Android Canvas Drawing Line

Question

I am creating a basic drawing application. The following functions are used to draw the line.

public void touchEventLine(MotionEvent event){ Log.e("Canvas","Line Specific Event"); float x = event.getX(); float y = event.getY(); switch (event.getAction()){ case MotionEvent.ACTION_DOWN: Log.e("Canvas","Line Specific Event: Action Down"); startX=x; startY=y; mPath.moveTo(startX,startY); Log.e("Canvas","Line Specific Event: Moved to X:"+startX+" Y:"+startY); mX=x; mY=y; invalidate(); break; case MotionEvent.ACTION_MOVE: Log.e("Canvas","Line Specific Event: Action Move"); endX=x; endY=y; drawLine(endX,endY); Log.e("Canvas","Line Specific Event: Drawing From X:"+startX+" Y:"+startY+" to X:"+endX+" Y:"+endY); paths.add(mPath); colorsMap.put(mPath,selectedColor); mPath = new Path(); isDrawing++; invalidate(); if(isDrawing>1) { paths.remove(paths.size() - 2); isDrawing--; } break; case MotionEvent.ACTION_UP: Log.e("Canvas","Line Specific Event: Action Up"); endX=x; endY=y; drawLine(endX,endY); paths.add(mPath); colorsMap.put(mPath,selectedColor); mPath = new Path(); paths.remove(paths.size() - 2); invalidate(); isDrawing=0; break; } }

and the drawLine() function is

private void drawLine(float x2,float y2){ mPath.lineTo(x2,y2); invalidate(); Log.e("Canvas","Line Drawn"); }

and my onDraw() function is

protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawBitmap(mBitmap, 0, 0, canvasPaint); canvas.drawPath(mPath,drawPaint); for (Path p : paths) { int curColor= colorsMap.get(p); drawPaint.setColor(curColor); canvas.drawPath(p, drawPaint); } Log.e("Canvas","OnDraw() Called"); }

My problem is that the line is drawing from top left corner of screen. I believe it is (0,0). I used the same logic for drawing circle and rectangle and both working fine. Is there any mistake in my logic.? How can I fix this..? Thanks in advance

top left of the canvas is (0,0) as you guessed but what's the problem? — lelloman
– lelloman, Commented Aug 31, 2016 at 7:18
No.. because I implemented an undo function which will work only if I use path. — Ruthwik Warrier
– Ruthwik Warrier, Commented Aug 31, 2016 at 7:19
@lelloman The problem is that I want to draw line from (startX,startY) to (endX, endY) — Ruthwik Warrier
– Ruthwik Warrier, Commented Aug 31, 2016 at 7:21
@RuthwikWarrier canvas.drawBitmap(mBitmap, left, top, canvasPaint); .You are giving left and top as 0 so it will draw from the left corner of screen right ?. Change your left to startX — Sunil Sunny
– Sunil Sunny, Commented Aug 31, 2016 at 7:33

MehDi · Accepted Answer · 2016-09-04 20:41:48Z

It's easy. you should call

path.moveTo(firstPoint_X, firstPoint_y);

at the first of the drawing.

(after each line that you call mPath = new Path(); )

if you don't call

path.moveTo

method after you make a new instance of Path class,by default it start drawing from position(0,0) of screen

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