Add a smooth corner painter works better with rectangles with a larger aspect ratio

index.html

@@ -28,6 +28,7 @@
       }
 
       .box,
+      .rect,
       p {
         display: grid;
         place-items: center;
@@ -39,6 +40,12 @@
         color: #fff;
       }
 
+      .rect {
+        width: 10rem;
+        height: 30rem;
+        color: #fff;
+      }
+
       .avatar {
         width: 10rem;
         height: 10rem;
@@ -50,7 +57,8 @@
 
       .box,
       .avatar,
-      .poster {
+      .poster,
+      .rect {
         flex-shrink: 0;
         object-fit: cover;
         object-position: 50% 100%;
@@ -62,6 +70,42 @@
         -webkit-mask-image: paint(smooth-corners);
       }
 
+      .mask-v2 {
+        background: linear-gradient(#f34072, #d01257);
+        mask-image: paint(smooth-corners-v2);
+        -webkit-mask-image: paint(smooth-corners-v2);
+      }
+
+      .v2-5-1 {
+        --smooth-corners: 5;
+        --smooth-corners-radius: 1rem;
+        --smooth-corners-steps: 360;
+      }
+
+      .v2-5-1d5 {
+        --smooth-corners: 5;
+        --smooth-corners-radius: 1.5rem;
+        --smooth-corners-steps: 360;
+      }
+
+      .v2-5-0d5 {
+        --smooth-corners: 5;
+        --smooth-corners-radius: 0.5rem;
+        --smooth-corners-steps: 360;
+      }
+
+      .v2-4-1 {
+        --smooth-corners: 4;
+        --smooth-corners-radius: 1rem;
+        --smooth-corners-steps: 360;
+      }
+
+      .v2-2-1 {
+        --smooth-corners: 2;
+        --smooth-corners-radius: 1rem;
+        --smooth-corners-steps: 360;
+      }
+
       .square {
         --smooth-corners: 5;
       }
@@ -323,6 +367,28 @@
       </div>
     </section>
     <hr />
+    <section>
+      <p style="width:100%;">Update: add a smooth corner painter that better supports rectangle.</p>
+    </section>
+    <section>
+      <div>
+        <p>Original</p>
+        <img
+        src='https://media.kitsu.io/anime/poster_images/42722/large.jpg?1580402011'
+        class='rect mask v2-5-1'
+        />
+      </div>
+      <div>
+        <p>V2</p>
+        <img
+        src='https://media.kitsu.io/anime/poster_images/42722/large.jpg?1580402011'
+        class='rect mask-v2 v2-5-1'
+        />
+      </div>
+      <div class="rect mask-v2 v2-5-1">V2 5 R1</div>
+      <div class="rect mask-v2 v2-4-1">V2 4</div>
+      <div class="rect mask-v2 v2-2-1">V2 5</div>
+    </section>
     <!-- Gradient -->
     <section>
       <div class='box special-16-2 mask'>16, 2</div>

paint.js

@@ -55,7 +55,83 @@ class SmoothCornersPainter {
     ctx.closePath()
     ctx.fill()
   }
+}
+
+class SmoothCornerPainterV2 {
+  static get inputProperties() {
+    return ['--smooth-corners', '--smooth-corners-radius', '--smooth-corners-steps']
+  }
+
+
+  superellipse(a, b, nX = 4, nY, steps = 360) {
+    if (Number.isNaN(nX)) nX = 4
+    if (typeof nY === 'undefined' || Number.isNaN(nY)) nY = nX
+    if (nX > 100) nX = 100
+    if (nY > 100) nY = 100
+    if (nX < 0.00000000001) nX = 0.00000000001
+    if (nY < 0.00000000001) nY = 0.00000000001
+
+    const nX2 = 2 / nX
+    const nY2 = nY ? 2 / nY : nX2
+    const step = (2 * Math.PI) / steps
+    const points = t => {
+      const cosT = Math.cos(t)
+      const sinT = Math.sin(t)
+      return {
+        x: Math.abs(cosT) ** nX2 * a * Math.sign(cosT),
+        y: Math.abs(sinT) ** nY2 * b * Math.sign(sinT)
+      }
+    }
+    return Array.from({ length: steps }, (_, i) => points(i * step))
+  }
+
+  paint(ctx, size, props) {
+
+    const [nX, nY] = props
+      .get('--smooth-corners')
+      .toString()
+      .replace(/ /g, '')
+      .split(',')
+      .map(parseFloat)
+
+    const halfWidth = size.width / 2
+    const halfHeight = size.height / 2
+    const cornerRadius = Math.min(parseFloat(props.get('--smooth-corner-radius')) || size.width / 2, size.height / 2, size.width / 2)
+    const steps = parseFloat(props.get('--smooth-corner-steps')) || 360
+    const smoothCorners = this.superellipse(
+      cornerRadius,
+      cornerRadius,
+      nX,
+      nY,
+      steps
+    )
+
+    const xOffset = halfWidth - cornerRadius
+    const yOffset = halfHeight - cornerRadius
+
+    const leftBottomCorners = smoothCorners.slice(0, steps / 4).map(({ x, y }) => ({ x: x + xOffset, y: y + yOffset }))
+    const rightBottomCorners = smoothCorners.slice(steps / 4, steps / 2).map(({ x, y }) => ({ x: x - xOffset, y: y + yOffset }))
+    const rightTopCorners = smoothCorners.slice(steps / 2, steps * 3 / 4).map(({ x, y }) => ({ x: x - xOffset, y: y - yOffset }))
+    const leftTopCorners = smoothCorners.slice(steps * 3 / 4, steps).map(({ x, y }) => ({ x: x + xOffset, y: y - yOffset }))
+    const points = [...leftBottomCorners, ...rightBottomCorners, ...rightTopCorners, ...leftTopCorners]
+
+    ctx.fillStyle = '#000'
+    ctx.setTransform(1, 0, 0, 1, halfWidth, halfHeight)
+    ctx.beginPath()
+    points.forEach(({ x, y }, i) => {
+      if (i === 0) ctx.moveTo(x, y)
+      else ctx.lineTo(x, y)
+    })
+    ctx.closePath()
+    ctx.fill()
+
+  }
+
+
+
+
 }
 
 // eslint-disable-next-line no-undef
 registerPaint('smooth-corners', SmoothCornersPainter)
+registerPaint('smooth-corners-v2', SmoothCornerPainterV2)