fix(modal): backdrop animation when backdropBreakpoint is 1 (#25430)

Resolves #25402

Author: sean-perkins

core/src/components/modal/utils.spec.ts

@@ -0,0 +1,11 @@
+import { getBackdropValueForSheet } from './utils';
+
+describe('getBackdropValueForSheet()', () => {
+  it('should return a valid integer when backdropBreakpoint is 1', () => {
+    /**
+     * Issue: https://github.com/ionic-team/ionic-framework/issues/25402
+     */
+    const backdropBreakpoint = 1;
+    expect(getBackdropValueForSheet(1, backdropBreakpoint)).toBe(0);
+  });
+});

core/src/components/modal/utils.ts

@@ -23,7 +23,15 @@ export const getBackdropValueForSheet = (x: number, backdropBreakpoint: number)
    *
    * This is simplified from:
    * m = (1 - 0) / (maxBreakpoint - backdropBreakpoint)
+   *
+   * If the backdropBreakpoint is 1, we return 0 as the
+   * backdrop is completely hidden.
+   *
    */
+  if (backdropBreakpoint === 1) {
+    return 0;
+  }
+
   const slope = 1 / (1 - backdropBreakpoint);
 
   /**