我编写了一个带有Canvas的Android应用程序，用于使用手写笔绘图。它运作良好。当我按下手写笔的上部功能键时，我想通过刷过文本来擦除图形。正常的绘图是黑色的，所以我想用白色擦除（在黑线的顶部）。我的问题是，当我按下手写笔的上部功能键（即所有线条都是白色）时，所有线条都会改变颜色，而不是仅仅将新的绘制线条涂成白色。
另一种选择是删除路径中的元素以进行擦除。如果有人有解决方案，我也会很高兴。
布局如下：
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff"
tools:context="StylusBaselineA">
<inf.ethz.ch.affectivestudy.CanvasView
android:id="@+id/baselineACanvas"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:textColor="#FFFFFF" />
</android.support.constraint.ConstraintLayout>
CanvasView课程如下：
public class CanvasView extends View {
public int width;
public int height;
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Path mPathErase;
Context context;
private Paint mPaint;
private Paint mPaintErase;
private float mX, mY;
private static final float TOLERANCE = 5;
private boolean erase = false;
public CanvasView(Context c, AttributeSet attrs) {
super(c, attrs);
context = c;
// we set a new Path
mPath = new Path();
mPathErase = new Path();
// and we set a new Paint with the desired attributes
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeWidth(4f);
mPaintErase = new Paint();
mPaintErase.setAntiAlias(true);
mPaintErase.setColor(Color.WHITE);
mPaintErase.setStyle(Paint.Style.STROKE);
mPaintErase.setStrokeJoin(Paint.Join.ROUND);
mPaintErase.setStrokeWidth(4f);
}
// override onSizeChanged
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
// your Canvas will draw onto the defined Bitmap
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
// override onDraw
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// draw the mPath with the mPaint on the canvas when onDraw
if (erase) {
canvas.drawPath(mPathErase, mPaintErase);
} else {
canvas.drawPath(mPath, mPaint);
}
}
// when ACTION_DOWN start touch according to the x,y values
private void startTouch(float x, float y) {
if (erase) {
mPathErase.moveTo(x, y);
} else {
mPath.moveTo(x, y);
}
mX = x;
mY = y;
}
// when ACTION_MOVE move touch according to the x,y values
private void moveTouch(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOLERANCE || dy >= TOLERANCE) {
if (erase) {
mPathErase.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
} else {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
}
mX = x;
mY = y;
}
}
public void clearCanvas() {
mPath.reset();
mPathErase.reset();
invalidate();
}
// when ACTION_UP stop touch
private void upTouch() {
if (erase) {
mPathErase.lineTo(mX, mY);
} else {
mPath.lineTo(mX, mY);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
if (event.getToolType(0) == MotionEvent.TOOL_TYPE_ERASER) {
// Upper function key of stylus
erase = true;
} else if (event.getToolType(0) == MotionEvent.TOOL_TYPE_FINGER) {
// Touch input
erase = false;
return false;
} else {
erase = false;
}
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
startTouch(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
moveTouch(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
upTouch();
invalidate();
break;
}
return true;
}
}
答案 0 :(得分：2)
试试这个。
public class CanvasActivity extends AppCompatActivity {
private Paint mPaint;
View mView;
Button clear;
private Canvas mCanvas;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_canvas);
RelativeLayout layout = (RelativeLayout) findViewById(R.id.Linear_layout);
mView = new DrawingView(this);
layout.addView(mView, new LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.MATCH_PARENT));
clear= (Button) findViewById(R.id.clear);
clear.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCanvas.drawColor(Color.WHITE);
}
});
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(Color.GREEN);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(12);
}
public class DrawingView extends View {
public int width;
public int height;
private Bitmap mBitmap;
private Path mPath;
private Paint mBitmapPaint;
Context context;
private Paint circlePaint;
private Path circlePath;
public DrawingView(Context c) {
super(c);
context=c;
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
circlePaint = new Paint();
circlePath = new Path();
circlePaint.setAntiAlias(true);
circlePaint.setColor(Color.BLUE);
circlePaint.setStyle(Paint.Style.STROKE);
circlePaint.setStrokeJoin(Paint.Join.MITER);
circlePaint.setStrokeWidth(4f);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath( mPath, mPaint);
canvas.drawPath( circlePath, circlePaint);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
circlePath.reset();
circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
circlePath.reset();
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
mPath.reset();
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touch_start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
}