fix issue #500 View.toBitmap should take scroll state into consideration (#504)

* fix issue #500 View.toBitmap should take scroll state into consideration

* add toBitmapScrolls test case

* hardcode test string

* remove canvas save/restore
simple bitmap compare

* format file header

Author: LanderlYoung

src/androidTest/java/androidx/core/view/ViewTest.kt

@@ -17,7 +17,9 @@
 package androidx.core.view
 
 import android.graphics.Bitmap
+import android.graphics.Color
 import android.support.test.InstrumentationRegistry
+import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import android.widget.LinearLayout
@@ -175,6 +177,29 @@ class ViewTest {
         assertSame(Bitmap.Config.RGB_565, bitmap.config)
     }
 
+    @Test
+    fun toBitmapScrolls() {
+        val scrollView = LayoutInflater.from(context)!!
+                .inflate(R.layout.test_bitmap_scrolls, null, false)
+
+        val size = 100
+
+        scrollView.measure(
+                View.MeasureSpec.makeMeasureSpec(size, View.MeasureSpec.EXACTLY),
+                View.MeasureSpec.makeMeasureSpec(size, View.MeasureSpec.EXACTLY))
+        scrollView.layout(0, 0, size, size)
+
+        val noScroll = scrollView.toBitmap()
+        assertEquals(Color.WHITE, noScroll.getPixel(0, 0))
+        assertEquals(Color.WHITE, noScroll.getPixel(size - 1, size - 1))
+
+        scrollView.scrollTo(0, size)
+        val scrolls = scrollView.toBitmap()
+
+        assertEquals(Color.BLACK, scrolls.getPixel(0, 0))
+        assertEquals(Color.BLACK, scrolls.getPixel(size - 1, size - 1))
+    }
+
     @Test fun isVisible() {
         view.isVisible = true
         assertTrue(view.isVisible)

src/androidTest/res/layout/test_bitmap_scrolls.xml

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2018 The Android Open Source Project
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~       http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:orientation="vertical"
+    android:layout_width="100px"
+    android:layout_height="100px"
+    android:scrollbars="none"
+    >
+
+    <LinearLayout
+        android:layout_width="100px"
+        android:layout_height="wrap_content"
+        android:orientation="vertical">
+
+        <View
+            android:layout_width="match_parent"
+            android:layout_height="100px"
+            android:background="@android:color/white" />
+
+        <View
+            android:layout_width="match_parent"
+            android:layout_height="100px"
+            android:background="@android:color/black" />
+
+    </LinearLayout>
+
+</ScrollView>

src/main/java/androidx/core/view/View.kt

@@ -196,7 +196,10 @@ fun View.toBitmap(config: Bitmap.Config = Bitmap.Config.ARGB_8888): Bitmap {
     if (!ViewCompat.isLaidOut(this)) {
         throw IllegalStateException("View needs to be laid out before calling toBitmap()")
     }
-    return Bitmap.createBitmap(width, height, config).applyCanvas(::draw)
+    return Bitmap.createBitmap(width, height, config).applyCanvas {
+        translate(-scrollX.toFloat(), -scrollY.toFloat())
+        draw(this)
+    }
 }
 
 /**