问题
'm developing an application in which I'm pasting images, doing drawing and painting on canvas. This app can also Scale up/down the canvas or drag it to different location. My problem is: I can't get the correct canvas coordinates after scaling or dragging the canvas. I want to draw finger paint after the canvas is scaled or dragged but unable to retrieve the right place where i've touched...
@Override
public boolean onTouchEvent(MotionEvent event) {
scaleListener.onTouchEvent(event);
synchronized(thread.getSurfaceHolder()){
switch ( event.getAction() & MotionEvent.ACTION_MASK ){
case MotionEvent.ACTION_DOWN :
// Remember our initial down event location.
savedMatrix.set(m_matrix);
start.set(event.getX() , event.getY());
mode = DRAG;
break;
case MotionEvent.ACTION_POINTER_DOWN :
oldDist = spacing(event);
if (oldDist > 10f) {
savedMatrix.set(m_matrix);
m_matrix.getValues(matrixValues);
midPoint(mid, event);
mode = ZOOM;
}
break;
case MotionEvent.ACTION_UP :
case MotionEvent.ACTION_POINTER_UP :
mode = NONE;
break;
case MotionEvent.ACTION_MOVE :
if(mode==DRAG && isDragAllowd){
m_matrix.set(savedMatrix);
rebound(event.getX() , event.getY());
}
else if(mode==ZOOM){
float newDist = spacing(event);
if (newDist > 10f){
m_matrix.set(savedMatrix);
float scale = newDist/oldDist;
m_matrix.getValues(matrixValues);
float currentScale = matrixValues[Matrix.MSCALE_X];
// limit zoom
if (scale * currentScale > maxZoom){
scale = maxZoom / currentScale;
//scale = maxZoom;
}
else if (scale * currentScale < minZoom){
scale = minZoom / currentScale;
//scale = minZoom;
}
m_matrix.postScale(scale, scale, mid.x, mid.y);
m_matrix.getValues(matrixValues);
}
}
break;
}
return true; //done with this event so consume it
}
}
@Override
protected void onDraw(Canvas canvas){
super.onDraw(canvas);
canvas.drawColor(Color.WHITE);
canvas.drawBitmap(currentBitmap, m_matrix, null);
c2.drawColor(Color.BLACK);
commandManager.executeAll(c2); // Drawing all the Paints on Canvas c2
// Overlay bitmap it's a transparent layour
canvas.drawBitmap(overlayBitmap, 0, 0, pTouch);
}
when user zoom the bitmap he is not able to draw over it , after zooming drawing doesn't happen at proper place.
回答1:
use the following equation for transformed the points, after that user will not face an any difficulty painting during zoom or after scrolling.
float f1 = (( motionEvent.getX() - m_transformedPoints[0] )/( m_transformedPoints[2] - m_transformedPoints[0] ))*currentBitmapWidth;
float f2 = (( motionEvent.getY() - m_transformedPoints[1] )/( m_transformedPoints[3] - m_transformedPoints[1] ))*currentBitmapHeight;
//calculate the transformed view in onDraw Method
this.m_transformedPoints[0] = 0.0F;
this.m_transformedPoints[1] = 0.0F;
this.m_transformedPoints[2] = currentBitmapWidth;
this.m_transformedPoints[3] = currentBitmapHeight;
this.m_matrix.mapPoints(this.m_transformedPoints);
来源：https://stackoverflow.com/questions/12312617/draw-path-with-zoom-and-darg