Android:如何在图像之上实现绘图

Question

目标是能够在拍摄的图像上书写/素描/绘制任何东西，并且在不破坏图像的情况下进行删除，使图像保持完整，并且在保存图像时，绘图和背景图像将是包含在最终输出中。

我构建了一个应用程序，它可以拍摄照片，然后将其发送到一个新的 Activity 进行预览和编辑，我应该能够在图像上绘制一个圆圈或一些线条。我能够通过创建位图并将其传递给新的 Canvas() 构造函数来做到这一点。

问题是我可以在图像上写字，但是当我使用删除模式时，图像也会被删除，我想实现一些让我删除而不破坏背景图像的东西，同时当我最终保存图像时，背景上的图像仍会包含在内。

我的 View 代码如下。

import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.MotionEvent;
import android.view.View;

public class DrawingView extends View {

    //drawing path
    private Path drawPath;
    //drawing and canvas paint
    private Paint drawPaint, canvasPaint;
    //initial color
    private int paintColor = 0xFF660000, paintAlpha = 255;
    //canvas
    private Canvas drawCanvas;
    //canvas bitmap
    private Bitmap canvasBitmap;
    //brush sizes
    private float brushSize, lastBrushSize;
    //erase flag
    private boolean erase=false;

    Bitmap bg;

    public DrawingView(Context context, AttributeSet attrs){
        super(context, attrs);
        setupDrawing();
    }

    //setup drawing
    private void setupDrawing(){

        //prepare for drawing and setup paint stroke properties
        brushSize = getResources().getInteger(R.integer.medium_size);
        lastBrushSize = brushSize;
        drawPath = new Path();
        drawPaint = new Paint();
        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(brushSize);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);
        canvasPaint = new Paint(Paint.DITHER_FLAG);

        Resources res = getResources();
        Bitmap bitmap = BitmapFactory.decodeResource(res, R.drawable.background);
        bg = bitmap.copy(Bitmap.Config.ARGB_8888, true);
    }

    //size assigned to view
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        drawCanvas = new Canvas(bg);
    }

    //draw the view - will be called after touch event
    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawBitmap(bg, 0, 0, canvasPaint);
        canvas.drawPath(drawPath, drawPaint);
    }

    //register user touches as drawing action
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float touchX = event.getX();
        float touchY = event.getY();
        //respond to down, move and up events
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                drawPath.moveTo(touchX, touchY);
                break;
            case MotionEvent.ACTION_MOVE:
                drawPath.lineTo(touchX, touchY);
                break;
            case MotionEvent.ACTION_UP:
                drawPath.lineTo(touchX, touchY);
                drawCanvas.drawPath(drawPath, drawPaint);
                drawPath.reset();
                break;
            default:
                return false;
        }
        //redraw
        invalidate();
        return true;

    }

    //update color
    public void setColor(String newColor){
        invalidate();
        //check whether color value or pattern name
        if(newColor.startsWith("#")){
            paintColor = Color.parseColor(newColor);
            drawPaint.setColor(paintColor);
            drawPaint.setShader(null);
        }
        else{
            //pattern
            int patternID = getResources().getIdentifier(
                    newColor, "drawable", "com.example.drawingfun");
            //decode
            Bitmap patternBMP = BitmapFactory.decodeResource(getResources(), patternID);
            //create shader
            BitmapShader patternBMPshader = new BitmapShader(patternBMP,
                    Shader.TileMode.REPEAT, Shader.TileMode.REPEAT);
            //color and shader
            drawPaint.setColor(0xFFFFFFFF);
            drawPaint.setShader(patternBMPshader);
        }
    }

    //set brush size
    public void setBrushSize(float newSize){
        float pixelAmount = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
                newSize, getResources().getDisplayMetrics());
        brushSize=pixelAmount;
        drawPaint.setStrokeWidth(brushSize);
    }

    //get and set last brush size
    public void setLastBrushSize(float lastSize){
        lastBrushSize=lastSize;
    }
    public float getLastBrushSize(){
        return lastBrushSize;
    }

    //set erase true or false
    public void setErase(boolean isErase){
        erase=isErase;
        drawPaint.setColor(Color.parseColor("#FFFFFF"));
        if(erase) drawPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        else drawPaint.setXfermode(null);
        drawPaint.setColor(paintColor);
    }

