Set window to transparent when screenshotting layer.

Set the screenshot to transparent instead of black. This allows the
system to draw a color behind without having to crop out the area that
may not be drawn into.

Bug: 76442549
Test: When going to recents, area not drawn from layers is now
transparent instead of black.
Test: Transaction_test#CaptureTransparent

Change-Id: Id535eb753d3d1cae82658cd33423ce588aaa62f8

5 files changed, 42 insertions, 5 deletions

diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index e844d115c2..61ce30ca86 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -281,7 +281,8 @@ public:
                               rotation) {}
     DisplayRenderArea(const sp<const DisplayDevice> device, Rect sourceCrop, uint32_t reqHeight,
                       uint32_t reqWidth, ISurfaceComposer::Rotation rotation)
-          : RenderArea(reqHeight, reqWidth, rotation), mDevice(device), mSourceCrop(sourceCrop) {}
+          : RenderArea(reqHeight, reqWidth, CaptureFill::OPAQUE, rotation), mDevice(device),
+                              mSourceCrop(sourceCrop) {}
 
     const Transform& getTransform() const override { return mDevice->getTransform(); }
     Rect getBounds() const override { return mDevice->getBounds(); }
diff --git a/services/surfaceflinger/RenderArea.cpp b/services/surfaceflinger/RenderArea.cpp
index 6225df134d..46ec8e68ba 100644
--- a/services/surfaceflinger/RenderArea.cpp
+++ b/services/surfaceflinger/RenderArea.cpp
@@ -2,6 +2,15 @@
 
 namespace android {
 
+float RenderArea::getCaptureFillValue(CaptureFill captureFill) {
+    switch(captureFill) {
+        case CaptureFill::CLEAR:
+            return 0.0f;
+        case CaptureFill::OPAQUE:
+        default:
+            return 1.0f;
+    }
+}
 /*
  * Checks that the requested width and height are valid and updates them to the render area
  * dimensions if they are set to 0
diff --git a/services/surfaceflinger/RenderArea.h b/services/surfaceflinger/RenderArea.h
index bf0707f13b..62a3d5b333 100644
--- a/services/surfaceflinger/RenderArea.h
+++ b/services/surfaceflinger/RenderArea.h
@@ -9,10 +9,15 @@
 namespace android {
 
 class RenderArea {
+
 public:
-    RenderArea(uint32_t reqHeight, uint32_t reqWidth,
+    enum class CaptureFill {CLEAR, OPAQUE};
+
+    static float getCaptureFillValue(CaptureFill captureFill);
+
+    RenderArea(uint32_t reqHeight, uint32_t reqWidth, CaptureFill captureFill,
                ISurfaceComposer::Rotation rotation = ISurfaceComposer::eRotateNone)
-          : mReqHeight(reqHeight), mReqWidth(reqWidth) {
+          : mReqHeight(reqHeight), mReqWidth(reqWidth), mCaptureFill(captureFill) {
         mRotationFlags = Transform::fromRotation(rotation);
     }
 
@@ -36,10 +41,13 @@ public:
 
     status_t updateDimensions();
 
+    CaptureFill getCaptureFill() const { return mCaptureFill; };
+
 private:
     uint32_t mReqHeight;
     uint32_t mReqWidth;
     Transform::orientation_flags mRotationFlags;
+    CaptureFill mCaptureFill;
 };
 
 } // namespace android
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 183c1eb07c..781a30ccf5 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -4597,7 +4597,7 @@ status_t SurfaceFlinger::captureLayers(const sp<IBinder>& layerHandleBinder,
     public:
         LayerRenderArea(SurfaceFlinger* flinger, const sp<Layer>& layer, const Rect crop,
                         int32_t reqWidth, int32_t reqHeight, bool childrenOnly)
-              : RenderArea(reqHeight, reqWidth),
+              : RenderArea(reqHeight, reqWidth, CaptureFill::CLEAR),
                 mLayer(layer),
                 mCrop(crop),
                 mFlinger(flinger),
@@ -4834,8 +4834,9 @@ void SurfaceFlinger::renderScreenImplLocked(const RenderArea& renderArea,
                                     renderArea.getRotationFlags());
     engine.disableTexturing();
 
+    const float alpha = RenderArea::getCaptureFillValue(renderArea.getCaptureFill());
     // redraw the screen entirely...
-    engine.clearWithColor(0, 0, 0, 1);
+    engine.clearWithColor(0, 0, 0, alpha);
 
     traverseLayers([&](Layer* layer) {
         if (filtering) layer->setFiltering(true);
diff --git a/services/surfaceflinger/tests/Transaction_test.cpp b/services/surfaceflinger/tests/Transaction_test.cpp
index 176c691c6a..a0f12f1438 100644
--- a/services/surfaceflinger/tests/Transaction_test.cpp
+++ b/services/surfaceflinger/tests/Transaction_test.cpp
@@ -2358,6 +2358,24 @@ TEST_F(ScreenCaptureTest, CaptureLayerChildOnly) {
     mCapture->expectChildColor(0, 0);
 }
 
+TEST_F(ScreenCaptureTest, CaptureTransparent) {
+    sp<SurfaceControl> child =
+            mComposerClient->createSurface(String8("Child surface"), 10, 10, PIXEL_FORMAT_RGBA_8888,
+                                           0, mFGSurfaceControl.get());
+
+    fillSurfaceRGBA8(child, 200, 200, 200);
+
+    SurfaceComposerClient::Transaction().show(child).apply(true);
+
+    auto childHandle = child->getHandle();
+
+    // Captures child
+    ScreenCapture::captureLayers(&mCapture, childHandle, {0, 0, 10, 20});
+    mCapture->expectColor(Rect(0, 0, 9, 9), {200, 200, 200, 255});
+    // Area outside of child's bounds is transparent.
+    mCapture->expectColor(Rect(0, 10, 9, 19), {0, 0, 0, 0});
+}
+
 
 // In the following tests we verify successful skipping of a parent layer,
 // so we use the same verification logic and only change how we mutate