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POCanvas - zooming in, shifting, and scaling on Android
 

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    <p>I'm currently implementing a draw function on a webview image (the elephant below). I don't have a problem drawing on it but the zoom function does some funky stuff (2nd image below) on the drawing. When I zoom in, the drawing doesn't zoom but rather shifts over. Drawing at zoomed also doesn't work. My code is below:</p> <p><img src="https://i.stack.imgur.com/NB5Ui.png" alt="Normal"></p> <p><img src="https://i.stack.imgur.com/eGJnX.png" alt="enter image description here"></p> <pre><code>@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.save(); canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint); canvas.drawPath(drawPath, drawPaint); canvas.scale(mScaleFactor, mScaleFactor); canvas.restore(); clipBounds = canvas.getClipBounds(); } @Override public boolean onTouchEvent(MotionEvent event) { mScaleDetector.onTouchEvent(event); float touchX = event.getX() / mScaleFactor + clipBounds.left; float touchY = event.getY() / mScaleFactor + clipBounds.top; if (Deal.on) 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: drawCanvas.drawPath(drawPath, drawPaint); drawPath.reset(); break; default: return false; } else { super.onTouchEvent(event); } invalidate(); return true; } public class ScaleGestureListener extends SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureDetector detector) { mScaleFactor *= detector.getScaleFactor(); // Don't let the object get too small or too large. mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f)); invalidate(); return true; } } </code></pre> <p><strong>Edit</strong>: I managed to get the canvas to redraw with zooming using the GestureDetector's scale factor. Additionally, I have a switch that toggles from drawing to zooming/webview controls. A problem that I run into is that double tap on WebView doesn't trigger the onScale gesture. Which means the canvas doesn't get redrawn and shifts on the zoom in. </p> <p>I need to implement a feature that detects how much the scale factor is affected by the double tap zoom in. If anyone can suggest a solution to that. Here's the update code:</p> <pre><code>@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); clipBounds = canvas.getClipBounds(); canvas.save(); drawPaint.setStrokeWidth(8/mScaleFactor); canvas.scale(mScaleFactor, mScaleFactor, 0, 0); canvas.drawPath(drawPath, drawPaint); canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint); canvas.restore(); } @Override public boolean onTouchEvent(MotionEvent event) { pointerCount = event.getPointerCount(); mScaleDetector.onTouchEvent(event); float touchX = (event.getX() + clipBounds.left) / mScaleFactor; float touchY = (event.getY() + clipBounds.top) / mScaleFactor; if (Deal.on){ if (event.getPointerCount() &gt; 1){ return false; } 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: drawCanvas.drawPath(drawPath, drawPaint); drawPath.reset(); break; default: return false; } } else { super.onTouchEvent(event); } invalidate(); return true; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { // Try for a width based on our minimum int minw = getPaddingLeft() + getPaddingRight() + getSuggestedMinimumWidth(); int w = resolveSizeAndState(minw, widthMeasureSpec, 1); //int minh = MeasureSpec.getSize(w) - (int)mTextWidth + getPaddingBottom() + getPaddingTop(); int h = resolveSizeAndState(MeasureSpec.getSize(w), heightMeasureSpec, 0); setMeasuredDimension(w, h); } public class ScaleGestureListener extends SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureDetector detector) { // Don't let the object get too small or too large. if(Deal.on == false) { mScaleFactor *= detector.getScaleFactor(); mScaleFactor = Math.max(1f, Math.min(mScaleFactor, 20.0f)); } invalidate(); return true; } } </code></pre>
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    1. COdid you try performing the scale before you do any drawing with the canvas?
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      1. USGil Moshayof
    2. COAnd the question is? Why drawing isn't scaled or why it doesn't work? Obviously, You do the drawing with the same paint every time, so why it should be zoomed?
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    3. COWhy are you zooming at all on doubleTap, and where is that implemented? You have to change the scaleFactor accordingly if you do.
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      1. USTore Rudberg
 

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