Don't show the background if Button.flat

Summary: Otherwise the flat property is ignored

Test Plan: Tested on KDE Connect port to use PlasmaComponents

Reviewers: #plasma, mart

Reviewed By: #plasma, mart

Subscribers: mart, #frameworks

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D11652

src/declarativeimports/plasmacomponents3/Button.qml

@@ -52,6 +52,7 @@ T.Button {
         implicitHeight: units.gridUnit * 1.6
         Private.ButtonShadow {
             anchors.fill: parent
+            visible: (!control.flat || control.hovered) && (!control.pressed || !control.checked)
             state: {
                 if (control.pressed) {
                     return "hidden"
@@ -69,7 +70,7 @@ T.Button {
             anchors.fill: parent
             imagePath: "widgets/button"
             prefix: "normal"
-            opacity: control.checked || control.pressed ? 0 : 1
+            opacity: (!control.flat || control.hovered) && (!control.pressed || !control.checked) ? 1 : 0
             Behavior on opacity {
                 OpacityAnimator {
                     duration: units.longDuration

tests/buttons_pc3.0.qml

@@ -0,0 +1,28 @@
+import QtQuick 2.0
+
+import org.kde.plasma.components 3.0 as PlasmaComponents
+
+Rectangle
+{
+    width: 500
+    height: 300
+    color: "white"
+
+    Flow {
+        anchors.fill: parent
+        anchors.margins: 20
+        spacing: 20
+
+        PlasmaComponents.Button {
+            text: "test"
+        }
+        PlasmaComponents.Button {
+            text: "test"
+            flat: true
+        }
+        PlasmaComponents.ToolButton {
+            text: "test"
+        }
+    }
+}
+