fix(🐛): fix bugs in atan2() (#244)

wcandillon · Apr 27, 2020 · 4c495ce · 4c495ce
1 parent 5e0b7c3
commit 4c495ce
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Showing 3 changed files with 30 additions and 12 deletions.
diff --git a/packages/core/src/Math.ts b/packages/core/src/Math.ts
@@ -4,6 +4,7 @@ const {
   eq,
   set,
   cond,
+  atan,
   add,
   multiply,
   lessThan,
@@ -89,17 +90,28 @@ export const toDeg = proc(
 // https://en.wikipedia.org/wiki/Atan2
 // https://www.gamedev.net/forums/topic/441464-manually-implementing-atan2-or-atan/
 // https://developer.download.nvidia.com/cg/atan2.html
+// https://www.medcalc.org/manual/atan2_function.php
 export const atan2 = proc(
   (y: Animated.Adaptable<number>, x: Animated.Adaptable<number>) => {
-    const coeff1 = Math.PI / 4;
-    const coeff2 = 3 * coeff1;
-    const absY = abs(y);
-    const angle = cond(
-      greaterOrEq(x, 0),
-      [sub(coeff1, multiply(coeff1, divide(sub(x, absY), add(x, absY))))],
-      [sub(coeff2, multiply(coeff1, divide(add(x, absY), sub(absY, x))))]
+    const a = atan(divide(y, x));
+    const { PI } = Math;
+    return cond(
+      greaterThan(x, 0),
+      a,
+      cond(
+        and(lessThan(x, 0), greaterOrEq(y, 0)),
+        add(a, PI),
+        cond(
+          and(lessThan(x, 0), lessThan(y, 0)),
+          sub(a, PI),
+          cond(
+            and(eq(x, 0), greaterThan(y, 0)),
+            PI / 2,
+            cond(and(eq(x, 0), lessThan(y, 0)), -PI / 2, 0)
+          )
+        )
+      )
     );
-    return cond(lessThan(y, 0), multiply(angle, -1), cond(eq(y, 0), 0, angle));
   }
 );
 

diff --git a/packages/core/src/__tests__/Coordinates.test.ts b/packages/core/src/__tests__/Coordinates.test.ts
@@ -56,13 +56,13 @@ test("cartesian2Polar 1", () => {
   const y = 100;
   const center = { x: 100, y: 100 };
   const { theta, radius } = cartesian2Polar(canvas2Cartesian({ x, y }, center));
-  expect(theta[" __value"]).toBe(0);
+  expect(theta[" __value"]).toBe(Math.PI);
   expect(radius[" __value"]).toBe(100);
   const { x: x1, y: y1 } = cartesian2Canvas(
     polar2Cartesian({ theta, radius }),
     center
   );
-  expect(x1[" __value"]).toBe(200);
+  expect(x1[" __value"]).toBe(0);
   expect(Math.round(y1[" __value"])).toBe(100);
 });
 
@@ -71,12 +71,12 @@ test("cartesian2Polar 2", () => {
   const y = 100;
   const center = { x: 100, y: 100 };
   const { theta, radius } = canvas2Polar({ x, y }, center);
-  expect(theta[" __value"]).toBe(0);
+  expect(theta[" __value"]).toBe(Math.PI);
   expect(radius[" __value"]).toBe(100);
   const { x: x1, y: y1 } = polar2Canvas(
     { theta, radius },
     { x: radius, y: radius }
   );
-  expect(x1[" __value"]).toBe(200);
+  expect(x1[" __value"]).toBe(0);
   expect(Math.round(y1[" __value"])).toBe(100);
 });
diff --git a/packages/core/src/__tests__/Math.test.ts b/packages/core/src/__tests__/Math.test.ts
@@ -7,6 +7,12 @@ test("atan2()", () => {
   expect(atan2(0, 0)[" __value"]).toBe(Math.atan2(0, 0));
   expect(atan2(0, 100)[" __value"]).toBe(Math.atan2(0, 100));
   expect(atan2(100, 0)[" __value"]).toBe(Math.atan2(100, 0));
+  expect(atan2(50, 25)[" __value"]).toBe(Math.atan2(50, 25));
+  expect(atan2(25, 50)[" __value"]).toBe(Math.atan2(25, 50));
+  expect(atan2(-1, 0)[" __value"]).toBe(Math.atan2(-1, 0));
+  expect(atan2(-3, -4)[" __value"]).toBe(Math.atan2(-3, -4));
+  expect(atan2(0, 3)[" __value"]).toBe(Math.atan2(0, 3));
+  expect(atan2(0, -3)[" __value"]).toBe(Math.atan2(0, -3));
 });
 
 test("round()", () => {