Retrieve a list of composition settings from front end layer

Replace prepareClientComposition and prepareShadowClientComposition
calls with one that provides a list of composition settings in z-order
to handle layers that renders shadows wihtout any content.
If the EffectLayer is called with an invalid color, skip the color fill.

Test: atest libcompositionengine_test
Test: LayerTransactionTest.SetFlagsSecureEUidSystem
Test: go/wm-smoke
Change-Id: Iad16931341fc2e58247f4439a322c0ad1e8750f8
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 8eb5c22..5073a92 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -492,13 +492,12 @@
     compositionState->hasProtectedContent = isProtected();
 
     const bool usesRoundedCorners = getRoundedCornerState().radius != 0.f;
-    const bool drawsShadows = mEffectiveShadowRadius != 0.f;
 
     compositionState->isOpaque =
             isOpaque(drawingState) && !usesRoundedCorners && getAlpha() == 1.0_hf;
 
     // Force client composition for special cases known only to the front-end.
-    if (isHdrY410() || usesRoundedCorners || drawsShadows) {
+    if (isHdrY410() || usesRoundedCorners || drawShadows()) {
         compositionState->forceClientComposition = true;
     }
 }
@@ -653,6 +652,49 @@
     return shadowLayer;
 }
 
+void Layer::prepareClearClientComposition(LayerFE::LayerSettings& layerSettings,
+                                          bool blackout) const {
+    layerSettings.source.buffer.buffer = nullptr;
+    layerSettings.source.solidColor = half3(0.0, 0.0, 0.0);
+    layerSettings.disableBlending = true;
+    layerSettings.frameNumber = 0;
+
+    // If layer is blacked out, force alpha to 1 so that we draw a black color layer.
+    layerSettings.alpha = blackout ? 1.0f : 0.0f;
+}
+
+std::vector<compositionengine::LayerFE::LayerSettings> Layer::prepareClientCompositionList(
+        compositionengine::LayerFE::ClientCompositionTargetSettings& targetSettings) {
+    std::optional<compositionengine::LayerFE::LayerSettings> layerSettings =
+            prepareClientComposition(targetSettings);
+    // Nothing to render.
+    if (!layerSettings) {
+        return {};
+    }
+
+    // HWC requests to clear this layer.
+    if (targetSettings.clearContent) {
+        prepareClearClientComposition(*layerSettings, false /* blackout */);
+        return {*layerSettings};
+    }
+
+    std::optional<compositionengine::LayerFE::LayerSettings> shadowSettings =
+            prepareShadowClientComposition(*layerSettings, targetSettings.viewport,
+                                           targetSettings.dataspace);
+    // There are no shadows to render.
+    if (!shadowSettings) {
+        return {*layerSettings};
+    }
+
+    // If the layer casts a shadow but the content casting the shadow is occluded, skip
+    // composing the non-shadow content and only draw the shadows.
+    if (targetSettings.realContentIsVisible) {
+        return {*shadowSettings, *layerSettings};
+    }
+
+    return {*shadowSettings};
+}
+
 Hwc2::IComposerClient::Composition Layer::getCompositionType(
         const sp<const DisplayDevice>& display) const {
     const auto outputLayer = findOutputLayerForDisplay(display);