swt：如何仅更新（重绘）canvas 的一部分

Question

我正尝试在 SWT 中更新 canvas 的一部分，但我不知道该怎么做。

我读到我必须使用 setClipping，文档确实说： "Sets the area of the receiver which can be changed by drawing operations to the rectangular area specified by the argument. Specifying null for the rectangle reverts the receiver's clipping area to its original value."

所以我刚刚尝试过但没有成功，这里有一个简单的例子：

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;


public class SimpleCanvas {

    boolean manualDraw=false;
    public void run() {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setText("Canvas Example");
        createContents(shell);
        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }
        display.dispose();
    }

    /**
     * Creates the main window's contents
     * 
     * @param shell the main window
     */
    private void createContents(Shell shell) {
        shell.setLayout(new FillLayout());

        // Create a canvas
        Canvas canvas = new Canvas(shell, SWT.NONE);

        // Create a button on the canvas
        Button button = new Button(shell, SWT.PUSH);
        button.setBounds(10, 10, 300, 40);
        button.setText("TEST");
        button.addListener(SWT.Selection, new Listener() {
            public void handleEvent(Event e) {
                switch (e.type) {
                case SWT.Selection:
                    manualDraw=true;
                    canvas.redraw();
                    break;
                }
            }
        });

        // Create a paint handler for the canvas
        canvas.addPaintListener(new PaintListener() {
            public void paintControl(PaintEvent e) {

                if (manualDraw){
                    e.gc.setForeground(e.display.getSystemColor(SWT.COLOR_GREEN));
                    e.gc.setClipping(90,90,60,60);
                    e.gc.drawRectangle(90,90,30,30);
                    return ;
                }


                Rectangle rect = ((Canvas) e.widget).getBounds();
                e.gc.setForeground(e.display.getSystemColor(SWT.COLOR_RED));
                e.gc.drawText("DRAW TEXT", 0, 0);
                e.gc.dispose();
            }
        });
    }

    /**
     * The application entry point
     * 
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new SimpleCanvas().run();
    }
}

你能帮我理解我做错了什么吗？

提前致谢。

Answer 1

我发现了问题。为了只更新 canvas 的一部分，我不必调用 :

canvas.redraw();

并在那里绘制 canvas 的一部分，而是从 canvas 获取 GC 并在那里使用 setClipping，因此调用类似的东西：

public void redrawCanvas (Canvas canvas) {
        GC gc = new GC(canvas);
        gc.setClipping(90,90,60,60);
        gc.drawRectangle(90,90,30,30);
        gc.dispose();
    }

swt：如何仅更新（重绘）canvas 的一部分

swt: How to update(redraw) only a portion of a canvas

java

swt