add new snippet 'hourglass'; revision of 'help.htm'

snippets/busy-hourglass/qml/ext/Hourglass.qml

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+import QtQuick 2.15
+
+Rectangle {
+  anchors.fill: parent
+  visible: animation.running
+
+  Image {
+    id: hourglass1
+    anchors.centerIn: parent
+    width: 40
+    fillMode: Image.PreserveAspectFit
+    source: "../img/hourglass.png"
+  }
+
+  Image {
+    id: hourglass2
+    anchors.centerIn: parent
+    width: hourglass1.width
+    fillMode: Image.PreserveAspectFit
+    source: "../img/hourglass.png"
+    opacity: 0
+  }
+
+  SequentialAnimation {
+    id: animation
+    objectName: "hourglass"
+    loops: Animation.Infinite
+
+    RotationAnimation { target: hourglass1; from: 0; to: 180; duration: 1000; easing.type: Easing.InOutSine }
+
+    ParallelAnimation {
+      NumberAnimation { target: hourglass1; property: "opacity"; from: 1; to: 0; duration: 1500; easing.type: Easing.InOutSine }
+      NumberAnimation { target: hourglass2; property: "opacity"; from: 0; to: 1; duration: 1500; easing.type: Easing.InOutSine }
+    }
+
+    // reset
+    NumberAnimation { target: hourglass1; property: "opacity"; to: 1; duration: 0 }
+    NumberAnimation { target: hourglass2; property: "opacity"; to: 0; duration: 0 }
+  }
+}

snippets/busy-hourglass/qml/main.qml

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+import QtQuick 2.15
+import 'ext/' as Ext
+
+Rectangle {
+  width: 300
+  height: 500
+
+  Ext.Hourglass {}
+}

snippets/busy-hourglass/readme.md

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+Description
+-----------
+
+An hourglass animation (written in QML) during a long activity running in
+a thread.

snippets/busy-hourglass/run.lisp

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+(in-package :qml-user)
+
+(defun load-huge-library ()
+  (q> |running| "hourglass" t)         ; start animation
+  ;; run task in thread
+  (mp:process-run-function
+   :loading
+   (lambda ()
+     (sleep 10) ; loading patiently...
+     (q> |running| "hourglass" nil)))) ; stop animation
+
+(qsingle-shot 1000 'load-huge-library)