.length; k++) {
-      col[rowsBelow - down.length + k] = down[k]
-    }
-    for (let k = 0; k < up.length; k++) {
-      col[rowsBelow + k] = up[k]
-    }
-    columns.push(col)
-  }
-
-  return { totalRows, columns }
-}
-
-/**
- * Subtract a hole shape from a solid `width x hole.totalRows` wall.
- *
- * The arch mound only has one real curved surface (its top - it sits flush
- * on the ground, so its bottom is just the grid edge, not a smoothing
- * boundary). The oval blob floats free and has two curved surfaces (top and
- * bottom). `preserveBottomBoundary` selects between the two: when false,
- * everything from the grid bottom up to (and excluding) the top boundary
- * cell becomes air; when true, the bottom boundary cell is kept too and only
- * the interior between the two boundaries becomes air.
- */
-function invertToWall(hole: HoleShape, width: number, preserveBottomBoundary: boolean): Shape {
-  const rows = hole.totalRows
-  const columns: Column[] = hole.columns.map((col) => {
-    let lo = -1
-    let hi = -1
-    for (let r = 0; r < col.length; r++) {
-      if (col[r]) {
-        if (lo === -1) lo = r
-        hi = r
-      }
-    }
-
-    const newCol: Column = new Array(rows)
-    if (lo === -1) {
-      for (let r = 0; r < rows; r++) newCol[r] = { type: 'full' }
-      return newCol
-    }
-
-    const airFrom = preserveBottomBoundary ? lo + 1 : 0
-    const keepLo = preserveBottomBoundary
-
-    for (let r = 0; r < rows; r++) {
-      if (r > hi) newCol[r] = { type: 'full' }
-      else if (r === hi) newCol[r] = col[r]
-      else if (keepLo && r === lo) newCol[r] = col[r]
-      else if (r >= airFrom) newCol[r] = null
-      else newCol[r] = { type: 'full' }
-    }
-    return newCol
-  })
-
-  return { width, height: rows, columns }
+  // count === 2
+  if (tl && tr) return useSlabs ? { type: 'slab', half: 'top' } : { type: 'full' }
+  if (bl && br) return useSlabs ? { type: 'slab', half: 'bottom' } : { type: 'full' }
+  // left/right split or diagonal split: no single-block shape represents this cleanly
+  return { type: 'full' }
 }
 
 export function generateShape(opts: GenerateOptions): Shape {
   const width = Math.max(1, Math.round(opts.width))
   const height = Math.max(1, Math.round(opts.height))
-  const hole = generateHoleShape(width, height, opts.mode, opts.useSlabs, opts.useStairs)
-  return invertToWall(hole, width, opts.mode === 'oval')
+  const { mode, useSlabs, useStairs } = opts
+
+  const a = width / 2
+  const b = mode === 'oval' ? height / 2 : height
+  const centerOffsetX = (width - 1) / 2
+  const useSubSampling = useSlabs || useStairs
+
+  const columns: Column[] = []
+  for (let i = 0; i < width; i++) {
+    const cx = i - centerOffsetX
+    const col: Column = []
+
+    for (let r = 0; r < height; r++) {
+      const cy = rowCenterY(r, mode, height)
+
+      if (!useSubSampling) {
+        col.push(insideOpening(cx, cy, a, b) ? null : { type: 'full' })
+        continue
+      }
+
+      const leftX = cx - 0.25
+      const rightX = cx + 0.25
+      const bottomY = cy - 0.25
+      const topY = cy + 0.25
+
+      const tl = !insideOpening(leftX, topY, a, b)
+      const tr = !insideOpening(rightX, topY, a, b)
+      const bl = !insideOpening(leftX, bottomY, a, b)
+      const br = !insideOpening(rightX, bottomY, a, b)
+
+      col.push(classifyCell(tl, tr, bl, br, useSlabs, useStairs))
+    }
+    columns.push(col)
+  }
+
+  return { width, height, columns }
 }
 
 export interface Summary {