Fixed backface visibility. (cypress-io#5591)

sainthkh · flotwig · commit ab8957a3ba35 · 2019-11-08T15:49:56.000-05:00
* Fixed backface visibility.

* Show reason.

* Reorganized logic.
diff --git a/packages/driver/src/dom/visibility.js b/packages/driver/src/dom/visibility.js
@@ -61,6 +61,10 @@ const isHidden = (el, name = 'isHidden()') => {
     return true // is hidden
   }
 
+  if (elIsBackface($el)) {
+    return true
+  }
+
   // we do some calculations taking into account the parents
   // to see if its hidden by a parent
   if (elIsHiddenByAncestors($el)) {
@@ -112,6 +116,40 @@ const elHasVisibilityHidden = ($el) => {
   return $el.css('visibility') === 'hidden'
 }
 
+const numberRegex = /-?[0-9]+(?:\.[0-9]+)?/g
+// This is a simplified version of backface culling.
+// https://en.wikipedia.org/wiki/Back-face_culling
+//
+// We defined view normal vector, (0, 0, -1), - eye to screen.
+// and default normal vector, (0, 0, 1)
+// When dot product of them are >= 0, item is visible.
+const elIsBackface = ($el) => {
+  const el = $el[0]
+  const style = getComputedStyle(el)
+  const backface = style.getPropertyValue('backface-visibility')
+  const backfaceInvisible = backface === 'hidden'
+  const transform = style.getPropertyValue('transform')
+
+  if (!backfaceInvisible || !transform.startsWith('matrix3d')) {
+    return false
+  }
+
+  const m3d = transform.substring(8).match(numberRegex)
+  const defaultNormal = [0, 0, -1]
+  const elNormal = findNormal(m3d)
+  // Simplified dot product.
+  // [0] and [1] are always 0
+  const dot = defaultNormal[2] * elNormal[2]
+
+  return dot >= 0
+}
+
+const findNormal = (m) => {
+  const length = Math.sqrt(+m[8] * +m[8] + +m[9] * +m[9] + +m[10] * +m[10])
+
+  return [+m[8] / length, +m[9] / length, +m[10] / length]
+}
+
 const elHasVisibilityCollapse = ($el) => {
   return $el.css('visibility') === 'collapse'
 }
@@ -272,6 +310,10 @@ const elIsHiddenByAncestors = function ($el, $origEl = $el) {
     return !elDescendentsHavePositionFixedOrAbsolute($parent, $origEl)
   }
 
+  if (elIsBackface($parent)) {
+    return true
+  }
+
   // continue to recursively walk up the chain until we reach body or html
   return elIsHiddenByAncestors($parent, $origEl)
 }
@@ -388,6 +430,10 @@ const getReasonIsHidden = function ($el) {
     return `This element '${node}' is not visible because it has an effective width and height of: '${width} x ${height}' pixels.`
   }
 
+  if (elIsBackface($el)) {
+    return `This element '${node}' is not visible because it is rotated and its backface is hidden.`
+  }
+
   if ($parent = parentHasNoOffsetWidthOrHeightAndOverflowHidden($el.parent())) {
     parentNode = $elements.stringify($parent, 'short')
     width = elOffsetWidth($parent)
diff --git a/packages/driver/test/cypress/integration/dom/visibility_spec.js b/packages/driver/test/cypress/integration/dom/visibility_spec.js
@@ -820,12 +820,53 @@ describe('src/cypress/dom/visibility', () => {
     })
 
     describe('css backface-visibility', () => {
+      describe('element visibility by backface-visibility and rotation', () => {
+        const add = (el) => {
+          return $(el).appendTo(cy.$$('body'))
+        }
+
+        it('is visible when there is no transform', () => {
+          const el = add('<div>No transform</div>')
+
+          expect(el).to.be.visible
+        })
+
+        it('is visible when an element is rotated < 90 degrees', () => {
+          const el = add('<div style="backface-visibility: hidden; transform: rotateX(45deg)">rotateX(45deg)</div>')
+
+          expect(el).to.be.visible
+
+          const el2 = add('<div style="backface-visibility: hidden; transform: rotateY(-45deg)">rotateY(-45deg)</div>')
+
+          expect(el2).to.be.visible
+        })
+
+        it('is invisible when an element is rotated > 90 degrees', () => {
+          const el = add('<div style="backface-visibility: hidden; transform: rotateX(135deg)">rotateX(135deg)</div>')
+
+          expect(el).to.be.hidden
+
+          const el2 = add('<div style="backface-visibility: hidden; transform: rotateY(-135deg)">rotateY(-135deg)</div>')
+
+          expect(el2).to.be.hidden
+        })
+
+        it('is invisible when an element is rotated in 90 degrees', () => {
+          const el = add('<div style="backface-visibility: hidden; transform: rotateX(90deg)">rotateX(90deg)</div>')
+
+          expect(el).to.be.hidden
+
+          const el2 = add('<div style="backface-visibility: hidden; transform: rotateY(-90deg)">rotateY(-90deg)</div>')
+
+          expect(el2).to.be.hidden
+        })
+      })
+
       it('is visible when backface not visible', function () {
         expect(this.$parentsWithBackfaceVisibilityHidden.find('#front')).to.be.visible
       })
 
-      // TODO: why is this skipped?
-      it.skip('is hidden when backface visible', function () {
+      it('is hidden when backface visible', function () {
         expect(this.$parentsWithBackfaceVisibilityHidden.find('#back')).to.be.hidden
       })
     })
