intro/brush.html


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      Brushes | GoJS
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      <div class="px-4 pb-16 w-full overflow-hidden prose">
        
<h1>GoJS Brushes</h1>
<p>
  A <a>Brush</a> holds color information and describes how to draw the inside of a Shape or the stroke of a shape or a TextBlock or the background of any
  GraphObject.
</p>

<p>
  A Brush must not be modified once it has been assigned to a GraphObject, such as the <a>Shape.fill</a> or <a>TextBlock.stroke</a> or
  <a>GraphObject.background</a>. However, a Brush may be shared by multiple GraphObjects.
</p>

<h2 id="SolidBrushes">Solid Brushes</h2>

The simplest brushes are defined by a single solid color. Because they are so simple, anywhere you want a single-color brush you can substitute a valid CSS
color string.

<pre class="lang-js" id="simpleBrushes"><code>
  diagram.add(
    new go.Part()
      .add(
        new go.Shape("Circle", {
            fill: new go.Brush({ color: "palegreen" })
          })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape("Circle", {
            fill: "palegreen"
          })
      ));
</code></pre>
<script>
  goCode('simpleBrushes', 600, 120);
</script>

<p>Many CSS color strings are valid, including named colors, hex values, RGB values, and RGBA values.</p>

<pre class="lang-js" id="simpleBrushes2"><code>
  diagram.layout = new go.GridLayout();

  diagram.add(
    new go.Part()
      .add(
        new go.Shape("Circle", {
          fill: "#DFAD83"
        })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape("Circle", {
          fill: "rgba(0,255,0,.3)" // semi transparent green
        })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape("Circle", {
            fill: "rgba(0,255,0,.3)",
            stroke: '#DFBB00',
            strokeWidth: 4,
            background: 'coral'
          })
      ));
</code></pre>
<script>
  goCode('simpleBrushes2', 600, 120);
</script>

<h2 id="GradientBrushes">Gradient Brushes</h2>

<p>Gradient brushes are defined by setting the type and adding a number of color stops to the Brush.</p>
<pre class="lang-js"><code>
  // constructs a Linear gradient brush
  const brush = new go.Brush(go.BrushType.Linear);
  brush.addColorStop(0, "blue");
  brush.addColorStop(1, "red");
</code></pre>

<p>To simplify the syntax, you can use the constructor's initialization argument:</p>
<pre class="lang-js"><code>
  // constructs the same Brush
  const brush = new go.Brush("Linear", { 0.0: "blue", 1.0: "red" });
</code></pre>

<p>Some examples follow:</p>

<pre class="lang-js" id="gradients1"><code>
  diagram.add(
    new go.Part("Table")
      .add(
        new go.Shape({ row: 0, column: 0,
            figure: "Circle", width: 100, height: 100, margin: 5,
            // A linear gradient brush from blue to red, going from top to bottom (default)
            fill: new go.Brush("Linear", { 0.0: "blue", 1.0: "red" })
          }),
        new go.Shape({ row: 0, column: 1,
            figure: "Circle", width: 100, height: 100, margin: 5,
            // A linear gradient brush from blue to red, going from bottom to top
            // by defining start and end spots
            fill: new go.Brush("Linear", { 0.0: "blue", 1.0: "red", start: go.Spot.Bottom, end: go.Spot.Top })
          })
    ));
</code></pre>
<script>
  goCode('gradients1', 600, 120);
</script>

<p>Brushes can have any number of color stops:</p>

<pre class="lang-js" id="gradients2"><code>
  diagram.add(
    new go.Part("Table")
      .add(
        new go.Shape({ row: 0, column: 0,
            figure: "Rectangle", width: 100, height: 100, margin: 5,
            // A rainbow linear gradient brush:
            fill: new go.Brush("Linear", {
              0.0: "rgba(255, 0, 0, 1)",
              0.15: "rgba(255, 255, 0, 1)",
              0.30: "rgba(0, 255, 0, 1)",
              0.50: "rgba(0, 255, 255, 1)",
              0.65: "rgba(0, 0, 255, 1)",
              0.80: "rgba(255, 0, 255, 1)",
              1: "rgba(255, 0, 0, 1)"
            })
          }),
        new go.Shape({ row: 0, column: 1,
            figure: "Rectangle", width: 100, height: 100, margin: 5,
            // A rainbow radial gradient brush:
            fill: new go.Brush("Radial", {
              0.0: "rgba(255, 0, 0, 1)",
              0.15: "rgba(255, 255, 0, 1)",
              0.30: "rgba(0, 255, 0, 1)",
              0.50: "rgba(0, 255, 255, 1)",
              0.65: "rgba(0, 0, 255, 1)",
              0.80: "rgba(255, 0, 255, 1)",
              1: "rgba(255, 0, 0, 1)"
            })
          })
      ));
</code></pre>
<script>
  goCode('gradients2', 600, 120);
</script>