    //start new drawing
    public void startNew(){
        drawCanvas.drawColor(0, PorterDuff.Mode.CLEAR);
        invalidate();
    }

    //return current alpha
    public int getPaintAlpha(){
        return Math.round((float)paintAlpha/255*100);
    }

    //set alpha
    public void setPaintAlpha(int newAlpha){
        paintAlpha=Math.round((float)newAlpha/100*255);
        drawPaint.setColor(paintColor);
        drawPaint.setAlpha(paintAlpha);
    }
}

MainActivity.java是这个

import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
import android.widget.TextView;
import android.widget.Toast;

import java.util.UUID;


public class MainActivity extends Activity implements OnClickListener {

    //custom drawing view
    private DrawingView drawView;
    //buttons
    private ImageButton currPaint, drawBtn, eraseBtn, newBtn, saveBtn, opacityBtn;
    //sizes
    private float smallBrush, mediumBrush, largeBrush;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //get drawing view
        drawView = (DrawingView)findViewById(R.id.drawing);

//        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
//            drawView.setBackground(getResources().getDrawable(R.drawable.background, null));
//        }
//        else
//            drawView.setBackground(getResources().getDrawable(R.drawable.background));
        //get the palette and first color button
        LinearLayout paintLayout = (LinearLayout)findViewById(R.id.paint_colors);
        currPaint = (ImageButton)paintLayout.getChildAt(0);
        currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));

        //sizes from dimensions
        smallBrush = getResources().getInteger(R.integer.small_size);
        mediumBrush = getResources().getInteger(R.integer.medium_size);
        largeBrush = getResources().getInteger(R.integer.large_size);

        //draw button
        drawBtn = (ImageButton)findViewById(R.id.draw_btn);
        drawBtn.setOnClickListener(this);

        //set initial size
        drawView.setBrushSize(smallBrush);

        //erase button
        eraseBtn = (ImageButton)findViewById(R.id.erase_btn);
        eraseBtn.setOnClickListener(this);

        //new button
        newBtn = (ImageButton)findViewById(R.id.new_btn);
        newBtn.setOnClickListener(this);

        //save button
        saveBtn = (ImageButton)findViewById(R.id.save_btn);
        saveBtn.setOnClickListener(this);

        //opacity
        opacityBtn = (ImageButton)findViewById(R.id.opacity_btn);
        opacityBtn.setOnClickListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
//        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    //user clicked paint
    public void paintClicked(View view){
        //use chosen color

        //set erase false
        drawView.setErase(false);
        drawView.setPaintAlpha(100);
        drawView.setBrushSize(drawView.getLastBrushSize());

        if(view!=currPaint){
            ImageButton imgView = (ImageButton)view;
            String color = view.getTag().toString();
            drawView.setColor(color);
            //update ui
            imgView.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));
            currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint));
            currPaint=(ImageButton)view;
        }
    }

