fix: ctx.globalAlpha should effect drawImage (#561)

__test__/regression.spec.ts

@@ -83,7 +83,7 @@ test('transform-with-radial-gradient-x', async (t) => {
   await snapshotImage(t, { canvas, ctx })
 })
 
-test('global-alpha-should-not-effect-drawImage', async (t) => {
+test('fill-alpha-should-not-effect-drawImage', async (t) => {
   const canvas = createCanvas(300, 320)
   const ctx = canvas.getContext('2d')
   ctx.fillStyle = 'rgba(3, 169, 244, 0.5)'
@@ -93,3 +93,14 @@ test('global-alpha-should-not-effect-drawImage', async (t) => {
   ctx.drawImage(await loadImage(image), 0, 0, 200, 100)
   await snapshotImage(t, { ctx, canvas })
 })
+
+test('global-alpha-should-effect-drawImage', async (t) => {
+  const canvas = createCanvas(300, 320)
+  const ctx = canvas.getContext('2d')
+  ctx.globalAlpha = 0.2
+
+  // Image
+  const image = await fs.readFile(join(__dirname, 'javascript.png'))
+  ctx.drawImage(await loadImage(image), 0, 0, 200, 100)
+  await snapshotImage(t, { ctx, canvas }, 'png', 1)
+})

src/ctx.rs

@@ -836,7 +836,7 @@ impl CanvasRenderingContext2D {
       );
       return;
     }
-
+    self.context.state.global_alpha = alpha;
     self.context.state.paint.set_alpha((alpha * 255.0) as u8);
   }