在javafx Canvas/GraphicsContext中用透明颜色覆盖路径

Question

null

http://docs.oracle.com/javase/8/javafx/api/javafx/scene/canvas/graphicscontext.html

对第一条注释的补充：我不是使用路径节点，而是使用画布节点使用GraphicsContext执行呈现，因此不可能修改先前呈现的路径的颜色。我试着做一些事情

Canvas canvas = …;
final GraphicsContext context = canvas.getGraphicsContext();
context.setFill(Color.BLUE);
context.fillRect(0,0,100,100);
…
…

稍后我想重置路径中的像素到透明

context.setStroke(Color.TRANSPARENT);
context.beginPath();
context.moveTo(0, 0);
context.lineTo(10,10);
…
context.stroke();

然而，当混合被应用时，这不起作用。在其他呈现库中，可以使用例如上面提到的混合/合成方法之一来实现这一点，但直到现在，我还无法在JavaFX中识别出这样的功能。

Answer 1

我还没有找到一种机制来根据路径清除画布。但以下是手动操作的方法：

• 创建在其上绘制路径的掩码
• 手动混合图像和掩码

应用了带有路径的掩码的蓝色矩形的示例：

public class ManualBlendWithMask extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {

        Group root = new Group();

        // create canvas
        Canvas canvas = new Canvas(200, 200);
        canvas.setTranslateX(100);
        canvas.setTranslateY(100);

        // create canvas with blue rectangle
        GraphicsContext canvasGC = canvas.getGraphicsContext2D();
        canvasGC.setFill(Color.BLUE);
        canvasGC.fillRect(0, 0, canvas.getWidth(), canvas.getHeight());

        // create mask
        Canvas mask = new Canvas( canvas.getWidth(), canvas.getHeight());
        GraphicsContext maskGC = mask.getGraphicsContext2D();
        maskGC.setFill(Color.WHITE);
        maskGC.fillRect(0, 0, mask.getWidth(), mask.getHeight());

        // draw path
        maskGC.setStroke(Color.BLACK);
        maskGC.setLineWidth(20);
        maskGC.beginPath();
        maskGC.moveTo(0, 0);
        maskGC.lineTo(400, 400);
        maskGC.stroke();

        // get image from canvas
        WritableImage srcImage = new WritableImage((int) canvas.getWidth(), (int) canvas.getHeight());
        srcImage = canvas.snapshot(null, srcImage);

        // get image from mask
        WritableImage srcMask = new WritableImage((int) mask.getWidth(), (int) mask.getHeight());
        srcMask = mask.snapshot(null, srcMask);

        PixelReader maskReader = srcMask.getPixelReader();
        PixelReader imageReader = srcImage.getPixelReader();

        int width = (int) srcMask.getWidth();
        int height = (int) srcMask.getHeight();

        // create dest image
        WritableImage dest = new WritableImage(width, height);
        PixelWriter writer = dest.getPixelWriter();

        // blend image and mask
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {

                Color maskColor = maskReader.getColor(x, y);
                Color imageColor = imageReader.getColor(x, y);

                if (maskColor.equals(Color.WHITE)) {
                    writer.setColor(x, y, imageColor);
                }

            }
        }

        // clear canvas and fill it with the blended image
        canvasGC = canvas.getGraphicsContext2D();
        canvasGC.clearRect(0, 0, canvas.getWidth(), canvas.getHeight());
        canvasGC.drawImage(dest, 0, 0);

        // draw background with gradient
        Rectangle rect = new Rectangle(400, 400);
        rect.setFill(new LinearGradient(0, 0, 1, 1, true, CycleMethod.REFLECT, new Stop(0, Color.RED), new Stop(1, Color.YELLOW)));

        // show nodes
        root.getChildren().addAll(rect, canvas);

        primaryStage.setScene(new Scene(root, 400, 400));
        primaryStage.show();

    }

}