title: Android - How to draw an arc based gradient
body: <p>I am trying to create an arc (variable number of degrees) that gradually goes from one color to another. From example from blue to red:<br><br>
  <img src="https://i.stack.imgur.com/ozRJN.jpg" alt="enter image description here"></p>
  
  <p>This is my code:</p>
  
  <pre><code>SweepGradient shader = new SweepGradient(center.x, center.y, resources.getColor(R.color.startColor),resources.getColor(R.color.endColor));
  Paint paint = new Paint()
  paint.setStrokeWidth(1);
  paint.setStrokeCap(Paint.Cap.FILL);
  paint.setStyle(Paint.Style.FILL);
  paint.setShader(shader);
  canvas.drawArc(rectF, startAngle, sweepAngle, true, paint);
  </code></pre>
  
  <p>But the result is the entire arc is painted with the same color.</p>
  
  <p><strong>Edit:</strong><br>
  After more experimenting, I found out that the color spread is determined by the angle of the arc. If I draw an arc with a small angle, only the first color is displayed. The larger the angle, more colors are drawn. If the angle is small it seems that there is no gradient. <br>Here is an example. I am drawing 4 arcs - 90, 180, 270 and 360:</p>
  
  <pre><code>RectF rect1 = new RectF(50, 50, 150, 150);
  Paint paint1 = new Paint();
  paint1.setStrokeWidth(1);
  paint1.setStrokeCap(Paint.Cap.SQUARE);
  paint1.setStyle(Paint.Style.FILL);
  
  SweepGradient gradient1 = new SweepGradient(100, 100,
          Color.RED, Color.BLUE);
  paint1.setShader(gradient1);
  
  canvas.drawArc(rect1, 0, 90, true, paint1);
  
  RectF rect2 = new RectF(200, 50, 300, 150);
  Paint paint2 = new Paint();
  paint2.setStrokeWidth(1);
  paint2.setStrokeCap(Paint.Cap.SQUARE);
  paint2.setStyle(Paint.Style.FILL);
  
  SweepGradient gradient2 = new SweepGradient(250, 100,
          Color.RED, Color.BLUE);
  paint2.setShader(gradient2);
  
  canvas.drawArc(rect2, 0, 180, true, paint2);
  
  RectF rect3 = new RectF(50, 200, 150, 300);
  Paint paint3 = new Paint();
  paint3.setStrokeWidth(1);
  paint3.setStrokeCap(Paint.Cap.SQUARE);
  paint3.setStyle(Paint.Style.FILL);
  
  SweepGradient gradient3 = new SweepGradient(100, 250,
          Color.RED, Color.BLUE);
  paint3.setShader(gradient3);
  
  canvas.drawArc(rect3, 0, 270, true, paint3);
  
  RectF rect4 = new RectF(200, 200, 300, 300);
  Paint paint4 = new Paint();
  paint4.setStrokeWidth(1);
  paint4.setStrokeCap(Paint.Cap.SQUARE);
  paint4.setStyle(Paint.Style.FILL);
  
  SweepGradient gradient4 = new SweepGradient(250, 250,
          Color.RED, Color.BLUE);
  paint4.setShader(gradient4);
  
  canvas.drawArc(rect4, 0, 360, true, paint4);
  </code></pre>
  
  <p>And here is the result:</p>
  
  <p><img src="https://i.stack.imgur.com/4VsFW.png" alt="enter image description here"></p>
  
  <p>This is surprising because I'd expect the RED to be at the start of the arc, the BLUE at the end and enything between to be spread evenly regardless of angle. <br>
  I tried to space the colors manually using the positions parameter but the results were the same:</p>
  
  <pre><code>int[] colors = {Color.RED, Color.BLUE};
  float[] positions = {0,1};
  SweepGradient gradient = new SweepGradient(100, 100, colors , positions);
  </code></pre>
  
  <p>Any idea how to solve this?</p>