conference: only load avatars if visible

Wrap avatars in a Loader to avoid constantly querying the image provider
for remote video participants.

Change-Id: Ieca2457416dfd4c33fc3a960a1e36643ea1f11ef

src/avatarimageprovider.h

@@ -38,6 +38,11 @@ public:
     {
         Q_UNUSED(size)
 
+        if (requestedSize == QSize(0, 0)) {
+            qWarning() << Q_FUNC_INFO << "Image request has no dimensions";
+            return {};
+        }
+
         // the first string is the item uri and the second is a uid
         // that is used for trigger a reload of the underlying image
         // data and can be discarded at this point

src/mainview/components/ParticipantOverlay.qml

@@ -54,16 +54,11 @@ Item {
 
     function setAvatar(show, uri, isLocal) {
         if (!show)
-            avatar.visible = false
+            avatar.active = false
         else {
-            if (isLocal) {
+            avatar.mode_ = isLocal ? Avatar.Mode.Account : Avatar.Mode.Contact
-                avatar.mode = Avatar.Mode.Account
+            avatar.imageId_ = isLocal ? LRCInstance.currentAccountId : uri
-                avatar.imageId = LRCInstance.currentAccountId
+            avatar.active = true
-            } else {
-                avatar.mode = Avatar.Mode.Contact
-                avatar.imageId = uri
-            }
-            avatar.visible = true
         }
     }
 
@@ -167,22 +162,31 @@ Item {
         }
     }
 
-    Avatar {
+    Loader {
         id: avatar
 
         anchors.centerIn: parent
 
-        property real size: Math.min(parent.width / 2, parent.height / 2)
+        active: false
-        height:  size
-        width:  size
 
-        // round the avatar source size up to some nearest multiple
+        property real size_: Math.min(parent.width / 2, parent.height / 2)
-        readonly property real step: 96
+        height:  size_
-        property real imageSize: Math.floor((size + step - 1) / step) * step
+        width:  size_
-        sourceSize: Qt.size(imageSize, imageSize)
 
-        visible: false
+        property int mode_
-        showPresenceIndicator: false
+        property string imageId_
+
+        sourceComponent: Component {
+            Avatar {
+                // round the avatar source size up to some nearest multiple
+                readonly property real step: 96
+                property real size: Math.floor((size_ + step - 1) / step) * step
+                sourceSize: Qt.size(size, size)
+                mode: mode_
+                imageId: size_ ? imageId_ : ""
+                showPresenceIndicator: false
+            }
+        }
     }
 
     // Participant background and buttons for moderation