Respect LayerSettings::alpha in Skia-RE for buffer layers

Test: Manual. Open notification. Check whether the alpha of
      the shade is correct.
Bug: 173418499
Change-Id: I768fe3046bbcce3ab3156a0ced9fc14f34f4f1bc
diff --git a/libs/renderengine/skia/SkiaGLRenderEngine.cpp b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
index aefedb4..032e9b9 100644
--- a/libs/renderengine/skia/SkiaGLRenderEngine.cpp
+++ b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
@@ -678,6 +678,8 @@
             } else {
                 paint.setShader(shader);
             }
+            // Make sure to take into the account the alpha set on the layer.
+            paint.setAlphaf(layer->alpha);
         } else {
             ATRACE_NAME("DrawColor");
             const auto color = layer->source.solidColor;
@@ -824,7 +826,7 @@
     ATRACE_CALL();
 
     SkPaint paint;
-    paint.setAlpha(static_cast<int>(effectRegion.alpha * 255));
+    paint.setAlphaf(effectRegion.alpha);
     const auto matrix = mBlurFilter->getShaderMatrix();
     paint.setShader(blurredSurface->makeImageSnapshot()->makeShader(matrix));