<p>
  Radial gradient brushes can be controlled with <a>Brush.startRadius</a> and <a>Brush.endRadius</a>, which default to zero and NaN, respectively, meaning the
  gradient begins at the very center and goes to the farthest measured edge of the object.
</p>

<pre class="lang-js" id="gradients21"><code>
  diagram.layout = new go.GridLayout();

  diagram.add(
    new go.Part()
      .add(
        new go.Shape({
            figure: "Rectangle", width: 100, height: 100, margin: 5,
            // A rainbow radial gradient brush:
            fill: new go.Brush("Radial", {
              0.0: "red", 1: "black"
            })
          })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape({
            figure: "Rectangle", width: 100, height: 100, margin: 5,
            // A rainbow radial gradient brush:
            fill: new go.Brush("Radial", {
              startRadius: 30, 0.0: "red", 1: "black"
            })
          })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape({
            figure: "Rectangle", width: 100, height: 100, margin: 5,
            // A rainbow radial gradient brush:
            fill: new go.Brush("Radial", {
              startRadius: 30, endRadius: 40, 0.0: "red", 1: "black"
            })
          })
      ));
</code></pre>
<script>
  goCode('gradients21', 600, 120);
</script>

<p>Several GraphObjects can share the same Brush:</p>

<pre class="lang-js" id="gradients3"><code>

  diagram.layout = new go.GridLayout();

  // Create one brush for several GraphObjects to share:
  const rainbow = new go.Brush("Linear", {
                        0.0: "rgba(255, 0, 0, 1)",
                        0.15: "rgba(255, 255, 0, 1)",
                        0.30: "rgba(0, 255, 0, 1)",
                        0.50: "rgba(0, 255, 255, 1)",
                        0.65: "rgba(0, 0, 255, 1)",
                        0.80: "rgba(255, 0, 255, 1)",
                        1: "rgba(255, 0, 0, 1)"
                      });
  diagram.add(
    new go.Part()
      .add(
        new go.Shape({ figure: "Rectangle", width: 100, height: 100, fill: rainbow })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape({ figure: "Fragile", width: 50, height: 50, angle: 45, fill: rainbow })
      ));

  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape({ figure: "Rectangle", fill: rainbow }),
        new go.TextBlock("text", { font: 'bold 32pt sans-serif', stroke: rainbow, angle: 90 })
      ));

  diagram.add(
    new go.Part()
      .add(
        new go.Shape({ figure: "Circle", width: 70, height: 70, angle: 180,
                      fill: null, strokeWidth: 10, stroke: rainbow })
      ));
</code></pre>

<script>
  goCode('gradients3', 600, 120);
</script>

<h2 id="PatternBrushes">Pattern Brushes</h2>
<p>The following example sets up two Pattern brushes, one using an HTML Canvas with content drawn to it, which looks like this:</p>
<div id="patternCanvas"></div>
<script type="text/javascript">
  // set up an 40x40 HTML Canvas and draw on it to create a repeating "tile" to use as a pattern
  const patternCanvas = document.createElement('canvas');
  patternCanvas.width = 40;
  patternCanvas.height = 40;
  const pctx = patternCanvas.getContext('2d');

  // This creates a shape similar to a diamond leaf
  pctx.beginPath();
  pctx.moveTo(0.0, 40.0);
  pctx.lineTo(26.9, 36.0);
  pctx.bezierCurveTo(31.7, 36.0, 36.0, 32.1, 36.0, 27.3);
  pctx.lineTo(40.0, 0.0);
  pctx.lineTo(11.8, 3.0);
  pctx.bezierCurveTo(7.0, 3.0, 3.0, 6.9, 3.0, 11.7);
  pctx.lineTo(0.0, 40.0);
  pctx.closePath();
  pctx.fillStyle = 'rgb(188, 222, 178)';
  pctx.fill();
  pctx.lineWidth = 0.8;
  pctx.strokeStyle = 'rgb(0, 156, 86)';
  pctx.lineJoin = 'miter';
  pctx.miterLimit = 4.0;
  pctx.stroke();

  document.getElementById('patternCanvas').appendChild(patternCanvas);
</script>

<p>The other Pattern Brush uses this image:</p>
<p><img src="images/pattern.jpg" /></p>

<pre class="lang-js" id="diagramPre"><code>
  // set up an 40x40 HTML Canvas and draw on it to create a repeating "tile" to use as a pattern
  function makePattern() {
    const patternCanvas = document.createElement('canvas');
    patternCanvas.width = 40;
    patternCanvas.height = 40;
    const pctx = patternCanvas.getContext('2d');

