Path construction and painting operators in Java

Generator QR Code JIS X 0510 in Java Path construction and painting operators

W W*

clip() eoClip()

Modifies the current clipping path by intersecting it with the current path, using the nonzero winding rule. Modifies the current clipping path by intersecting it with the current path, using the even-odd rule.

When you construct a path using the methods from table 14.2, you can stroke those paths. Stroking a path means you re going to draw the line segments of the subpaths. The color used by default is black, but you can change this color with one of the setColorStroke() methods in table 14.8. Filling a path means you re going to paint the entire region enclosed by the path. By default, shapes are filled using the nonzero winding number rule.

When I close my eyes, I can still see how our professor of analytic geometry filled two of his nine blackboards explaining how to determine whether or not a given point is inside a path. With the nonzero winding number rule, you need to draw a line from that point in any direction, and examine every intersection of the path with this line. Start with a count of zero; add one each time a subpath crosses the line from left to right; subtract one each time a subpath crosses from right to left. Do this until there are no more path segments to cross. If the result is zero, the point is outside the path; otherwise, it s inside. An alternative to the nonzero winding number rule is the even-odd rule. Again, you need to draw a line from the point that s being examined to infinity. Now count the number of path segments that are crossed, regardless of the direction. If this number is odd, the point is inside; if even, the point is outside. If you don t like to read definitions, have a look at the stars and circles in figure 14.2.

The paths of the star and circle shapes are constructed using listing 14.2. Observe that the star is composed of five straight lines, four of which are created using the lineTo() method and one implicitly using closePath().

public static void createStar(PdfContentByte canvas, float x, float y) { canvas.moveTo(x + 10, y); canvas.lineTo(x + 80, y + 60); canvas.lineTo(x, y + 60); canvas.lineTo(x + 70, y); canvas.lineTo(x + 40, y + 90); canvas.closePath(); } public static void createCircle(PdfContentByte canvas, float x, float y, float r, boolean clockwise) { float b = 0.5523f; if (clockwise) { canvas.moveTo(x + r, y); canvas.curveTo(x + r, y - r * b, x + r * b, y - r, x, y - r); canvas.curveTo(x - r * b, y - r, x - r, y - r * b, x - r, y); canvas.curveTo(x - r, y + r * b, x - r * b, y + r, x, y + r); canvas.curveTo(x + r * b, y + r, x + r, y + r * b, x + r, y); } else { canvas.moveTo(x + r, y); canvas.curveTo(x + r, y + r * b, x + r * b, y + r, x, y + r); canvas.curveTo(x - r * b, y + r, x - r, y + r * b, x - r, y); canvas.curveTo(x - r, y - r * b, x - r * b, y - r, x, y - r); canvas.curveTo(x + r * b, y - r, x + r, y - r * b, x + r, y); } }

The circle is constructed using four B zier curves. With the method createCircle(), you can construct the path clockwise and counterclockwise. Now look at the next listing to see how the shapes in figure 14.2 were added.

Listing 14.3 PathConstructionAndPainting.java (continued)

createStar(canvas, x, y); createCircle(canvas, x + radius, createCircle(canvas, x + radius, canvas.fill(); x += 2 * radius + gutter; createStar(canvas, x, y); createCircle(canvas, x + radius, createCircle(canvas, x + radius, canvas.eoFill(); x += 2 * radius + gutter; createStar(canvas, x, y); canvas.newPath(); createCircle(canvas, x + radius, createCircle(canvas, x + radius, x += 2 * radius + gutter; createStar(canvas, x, y); createCircle(canvas, x + radius, y - 70, radius, true); y - 70, radius / 2, true);