如何在 JavaFX Canvas 上绘制旋转的图像？答案

【问题标题】：How to draw image rotated on JavaFX Canvas?如何在 JavaFX Canvas 上绘制旋转的图像？
【发布时间】：2013-08-18 02:22:35
【问题描述】：

我想在旋转的画布上绘制图像。使用drawImage(image, 0, 0) 我可以绘制图像，但我如何将该图像旋转 45 度并绘制它，然后在同一画布上绘制另一个旋转 -50 度的图像？

graphicContext2D 对我不起作用，因为它会旋转所有画布内容。

【问题讨论】：

标签： javafx-2 javafx-8

【解决方案1】：

嗯，我从来没有使用过 JavaFX，但是浏览它的 API 文档，我想出了这个解决方案（我还没有真正尝试过，所以它可能是错误的）：

Canvas canvas = ...
Image img = ...
GraphicsContext gc = canvas.getGraphicsContext2D();

gc.save(); // saves the current state on stack, including the current transform
gc.rotate(45);
gc.drawImage(img);
gc.restore(); // back to original state (before rotation)

gc.save();
gc.rotate(-50);
gc.drawImage(img);
gc.restore();

我不知道它是否在这里工作，但这个想法（转换堆栈）是从其他绘图 API（如 OpenGL）借来的。

【讨论】：

【解决方案2】：

这是一个示例，遵循与 Katona 的答案类似的原则，唯一的区别是它通过应用自定义变换来围绕任意枢轴点旋转图像。

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.canvas.*;
import javafx.scene.image.Image;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.transform.Rotate;
import javafx.stage.Stage;

/** Rotates images round pivot points and places them in a canvas */
public class RotatedImageInCanvas extends Application {
    /**
     * Sets the transform for the GraphicsContext to rotate around a pivot point.
     *
     * @param gc the graphics context the transform to applied to.
     * @param angle the angle of rotation.
     * @param px the x pivot co-ordinate for the rotation (in canvas co-ordinates).
     * @param py the y pivot co-ordinate for the rotation (in canvas co-ordinates).
     */
    private void rotate(GraphicsContext gc, double angle, double px, double py) {
        Rotate r = new Rotate(angle, px, py);
        gc.setTransform(r.getMxx(), r.getMyx(), r.getMxy(), r.getMyy(), r.getTx(), r.getTy());
    }

    /**
     * Draws an image on a graphics context.
     *
     * The image is drawn at (tlpx, tlpy) rotated by angle pivoted around the point:
     *   (tlpx + image.getWidth() / 2, tlpy + image.getHeight() / 2)
     *
     * @param gc the graphics context the image is to be drawn on.
     * @param angle the angle of rotation.
     * @param tlpx the top left x co-ordinate where the image will be plotted (in canvas co-ordinates).
     * @param tlpy the top left y co-ordinate where the image will be plotted (in canvas co-ordinates).
     */
    private void drawRotatedImage(GraphicsContext gc, Image image, double angle, double tlpx, double tlpy) {
        gc.save(); // saves the current state on stack, including the current transform
        rotate(gc, angle, tlpx + image.getWidth() / 2, tlpy + image.getHeight() / 2);
        gc.drawImage(image, tlpx, tlpy);
        gc.restore(); // back to original state (before rotation)
    }

    @Override public void start(Stage stage) {
        Image image = new Image(
            "http://worldpress.org/images/maps/world_600w.jpg", 350, 0, true, true
        );

        // creates a canvas on which rotated images are rendered.
        Canvas canvas = new Canvas(600, 400);
        GraphicsContext gc = canvas.getGraphicsContext2D();

        drawRotatedImage(gc, image,  40,   0,   0);
        drawRotatedImage(gc, image, -50, 400, 200);

        // supplies a tiled background image on which the canvas is drawn.
        StackPane stack = new StackPane();
        stack.setMaxSize(canvas.getWidth(), canvas.getHeight());
        stack.setStyle("-fx-background-image: url('http://1.bp.blogspot.com/_wV5JMD1OISg/TDYTYxuxR4I/AAAAAAAAvSo/a0zT8nwPV8U/s400/louis-vuitton-nice-beautiful.jpg');");
        stack.getChildren().add(
                canvas
        );

        // places a resizable padded frame around the canvas.
        StackPane frame = new StackPane();
        frame.setPadding(new Insets(20));
        frame.getChildren().add(stack);

        stage.setScene(new Scene(frame, Color.BURLYWOOD));
        stage.show();
    }

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

【讨论】：

这个解决方案更适合我的情况。

【解决方案3】：

上述问题也可以通过创建不同的画布层来解决。

private void createLayers(){
        // Layers 1&2 are the same size
        layer1 = new Canvas(300,250);
        layer2 = new Canvas(300,250);

        // Obtain Graphics Contexts
        gc1 = layer1.getGraphicsContext2D();
        gc1.setFill(Color.GREEN);
        gc1.fillOval(50,50,20,20);
        gc1.getCanvas().setRotate(45);
        gc2 = layer2.getGraphicsContext2D();
        gc2.setFill(Color.BLUE);
        gc2.fillOval(100,100,20,20);
        gc.getCanvas().setRotate(135);
    }
        ...

 private void addLayers(){
        // Add Layers
        borderPane.setTop(cb);        
        Pane pane = new Pane();
        pane.getChildren().add(layer1);
        pane.getChildren().add(layer2);
        layer1.toFront();
        borderPane.setCenter(pane);    
        root.getChildren().add(borderPane);
    }

【讨论】：

【解决方案4】：

我在使用 ImageViews 时遇到了类似的问题，在旋转和缩放图像后，父容器的布局管理器没有正确调整它的大小。

根据这里提出的想法，我创建了一个 ImageCanvas，它反映了渲染图像的尺寸，无论是旋转还是缩放。

见https://github.com/treimers/JfxImageCanvas

享受托尔斯滕

【讨论】：