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<h3><a name="toc">Contents</a></h3>
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<li class="level2"><a href="#the-needle-component">The Needle Component</a></li>
<li class="level2"><a href="#the-foreground-component">The Foreground Component</a></li>
<li class="level2"><a href="#the-tickmark-label-component">The Tickmark Label Component</a></li>
<li class="level2"><a href="#the-tickmark-component">The Tickmark Component</a></li>
<li class="level2"><a href="#the-minor-tickmark-component">The Minor Tickmark Component</a></li>
<li class="level2"><a href="#the-background-component">The Background Component</a></li>
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<h1 class="title">Styling CircularGauge</h1>
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<!-- $$$styling-circulargauge.html-description -->
<div class="descr"> <a name="details"></a>
<a name="styling-circulargauge-needle"></a><a name="the-needle-component"></a>
<h3 >The Needle Component</h3>
<p>The <a href="qml-qtquick-controls-styles-circulargaugestyle.html#needle-prop">needle</a> component is rotated around the gauge to represent the current value.</p>
<p>Starting from the default style, we'll add a very basic white needle:</p>
<pre class="qml"><span class="name">needle</span>: <span class="name">Rectangle</span> {
<span class="name">y</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.15</span>
<span class="name">implicitWidth</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.03</span>
<span class="name">implicitHeight</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.9</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
<span class="name">color</span>: <span class="string">"#e5e5e5"</span>
}</pre>
<p class="centerAlign"><img src="images/styling-circulargauge-needle-example.png" alt="" /></p><p>As mentioned in the documentation for <a href="qml-qtquick-controls-styles-circulargaugestyle.html">CircularGaugeStyle</a>, <code>implicitWidth</code> and <code>implicitHeight</code> properties need to be set. This is so that the needle can be positioned properly. We always scale items by the <a href="qml-qtquick-controls-styles-circulargaugestyle.html#outerRadius-prop">outerRadius</a> property of the style, ensuring the control resizes gracefully.</p>
<p>We offset the needle vertically so that its back sits beyond the knob.</p>
<a name="styling-circulargauge-foreground"></a><a name="the-foreground-component"></a>
<h3 >The Foreground Component</h3>
<p>We've now changed the needle, but the default knob is still there; let's replace it. The <a href="qml-qtquick-controls-styles-circulargaugestyle.html#foreground-prop">foreground</a> component defines the default knob, so we can specify our own by overriding it (note that we could also set it to <code>null</code> if we didn't want a foreground):</p>
<pre class="qml"><span class="name">foreground</span>: <span class="name">Item</span> {
<span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
<span class="name">width</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.2</span>
<span class="name">height</span>: <span class="name">width</span>
<span class="name">radius</span>: <span class="name">width</span> <span class="operator">/</span> <span class="number">2</span>
<span class="name">color</span>: <span class="string">"#e5e5e5"</span>
<span class="name">anchors</span>.centerIn: <span class="name">parent</span>
}
}</pre>
<p class="centerAlign"><img src="images/styling-circulargauge-knob-example.png" alt="" /></p><p>Firstly, we create a circle from the Rectangle item by setting the radius to be half the width (either width or height will work here; they are always equal in this case). We make it a child of the Item, because the foreground fills the gauge. We then center it within the Item.</p>
<p>We set the color of the knob to the same white that we used before.</p>
<a name="styling-circulargauge-tickmarklabel"></a><a name="the-tickmark-label-component"></a>
<h3 >The Tickmark Label Component</h3>
<p>Suppose we want to caution the user if the value displayed by the gauge goes above or below a certain range. We could present this range to the user in several ways:</p>
<ol class="A">
<li>Change the color of the tickmarks depending on <code>styleData.value</code></li>
<li>Add an image to the background</li>
<li>Draw it with <a href="../qtquick/qml-qtquick-canvas.html">Canvas</a></li>
</ol>
<p>We'll choose options 1 and 3, as they are more flexible than using an image.</p>
<p>Firstly, let's change the color of the three highest tickmark labels:</p>
<pre class="qml"><span class="name">tickmarkLabel</span>: <span class="name">Text</span> {
<span class="name">font</span>.pixelSize: <span class="name">Math</span>.<span class="name">max</span>(<span class="number">6</span>, <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.1</span>)
<span class="name">text</span>: <span class="name">styleData</span>.<span class="name">value</span>
<span class="name">color</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator">>=</span> <span class="number">80</span> ? <span class="string">"#e34c22"</span> : <span class="string">"#e5e5e5"</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
}</pre>
<p class="centerAlign"><img src="images/styling-circulargauge-tickmarkLabel-example.png" alt="tickmarkLabel" /></p><p>We also change the color of the rest of the labels to the same white that we used for the needle and knob.</p>
