How to draw a path with variable stroke width
My code is basically from this example (http://corner.squareup.com/2010/07/smooth-signatures.html) and Google APIs (FingerPaint) but now I want to use the class VelocityTracker in order to change the stroke width depending on the speed of my finger.
I thought I could split a path into smaller parts but I didn't find any examples. There's also this second post (http://corner.squareup.com/2012/07/smoother-signatures.html) but I do neither have a specific bezier curve class nor do I collect all the points in an ArrayList so their example for adjusting stroke width is not very helpful.
Does anyone have an idea how to handle this? I started to learn code two weeks ago so I'm pretty new in all this stuff.
Edit: I tried to implement the velocity of my MotionEvents and I used LogCat to track the current velocity while running the app. It did work out but when I tried to use the velocity as part of the parameter for mPaint.setStrokeWidth I did not get what I actually wanted. The width of the path I draw on my canvas was changing all the time from the moment I started drawing a line till I moved my finger up. So that's why I want to split a path into smaller parts because as it is now, only the last tracked velocity affects the strokeWidth.
public class SignatureView extends View {
private static final String TAG = SignatureView.class.getSimpleName();
private static final float STROKE_WIDTH = 10;
private static final float HALF_STROKE_WIDTH = STROKE_WIDTH / 2;
private final double TOUCH_TOLERANCE = 5;
private int h = getResources().getDisplayMetrics().heightPixels;
private int w = getResources().getDisplayMetrics().widthPixels;
private Path mPath = new Path();
private Paint mPaint = new Paint();
private Paint mBitmapPaint = new Paint(Paint.DITHER_FLAG);
private Bitmap mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
private Canvas mCanvas = new Canvas(mBitmap);
private float mX, mY;
private float lastTouchX, lastTouchY;
private final RectF dirtyRect = new RectF();
public SignatureView(Context context, AttributeSet attrs) {
super(context, attrs);
mPaint.setAntiAlias(true);
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeWidth(INITIAL_STROKE_WIDTH);
Log.d(TAG, "TOUCH_TOLERANCE = " +TOUCH_TOLERANCE);
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float eventX = event.getX();
float eventY = event.getY();
int historySize = event.getHistorySize();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
resetDirtyRect(eventX, eventY);
mPath.reset();
mPath.moveTo(eventX, eventY);
mX = eventX;
mY = eventY;
break;
case MotionEvent.ACTION_MOVE:
float dx = Math.abs(eventX - mX);
float dy = Math.abs(eventY - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (eventX + mX)/2, (eventY + mY)/2);
mX = eventX;
mY = eventY;
}
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
}
break;
case MotionEvent.ACTION_UP:
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
}
mPath.lineTo(mX, mY);
mCanvas.drawPath(mPath, mPaint);
mPath.reset();
break;
default:
Log.d(TAG, "Ignored touch event: " + event.toString());
return false;
}
// Include half the stroke width to avoid clipping.
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;
}
private void expandDirtyRect(float historicalX, float historicalY) {
if (historicalX < dirtyRect.left) {
dirtyRect.left = historicalX;
} else if (historicalX > dirtyRect.right) {
dirtyRect.right = historicalX;
}
if (historicalY < dirtyRect.top) {
dirtyRect.top = historicalY;
} else if (historicalY > dirtyRect.bottom) {
dirtyRect.bottom = historicalY;
}
}
private void resetDirtyRect(float eventX, float eventY) {
dirtyRect.left = Math.min(lastTouchX, eventX);
dirtyRect.right = Math.max(lastTouchX, eventX);
dirtyRect.top = Math.min(lastTouchY, eventY);
dirtyRect.bottom = Math.max(lastTouchY, eventY);
}
}
Answer
You can use split your path object every time your stroke value changes depending on velocity. In you SignatureView class add
private Path mPath = new Path();
ArrayList<Path> mPaths = new ArrayList<Path>();
and take another ArrayList to keep stroke value for each path
ArrayList<int> strokes = new ArrayList<int>();
add a variable lastStroke along with lastTouchX and lastTouchY. I will recommend you to make lastStroke of type int.
private int lastStroke = -1; //give an initial value
now your onTouchEvent method should be something like this
@Override
public boolean onTouchEvent(MotionEvent event) {
float eventX = event.getX();
float eventY = event.getY();
int historySize = event.getHistorySize();
int eventStroke= //calculate stroke size with velocity and make it between 1-10 or any range you seem fit
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
resetDirtyRect(eventX, eventY);
mPath.reset();
mPath.moveTo(eventX, eventY);
mX = eventX;
mY = eventY;
break;
case MotionEvent.ACTION_MOVE:
float dx = Math.abs(eventX - mX);
float dy = Math.abs(eventY - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
if(lastStroke != evetnStroke){
mPath = new Path();
mPath.moveTo(mX,mY);
mPaths.Add(mPath);
mStrokes.Add(eventStroke);
}
mPath.quadTo(mX, mY, (eventX + mX)/2, (eventY + mY)/2);
mX = eventX;
mY = eventY;
}
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
}
break;
case MotionEvent.ACTION_UP:
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
}
mPath.lineTo(mX, mY);
break;
default:
Log.d(TAG, "Ignored touch event: " + event.toString());
return false;
}
// Include half the stroke width to avoid clipping.
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;
lastStroke = eventStroke;
return true;
}
and your ondraw method would be
@Override
protected void onDraw(Canvas canvas) {
for(int i=0; i<mPaths.size();i++){
mPaint.setStrokeWidth(strokes.get(i));
canvas.drawPath(mPaths.get(i), mPaint);
}
}
this is the basic idea. you need to modify it to make it work.