    // This creates a shape similar to a diamond leaf
    pctx.beginPath();
    pctx.moveTo(0.0, 40.0);
    pctx.lineTo(26.9, 36.0);
    pctx.bezierCurveTo(31.7, 36.0, 36.0, 32.1, 36.0, 27.3);
    pctx.lineTo(40.0, 0.0);
    pctx.lineTo(11.8, 3.0);
    pctx.bezierCurveTo(7.0, 3.0, 3.0, 6.9, 3.0, 11.7);
    pctx.lineTo(0.0, 40.0);
    pctx.closePath();
    pctx.fillStyle = "rgb(188, 222, 178)";
    pctx.fill();
    pctx.lineWidth = 0.8;
    pctx.strokeStyle = "rgb(0, 156, 86)";
    pctx.lineJoin = "miter";
    pctx.miterLimit = 4.0;
    pctx.stroke();

    return patternCanvas;
  }


  diagram.nodeTemplate =
    new go.Node("Spot", { resizable: true, resizeObjectName: 'SHAPE' })
      .add(
        new go.Shape("Rectangle", { name: 'SHAPE', strokeWidth: 0, stroke: null })
          .bind("fill"),
        new go.TextBlock({ margin: 10, font: "bold 18px Verdana" })
          .bind("text")
      );

  const img = new Image();
  img.src = 'images/pattern.jpg';

  // Use an image as a pattern
  const patternBrush = new go.Brush("Pattern", { pattern: img });
  // use a reference to an HTML Canvas (with renderings on it) as a pattern:
  const patternBrush2 = new go.Brush("Pattern", { pattern: makePattern() });


  diagram.model = new go.GraphLinksModel(
    [
      { key: 1, text: "Alpha", fill: patternBrush },
      { key: 2, text: "Beta",  fill: patternBrush2 }
    ]);
</code></pre>
<div style="width: 100%">
  <span id="diagramSpan" style="display: inline-block; vertical-align: top">
    <p><b>The result:</b></p>
  </span>
</div>
<script>
  goCode('diagramPre', 500, 300, 'diagramSpan');
</script>

<h2 id="BrushFunctions">Brush Functions</h2>
<p>There are some functions available for generating different colors or modifying Brush colors:</p>
<ul>
  <li><a>Brush.randomColor</a> - returns a random hexadecimal color value</li>

  <li><a>Brush.lightenBy</a> and <a>Brush.darkenBy</a> - return lightened or darkened colors/brushes; there are both instance methods and static functions</li>
  <li><a>Brush.lighten</a> and <a>Brush.darken</a> - convenience static functions which return lightened or darkened colors</li>
  <li><a>Brush.mix</a> - mixes two colors together</li>
  <li><a>Brush.isDark</a> - determines whether a color is dark, often used in bindings; there are both instance methods and static functions</li>
</ul>
<p>In the following example, parts use the lighten and darken functions to get suitable colors for their stroke/fill.</p>
<pre class="lang-js" id="functions"><code>
  diagram.layout = new go.GridLayout();
  const color1 = "rgb(80, 130, 210)";
  const color2 = go.Brush.randomColor(192, 224);
  const gradBrush = new go.Brush("Linear", { 0: color1, 1: color2 });
  function shapeStyle() {
    return { figure: "Ellipse", width: 120, height: 80, strokeWidth: 4 };
  }

  // static Brush methods
  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: color1, stroke: go.Brush.darken(color1)
        }),
        new go.TextBlock("dark stroke")
      ));

  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: color1, stroke: go.Brush.darkenBy(color1, .4)
        }),
        new go.TextBlock("darker stroke")
      ));

  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: go.Brush.lighten(color1), stroke: color1
        }),
        new go.TextBlock("light fill")
      ));

  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: go.Brush.lightenBy(color1, .4), stroke: color1
        }),
        new go.TextBlock("lighter fill")
      ));

  // instance Brush methods
  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: gradBrush.copy().lightenBy(.2)
        }),
        new go.TextBlock("lighter")
      ));

  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: gradBrush
        }),
        new go.TextBlock("normal")
      ));

  diagram.add(
    new go.Part("Auto")
      .add(
        new go.Shape(shapeStyle(), {
          fill: gradBrush.copy().darkenBy(.2)
        }),
        new go.TextBlock("darker")
      ));
</code></pre>
<script>
  goCode('functions', 600, 200);
</script>
<p>In the following example, the color of text is determined by whether the background shape is dark.</p>
<pre class="lang-js" id="functions2"><code>
  diagram.layout = new go.GridLayout();

  diagram.nodeTemplate =
    new go.Node("Auto", { desiredSize: new go.Size(80, 40) })
      .add(
        new go.Shape("RoundedRectangle", { strokeWidth: 0 })
          .bind("fill", "color"),
        new go.TextBlock({ margin: 8 })
          .bind("stroke", "color",
                // dark nodes use white text, light nodes use dark text
                c => go.Brush.isDark(c) ? "white" : "black")
          .bind("text")
      );

  diagram.model = new go.Model(
    [
      { text: "Alpha", color: "white" },
      { text: "Beta", color: "black" },
      { text: "Gamma", color: "darkblue" },
      { text: "Delta", color: "lightblue" },
      { text: "Epsilon", color: "darkgreen" },
      { text: "Zeta", color: "lightgreen" },
      { text: "Eta", color: "darkred" },
      { text: "Theta", color: "lightcoral" }
    ]
  )
</code></pre>
<script>
  goCode('functions2', 600, 200);
</script>

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