<a name="styling-circulargauge-tickmark"></a><a name="the-tickmark-component"></a>
<h3 >The Tickmark Component</h3>
<p>Now let's do the same for the three highest tickmarks:</p>
<pre class="qml"><span class="name">tickmark</span>: <span class="name">Rectangle</span> {
<span class="name">visible</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator"><</span> <span class="number">80</span> <span class="operator">||</span> <span class="name">styleData</span>.<span class="name">value</span> <span class="operator">%</span> <span class="number">10</span> <span class="operator">==</span> <span class="number">0</span>
<span class="name">implicitWidth</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.02</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
<span class="name">implicitHeight</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.06</span>
<span class="name">color</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator">>=</span> <span class="number">80</span> ? <span class="string">"#e34c22"</span> : <span class="string">"#e5e5e5"</span>
}</pre>
<p class="centerAlign"><img src="images/styling-circulargauge-tickmark-example.png" alt="tickmark" /></p><a name="styling-circulargauge-minortickmark"></a><a name="the-minor-tickmark-component"></a>
<h3 >The Minor Tickmark Component</h3>
<p>For the minor tickmarks, we'll only show those which are not higher than <code>80</code>:</p>
<pre class="qml"><span class="name">minorTickmark</span>: <span class="name">Rectangle</span> {
<span class="name">visible</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator"><</span> <span class="number">80</span>
<span class="name">implicitWidth</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.01</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
<span class="name">implicitHeight</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.03</span>
<span class="name">color</span>: <span class="string">"#e5e5e5"</span>
}</pre>
<p class="centerAlign"><img src="images/styling-circulargauge-minorTickmark-example.png" alt="minorTickmark" /></p><p>This is because we'll draw something between that range in the next section.</p>
<a name="styling-circulargauge-background"></a><a name="the-background-component"></a>
<h3 >The Background Component</h3>
<p>We'll display the range that indicates caution with an orange arc:</p>
<pre class="qml"><span class="keyword">function</span> <span class="name">degreesToRadians</span>(<span class="name">degrees</span>) {
<span class="keyword">return</span> <span class="name">degrees</span> <span class="operator">*</span> (<span class="name">Math</span>.<span class="name">PI</span> <span class="operator">/</span> <span class="number">180</span>);
}
<span class="name">background</span>: <span class="name">Canvas</span> {
<span class="name">onPaint</span>: {
var <span class="name">ctx</span> = <span class="name">getContext</span>(<span class="string">"2d"</span>);
<span class="name">ctx</span>.<span class="name">reset</span>();
<span class="name">ctx</span>.<span class="name">beginPath</span>();
<span class="name">ctx</span>.<span class="name">strokeStyle</span> <span class="operator">=</span> <span class="string">"#e34c22"</span>;
<span class="name">ctx</span>.<span class="name">lineWidth</span> <span class="operator">=</span> <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.02</span>;
<span class="name">ctx</span>.<span class="name">arc</span>(<span class="name">outerRadius</span>, <span class="name">outerRadius</span>, <span class="name">outerRadius</span> <span class="operator">-</span> <span class="name">ctx</span>.<span class="name">lineWidth</span> <span class="operator">/</span> <span class="number">2</span>,
<span class="name">degreesToRadians</span>(<span class="name">valueToAngle</span>(<span class="number">80</span>) <span class="operator">-</span> <span class="number">90</span>), <span class="name">degreesToRadians</span>(<span class="name">valueToAngle</span>(<span class="number">100</span>) <span class="operator">-</span> <span class="number">90</span>));
<span class="name">ctx</span>.<span class="name">stroke</span>();
}
}</pre>
<p>We define a function to convert degrees to radians, which are the units used by <a href="../qtquick/qml-qtquick-canvas.html">Canvas</a>.</p>
<p>Next, we do the drawing of the range using Canvas. We draw an arc between <code>80</code> and <code>100</code>, using the <a href="qml-qtquick-controls-styles-circulargaugestyle.html#valueToAngle-method">valueToAngle()</a> function provided by <a href="qml-qtquick-controls-styles-circulargaugestyle.html">CircularGaugeStyle</a>. Note that we subtract <code>90</code> degrees before converting to radians, as our origin is north and Canvas' is east.</p>
<p>The finished product:</p>
<p class="centerAlign"><img src="images/styling-circulargauge-background-example.png" alt="background" /></p><p>The complete code for this example is as follows:</p>
<pre class="qml">import QtQuick 2.0
import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
import QtQuick.Extras 1.4
import QtQuick.Extras.Private 1.0
<span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
<span class="name">width</span>: <span class="number">300</span>
<span class="name">height</span>: <span class="number">300</span>
