fix: Unwanted white gap between bar border and bar fill (chartjs#12094)

src/elements/element.bar.js

@@ -124,18 +124,29 @@ function addNormalRectPath(ctx, rect) {
   ctx.rect(rect.x, rect.y, rect.w, rect.h);
 }
 
-function inflateRect(rect, amount, refRect = {}) {
+function inflateRect(rect, amount, refRect = {}, snap = false) {
   const x = rect.x !== refRect.x ? -amount : 0;
   const y = rect.y !== refRect.y ? -amount : 0;
   const w = (rect.x + rect.w !== refRect.x + refRect.w ? amount : 0) - x;
   const h = (rect.y + rect.h !== refRect.y + refRect.h ? amount : 0) - y;
-  return {
+
+  const result = {
     x: rect.x + x,
     y: rect.y + y,
     w: rect.w + w,
     h: rect.h + h,
     radius: rect.radius
   };
+
+  if (snap) {
+    const dpr = (typeof window !== 'undefined' && window.devicePixelRatio) ? window.devicePixelRatio : 1;
+    result.x = Math.round(result.x * dpr) / dpr;
+    result.y = Math.round(result.y * dpr) / dpr;
+    result.w = Math.round(result.w * dpr) / dpr;
+    result.h = Math.round(result.h * dpr) / dpr;
+  }
+
+  return result;
 }
 
 export default class BarElement extends Element {
@@ -185,15 +196,15 @@ export default class BarElement extends Element {
 
     if (outer.w !== inner.w || outer.h !== inner.h) {
       ctx.beginPath();
-      addRectPath(ctx, inflateRect(outer, inflateAmount, inner));
+      addRectPath(ctx, inflateRect(outer, inflateAmount, inner, true));
       ctx.clip();
-      addRectPath(ctx, inflateRect(inner, -inflateAmount, outer));
+      addRectPath(ctx, inflateRect(inner, -inflateAmount, outer, true));
       ctx.fillStyle = borderColor;
       ctx.fill('evenodd');
     }
 
     ctx.beginPath();
-    addRectPath(ctx, inflateRect(inner, inflateAmount));
+    addRectPath(ctx, inflateRect(inner, inflateAmount, undefined, true));
     ctx.fillStyle = backgroundColor;
     ctx.fill();
 

test/specs/element.bar.tests.js

@@ -64,4 +64,70 @@ describe('Bar element tests', function() {
 
     expect(bar.getCenterPoint()).toEqual({x: 10, y: 7.5});
   });
+
+  describe('unwanted white gap fix', () => {
+    it('should not produce white gap when borderWidth > 0', () => {
+      var chart = window.acquireChart({
+        type: 'bar',
+        data: {
+          datasets: [{
+            data: [50],
+            backgroundColor: 'pink',
+            borderColor: 'pink',
+            borderWidth: 15,
+            borderSkipped: false,
+          }],
+          labels: []
+        },
+        options: {
+          elements: {
+            bar: {
+              inflateAmount: 0,
+            }
+          },
+        }
+      });
+
+      const meta = chart.getDatasetMeta(0);
+      const bar = meta.data[0];
+      const props = bar.getProps(['width', 'height', 'borderWidth'], true);
+
+      expect(props.borderWidth).toBe(15);
+      expect(props.width).toBeGreaterThan(props.borderWidth * 2);
+      expect(props.height).toBeGreaterThan(props.borderWidth * 2);
+    });
+
+    it('should handle borderRadius without creating a gap', () => {
+      var chart = window.acquireChart({
+        type: 'bar',
+        data: {
+          datasets: [{
+            data: [30],
+            backgroundColor: 'black',
+            borderColor: 'black',
+            borderWidth: 10,
+            borderRadius: 8,
+            borderSkipped: false,
+          }],
+          labels: []
+        },
+        options: {
+          elements: {
+            bar: {
+              inflateAmount: 0,
+            }
+          },
+        }
+      });
+
+      const meta = chart.getDatasetMeta(0);
+      const bar = meta.data[0];
+      const props = bar.getProps(['width', 'height', 'borderWidth', 'borderRadius'], true);
+
+      expect(props.borderWidth).toBe(10);
+      expect(props.borderRadius).toBe(8);
+      expect(props.width).toBeGreaterThan(props.borderRadius + props.borderWidth);
+      expect(props.height).toBeGreaterThan(props.borderRadius + props.borderWidth);
+    });
+  });
 });