    @Override
    public void onClick(View view){

        if(view.getId()==R.id.draw_btn){
            //draw button clicked
            final Dialog brushDialog = new Dialog(this);
            brushDialog.setTitle("Brush size:");
            brushDialog.setContentView(R.layout.brush_chooser);
            //listen for clicks on size buttons
            ImageButton smallBtn = (ImageButton)brushDialog.findViewById(R.id.small_brush);
            smallBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setErase(false);
                    drawView.setBrushSize(smallBrush);
                    drawView.setLastBrushSize(smallBrush);
                    brushDialog.dismiss();
                }
            });
            ImageButton mediumBtn = (ImageButton)brushDialog.findViewById(R.id.medium_brush);
            mediumBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setErase(false);
                    drawView.setBrushSize(mediumBrush);
                    drawView.setLastBrushSize(mediumBrush);
                    brushDialog.dismiss();
                }
            });
            ImageButton largeBtn = (ImageButton)brushDialog.findViewById(R.id.large_brush);
            largeBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setErase(false);
                    drawView.setBrushSize(largeBrush);
                    drawView.setLastBrushSize(largeBrush);
                    brushDialog.dismiss();
                }
            });
            //show and wait for user interaction
            brushDialog.show();
        }
        else if(view.getId()==R.id.erase_btn){
            //switch to erase - choose size
            final Dialog brushDialog = new Dialog(this);
            brushDialog.setTitle("Eraser size:");
            brushDialog.setContentView(R.layout.brush_chooser);
            //size buttons
            ImageButton smallBtn = (ImageButton)brushDialog.findViewById(R.id.small_brush);
            smallBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setErase(true);
                    drawView.setBrushSize(smallBrush);
                    brushDialog.dismiss();
                }
            });
            ImageButton mediumBtn = (ImageButton)brushDialog.findViewById(R.id.medium_brush);
            mediumBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setErase(true);
                    drawView.setBrushSize(mediumBrush);
                    brushDialog.dismiss();
                }
            });
            ImageButton largeBtn = (ImageButton)brushDialog.findViewById(R.id.large_brush);
            largeBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setErase(true);
                    drawView.setBrushSize(largeBrush);
                    brushDialog.dismiss();
                }
            });
            brushDialog.show();
        }
        else if(view.getId()==R.id.new_btn){
            //new button
            AlertDialog.Builder newDialog = new AlertDialog.Builder(this);
            newDialog.setTitle("New drawing");
            newDialog.setMessage("Start new drawing (you will lose the current drawing)?");
            newDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener(){
                public void onClick(DialogInterface dialog, int which){
                    drawView.startNew();
                    dialog.dismiss();
                }
            });
            newDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener(){
                public void onClick(DialogInterface dialog, int which){
                    dialog.cancel();
                }
            });
            newDialog.show();
        }
        else if(view.getId()==R.id.save_btn){
            //save drawing
            AlertDialog.Builder saveDialog = new AlertDialog.Builder(this);
            saveDialog.setTitle("Save drawing");
            saveDialog.setMessage("Save drawing to device Gallery?");
            saveDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener(){
                public void onClick(DialogInterface dialog, int which){
                    //save drawing
                    drawView.setDrawingCacheEnabled(true);
                    //attempt to save
                    String imgSaved = MediaStore.Images.Media.insertImage(
                            getContentResolver(), drawView.getDrawingCache(),
                            UUID.randomUUID().toString()+".png", "drawing");
                    //feedback
                    if(imgSaved!=null){
                        Toast savedToast = Toast.makeText(getApplicationContext(),
                                "Drawing saved to Gallery!", Toast.LENGTH_SHORT);
                        savedToast.show();
                    }
                    else{
                        Toast unsavedToast = Toast.makeText(getApplicationContext(),
                                "Oops! Image could not be saved.", Toast.LENGTH_SHORT);
                        unsavedToast.show();
                    }
                    drawView.destroyDrawingCache();
                }
            });
            saveDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener(){
                public void onClick(DialogInterface dialog, int which){
                    dialog.cancel();
                }
            });
            saveDialog.show();
        }
        else if(view.getId()==R.id.opacity_btn){
            //launch opacity chooser
            final Dialog seekDialog = new Dialog(this);
            seekDialog.setTitle("Opacity level:");
            seekDialog.setContentView(R.layout.opacity_chooser);
            //get ui elements
            final TextView seekTxt = (TextView)seekDialog.findViewById(R.id.opq_txt);
            final SeekBar seekOpq = (SeekBar)seekDialog.findViewById(R.id.opacity_seek);
            //set max
            seekOpq.setMax(100);
            //show current level
            int currLevel = drawView.getPaintAlpha();
            seekTxt.setText(currLevel+"%");
            seekOpq.setProgress(currLevel);
            //update as user interacts
            seekOpq.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {

                @Override
                public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                    seekTxt.setText(Integer.toString(progress)+"%");
                }

                @Override
                public void onStartTrackingTouch(SeekBar seekBar) {}

                @Override
                public void onStopTrackingTouch(SeekBar seekBar) {}

            });
            //listen for clicks on ok
            Button opqBtn = (Button)seekDialog.findViewById(R.id.opq_ok);
            opqBtn.setOnClickListener(new OnClickListener(){
                @Override
                public void onClick(View v) {
                    drawView.setPaintAlpha(seekOpq.getProgress());
                    seekDialog.dismiss();
                }
            });
            //show dialog
            seekDialog.show();
        }
    }

}

Answer 1

你已经以正确的方式实现了所有的东西，但我只是想建议你尝试下面的代码，也许它会对你有所帮助。

public void clearCanvas() {
        drawPath.reset();
        invalidate();
}

尝试使用此方法代替 setErase()，上述方法用于清除您使用触摸创建的路径。您可以在此方法中将所有值重置为默认值。