<span class="name">color</span>: <span class="string">"#494d53"</span>
<span class="type">CircularGauge</span> {
<span class="name">id</span>: <span class="name">gauge</span>
<span class="name">anchors</span>.centerIn: <span class="name">parent</span>
<span class="name">style</span>: <span class="name">CircularGaugeStyle</span> {
<span class="name">id</span>: <span class="name">style</span>
<span class="keyword">function</span> <span class="name">degreesToRadians</span>(<span class="name">degrees</span>) {
<span class="keyword">return</span> <span class="name">degrees</span> <span class="operator">*</span> (<span class="name">Math</span>.<span class="name">PI</span> <span class="operator">/</span> <span class="number">180</span>);
}
<span class="name">background</span>: <span class="name">Canvas</span> {
<span class="name">onPaint</span>: {
var <span class="name">ctx</span> = <span class="name">getContext</span>(<span class="string">"2d"</span>);
<span class="name">ctx</span>.<span class="name">reset</span>();
<span class="name">ctx</span>.<span class="name">beginPath</span>();
<span class="name">ctx</span>.<span class="name">strokeStyle</span> <span class="operator">=</span> <span class="string">"#e34c22"</span>;
<span class="name">ctx</span>.<span class="name">lineWidth</span> <span class="operator">=</span> <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.02</span>;
<span class="name">ctx</span>.<span class="name">arc</span>(<span class="name">outerRadius</span>, <span class="name">outerRadius</span>, <span class="name">outerRadius</span> <span class="operator">-</span> <span class="name">ctx</span>.<span class="name">lineWidth</span> <span class="operator">/</span> <span class="number">2</span>,
<span class="name">degreesToRadians</span>(<span class="name">valueToAngle</span>(<span class="number">80</span>) <span class="operator">-</span> <span class="number">90</span>), <span class="name">degreesToRadians</span>(<span class="name">valueToAngle</span>(<span class="number">100</span>) <span class="operator">-</span> <span class="number">90</span>));
<span class="name">ctx</span>.<span class="name">stroke</span>();
}
}
<span class="name">tickmark</span>: <span class="name">Rectangle</span> {
<span class="name">visible</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator"><</span> <span class="number">80</span> <span class="operator">||</span> <span class="name">styleData</span>.<span class="name">value</span> <span class="operator">%</span> <span class="number">10</span> <span class="operator">==</span> <span class="number">0</span>
<span class="name">implicitWidth</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.02</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
<span class="name">implicitHeight</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.06</span>
<span class="name">color</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator">>=</span> <span class="number">80</span> ? <span class="string">"#e34c22"</span> : <span class="string">"#e5e5e5"</span>
}
<span class="name">minorTickmark</span>: <span class="name">Rectangle</span> {
<span class="name">visible</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator"><</span> <span class="number">80</span>
<span class="name">implicitWidth</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.01</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
<span class="name">implicitHeight</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.03</span>
<span class="name">color</span>: <span class="string">"#e5e5e5"</span>
}
<span class="name">tickmarkLabel</span>: <span class="name">Text</span> {
<span class="name">font</span>.pixelSize: <span class="name">Math</span>.<span class="name">max</span>(<span class="number">6</span>, <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.1</span>)
<span class="name">text</span>: <span class="name">styleData</span>.<span class="name">value</span>
<span class="name">color</span>: <span class="name">styleData</span>.<span class="name">value</span> <span class="operator">>=</span> <span class="number">80</span> ? <span class="string">"#e34c22"</span> : <span class="string">"#e5e5e5"</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
}
<span class="name">needle</span>: <span class="name">Rectangle</span> {
<span class="name">y</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.15</span>
<span class="name">implicitWidth</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.03</span>
<span class="name">implicitHeight</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.9</span>
<span class="name">antialiasing</span>: <span class="number">true</span>
<span class="name">color</span>: <span class="string">"#e5e5e5"</span>
}
<span class="name">foreground</span>: <span class="name">Item</span> {
<span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
<span class="name">width</span>: <span class="name">outerRadius</span> <span class="operator">*</span> <span class="number">0.2</span>
<span class="name">height</span>: <span class="name">width</span>
<span class="name">radius</span>: <span class="name">width</span> <span class="operator">/</span> <span class="number">2</span>
<span class="name">color</span>: <span class="string">"#e5e5e5"</span>
<span class="name">anchors</span>.centerIn: <span class="name">parent</span>
}
}
}
}
}</pre>
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