我正在创建一个在 Canvas 上绘图的应用程序。为了绘图，我将笔颜色设置为黑色。
用于笔按钮
int black = Color.BLACK;
mDrawPaint = new DrawPaint(Capture.this, null,black);
DrawPaint 扩展 View 的地方
现在要创建橡皮擦，我只是将笔颜色更改为白色，这是 Canvas 的背景颜色。像这样
橡皮擦按钮
int white = Color.WHITE;
mDrawPaint = new DrawPaint(Capture.this, null,white);
但是如果我再次选择笔颜色为黑色的笔按钮并在 Canvas 上绘制一些东西，它会再次自动重绘我在删除之前绘制的先前绘制的内容。橡皮擦也擦掉了一个大的矩形区域。请向我解释出了什么问题。谢谢。
这是 DrawPaint 构造函数
public DrawPaint(Context context, AttributeSet attrs, int color) {
super(context, attrs);
this.destroyDrawingCache();
paint.setAntiAlias(true);
paint.setColor(color);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeWidth(STROKE_WIDTH);
}
public boolean onTouchEvent(MotionEvent event) {
eventX = event.getX();
eventY = event.getY();
button1.setEnabled(true);
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
path.moveTo(eventX, eventY);
lastTouchX = eventX;
lastTouchY = eventY;
return true;
case MotionEvent.ACTION_MOVE:
case MotionEvent.ACTION_UP:
resetDirtyRect(eventX, eventY);
int historySize = event.getHistorySize();
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
path.lineTo(historicalX, historicalY);
}
path.lineTo(eventX, eventY);
break;
default:
debug("Ignored touch event: " + event.toString());
return false;
}
invalidate((int) (dirtyRect.left - HALF_STROKE_WIDTH),
(int) (dirtyRect.top - HALF_STROKE_WIDTH),
(int) (dirtyRect.right + HALF_STROKE_WIDTH),
(int) (dirtyRect.bottom + HALF_STROKE_WIDTH));
lastTouchX = eventX;
lastTouchY = eventY;
return true;
}
最佳答案
对于橡皮擦，您可以使用此代码...
mPaint.setMaskFilter(null);
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
关于那个方形颜色问题...
看看这个.. 这是具有删除、模糊和浮雕效果的 Canvas 绘图的最佳示例...
public class FingerText extends Activity
implements ColorPickerDialog.OnColorChangedListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new MyView(this));
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
//this is the line that sets the initial pen color
mPaint.setColor(inkColor);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(2);
}
private Paint mPaint;
private Bitmap mBitmap;
private boolean inkChosen;
private int bgColor = 0xFFFFFFFF; //set initial bg color var to white
private int inkColor = 0xFF000000; //set initial ink color var to black
public void colorChanged(int color) {
//This is the implementation of the interface from colorpickerdialog.java
if (inkChosen){
mPaint.setColor(color);
inkColor = color;
}
else {
mBitmap.eraseColor (color);
bgColor = color;
//set the color to the user's last ink color choice
mPaint.setColor(inkColor);
}
}
public class MyView extends View {
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;
public MyView(Context c) {
super(c);
mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
//this sets the bg color for the bitmap
mBitmap.eraseColor (bgColor);
mCanvas = new Canvas(mBitmap);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
@Override
protected void onDraw(Canvas canvas) {
//this is the line that changes the bg color in the initial canvas
canvas.drawColor(bgColor);
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
}
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;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// 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;
}
}
private static final int BG_COLOR_ID = Menu.FIRST;
private static final int INK_MENU_ID = Menu.FIRST + 1;
private static final int CLEAR_MENU_ID = Menu.FIRST + 2;
private static final int ERASER_MENU_ID = Menu.FIRST + 3;
private static final int SEND_MENU_ID = Menu.FIRST + 4;
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
menu.add(0, BG_COLOR_ID, 0, "Background Color").setShortcut('3', 'b');
menu.add(0, INK_MENU_ID, 0, "Ink Color").setShortcut('4', 'c');
menu.add(0, CLEAR_MENU_ID, 0, "Clear All").setShortcut('5', 'e');
menu.add(0, ERASER_MENU_ID, 0, "Eraser").setShortcut('6', 'x');
menu.add(0, SEND_MENU_ID, 0, "Send").setShortcut('7', 's');
/**** Is this the mechanism to extend with filter effects?
Intent intent = new Intent(null, getIntent().getData());
intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
menu.addIntentOptions(
Menu.ALTERNATIVE, 0,
new ComponentName(this, NotesList.class),
null, intent, 0, null);
*****/
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
super.onPrepareOptionsMenu(menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
mPaint.setXfermode(null);
mPaint.setAlpha(0xFF);
switch (item.getItemId()) {
case BG_COLOR_ID:
new ColorPickerDialog(this, this, mPaint.getColor()).show();
inkChosen = false;
return true;
case INK_MENU_ID:
new ColorPickerDialog(this, this, mPaint.getColor()).show();
//remember the user's last ink choice color so we can revert after eraser
//to background color change -- otherwise ink is last bg color
inkColor = mPaint.getColor();
inkChosen = true;
return true;
case CLEAR_MENU_ID:
mBitmap.eraseColor (bgColor);
return true;
case ERASER_MENU_ID:
//set pen color to bg color for 'erasing'
mPaint.setColor(bgColor);
return true;
case SEND_MENU_ID:
/* TODO need to decide whether to save image locally
* and how to make it available if so. really only need to
* save if we want to let users view later, or pick a
* previous message to send again
*/
// this try-catch block creates a private file and an
// inputstream pointing to it for reading
FileInputStream ifs;
try {
FileOutputStream fs = openFileOutput("message_image", Context.MODE_PRIVATE);
mBitmap.compress(CompressFormat.PNG, 100, fs);
ifs = openFileInput("message_image");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return true;
}
// inserts file pointed to by ifs into image gallery
String url = Images.Media.insertImage(getContentResolver(),
BitmapFactory.decodeStream(ifs),
"Message image1", "Message image");
// alternative: inserts mBitmap into image gallery
/* String url = Images.Media.insertImage(getContentResolver(),
mBitmap, "Message image1", "Message image");
*/
// creates the Intent to open the messaging app
// with the image at url attached
Intent sendIntent = new Intent(Intent.ACTION_SEND);
sendIntent.putExtra("sms_body", "Message created using FingerText");
sendIntent.putExtra(Intent.EXTRA_STREAM, Uri.parse(url));
sendIntent.setType("image/png");
startActivity(sendIntent);
/* TODO delete the image from the content provider
* following line deletes the image, but too soon!
*/
// getContentResolver().delete(Uri.parse(url), null, null);
//this resets canvas after send
//could also reset to last user settings w/o var resets
bgColor = 0xFFFFFFFF; //set bg color var back to white
inkColor = 0xFF000000; //set ink color var back to black
mBitmap.eraseColor (bgColor);
return true;
}
return super.onOptionsItemSelected(item);
}
关于android - Android View 中的橡皮擦，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12816442/