GraphicsContext provides a set of methods to draw and fill geometric shapes. Typically, these methods need coordinates to be passed as their parameters, either directly or in a form of an array of double values. The coordinates are always relative to the Canvas, whose origin is at the top left corner.

Note: GraphicsContext will not draw outside of Canvas boundaries, i.e. trying to draw outside the Canvas area defined by its size and resizing it afterwards will yield no result.

The example below shows how to draw three semi-transparent filled geometric shapes outlined with a black stroke.

Canvas canvas = new Canvas(185, 70);
GraphicsContext gc = canvas.getGraphicsContext2D();

// Set stroke color, width, and global transparency
gc.setStroke(Color.BLACK);   
gc.setLineWidth(2d);
gc.setGlobalAlpha(0.5d);

// Draw a square
gc.setFill(Color.RED);
gc.fillRect(10, 10, 50, 50);
gc.strokeRect(10, 10, 50, 50);

// Draw a triangle
gc.setFill(Color.GREEN);
gc.fillPolygon(new double[]{70, 95, 120}, new double[]{60, 10, 60}, 3);
gc.strokePolygon(new double[]{70, 95, 120}, new double[]{60, 10, 60}, 3);

// Draw a circle
gc.setFill(Color.BLUE);
gc.fillOval(130, 10, 50, 50);
gc.strokeOval(130, 10, 50, 50);