android相机热启动缓存帧解决方案（任务快照）

摘要：android APP的启动方式主要分为两种：冷启动和热启动。冷启动会把LOGO当作启动页面；热启动则会把任务快照当作启动页面。相机作为实时获取预览图像的应用，在热启动时就会存在一个问题：前一次退出的预览画面会被存储为任务快照，下一次热启动时，会先显示之前退出时被保存的任务快照，当预览准备好后，刷新预览数据，这就会有一种跳帧的现象。本文通过目前行业机的通用处理方式，将相机的任务快照进行蒙层虚化（模糊）处理，提升用户体验感。

一、准备知识

android冷启动为什么会自动把LOGO当做启动页面

应用启动时间（android developers）

任务快照（android source）

二、代码实现

目标平台：MTK android 13

方案：在获取任务快照snapshotTask中，填充buffer之前将获取到的buffer内容进行模糊处理。

Index: frameworks/base/services/core/java/com/android/server/wm/TaskSnapshotController.java
===================================================================
--- frameworks/base/services/core/java/com/android/server/wm/TaskSnapshotController.java	(revision B)
+++ frameworks/base/services/core/java/com/android/server/wm/TaskSnapshotController.java	(revision A)
@@ -38,13 +38,16 @@
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
 import android.graphics.Color;
+import android.graphics.ColorSpace;
 import android.graphics.Paint;
 import android.graphics.PixelFormat;
 import android.graphics.Point;
 import android.graphics.RecordingCanvas;
 import android.graphics.Rect;
+import android.graphics.RenderEffect;
 import android.graphics.RenderNode;
 import android.hardware.HardwareBuffer;
+import android.os.Build;
 import android.os.Environment;
 import android.os.Handler;
 import android.util.ArraySet;
@@ -512,11 +515,73 @@
             // Failed to acquire image. Has been logged.
             return null;
         }
-        builder.setSnapshot(screenshotBuffer.getHardwareBuffer());
+        String targetPackage = task.getTopMostActivity().mActivityComponent.getPackageName();
+        if ("com.mediatek.camera".equals(targetPackage)) {
+            Slog.d("TaskSnapshotController", "snapshotTask::mtk cam snapshot");
+            builder.setSnapshot(applyBlurToBuffer(screenshotBuffer.getHardwareBuffer(), screenshotBuffer.getColorSpace()));
+        } else {
+            builder.setSnapshot(screenshotBuffer.getHardwareBuffer());
+        }
         builder.setColorSpace(screenshotBuffer.getColorSpace());
         return builder.build();
     }
 
+    private HardwareBuffer applyBlurToBuffer(HardwareBuffer originalBuffer,
+                                             ColorSpace colorSpace) {
+        // Only RGBA format is supported
+        if (originalBuffer.getFormat() != HardwareBuffer.RGBA_8888 &&
+            originalBuffer.getFormat() != HardwareBuffer.RGBA_FP16) {
+            Slog.w("TaskSnapshotController", "Unsupported buffer format for blur: " + originalBuffer.getFormat());
+            return originalBuffer;
+        }
+
+        int width = originalBuffer.getWidth();
+        int height = originalBuffer.getHeight();
+        if (width <= 1 || height <= 1) return originalBuffer;
+
+        // Packaging the original HardwareBuffer as a Bitmap (without copying pixels)
+        Bitmap srcBitmap = Bitmap.wrapHardwareBuffer(originalBuffer, colorSpace);
+        if (srcBitmap == null) return originalBuffer;
+
+        try {
+            RenderNode node = RenderNode.create("BlurLayer", null);
+            node.setLeftTopRightBottom(0, 0, width, height);
+            RecordingCanvas canvas = node.start(width, height);
+
+            // Draw the original image
+            canvas.drawBitmap(srcBitmap, 0, 0, null);
+
+            // Apply Gaussian blur effect (API 31+)
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+                RenderEffect blurEffect = RenderEffect.createBlurEffect(
+                        25f, 25f, android.graphics.Shader.TileMode.CLAMP);
+                node.setRenderEffect(blurEffect);
+            } else {
+                // The low version cannot be blurred, and the original buffer is returned directly
+                srcBitmap.recycle();
+                return originalBuffer;
+            }
+
+            node.end(canvas);
+
+            // Generate new HardwareBuffer
+            Bitmap blurredBitmap = ThreadedRenderer.createHardwareBitmap(node, width, height);
+            srcBitmap.recycle(); // Release the temporary Bitmap (without closing the original buffer)
+
+            if (blurredBitmap == null) {
+                return originalBuffer;
+            }
+
+            HardwareBuffer blurredBuffer = blurredBitmap.getHardwareBuffer();
+            blurredBitmap.recycle(); // The Bitmap wrapper is released, but its internal buffer is still referenced
+            return blurredBuffer != null ? blurredBuffer : originalBuffer;
+
+        } catch (Exception e) {
+            Slog.e("TaskSnapshotController", "Failed to apply blur to buffer", e);
+            return originalBuffer;
+        }
+    }
+
     void setTaskSnapshotEnabled(boolean enabled) {
         mTaskSnapshotEnabled = enabled;
     }