Bitmap that follows your finger instantly

Question

I want a bitmap to follow my finger. But when I use MotionEvent.ACTION_MOVE the bitmap lags behind. Is there a way the bitmap follows instantly (or almost instantly) your finger?

    public boolean onTouch(View v, MotionEvent me) 
{   
    // TODO Auto-generated method stub
    switch(me.getAction())
    {
    case MotionEvent.ACTION_DOWN:
        if(me.getX() > player.get_RectXPos() && me.getX() < player.get_RectXPos() + player.get_Width() && 
           me.getY() > player.get_RectYPos() && me.getY() < player.get_RectYPos() + player.get_Height())
        {
            isDown = true;
        }
        break;
    case MotionEvent.ACTION_UP:
        isDown = false;
        break;
    case MotionEvent.ACTION_MOVE:
        if(isDown == true)
        {
            player.set_xPos(me.getX());
            player.set_yPos(me.getY());
        }

        break;
    }
    return true;
}

I think you asked for this part:

    void render(Canvas canvas)
{
    m_Src = new Rect(0, 0, m_RectWidth, m_RectHeight);
    m_Dst = new Rect(m_RectX, m_RectY, m_RectX + m_RectWidth, m_RectY + m_RectHeight);
    canvas.drawBitmap(m_Bitmap, m_Src, m_Dst, null);
}

The onDraw code shouldn't be any secret here :) but gives us information what's wrong — Niko, Feb 11 '14 at 16:31
Well I have to render the bitmap everytime, because it changes its position — user3297952, Feb 11 '14 at 16:31
How are you invoking a redraw? Are you calling `invalidate()` inside `onTouch()`? — Paul Lammertsma, Feb 13 '14 at 09:03

Arnaud · Answer 1 · 2014-02-11T16:50:24.870

0

You must do some unnecessary work on your onTouch method. Because it should not be laggy if you only change its position.

Edit: You can save your Rect m_Src and m_Dst and just change their coordinates in your render. That will save a lot of work for the system and the garbage collection.

edited Feb 11 '14 at 16:50

answered Feb 11 '14 at 16:05

Arnaud

509
5
13

This ain't really an answer, you could comment the question with OP – Niko Feb 11 '14 at 16:05
That's true.. i'm kinda new here didn't know sry – Arnaud Feb 11 '14 at 16:07

score 0 · Accepted Answer · answered Feb 11 '14 at 16:36

void render(Canvas canvas)
{
m_Src = new Rect(0, 0, m_RectWidth, m_RectHeight);
m_Dst = new Rect(m_RectX, m_RectY, m_RectX + m_RectWidth, m_RectY + m_RectHeight);
canvas.drawBitmap(m_Bitmap, m_Src, m_Dst, null);
}

Here you allocate 2 Rect objects each time. You should initialize them only once and use Rect.set to change their values.

Also if your Bitmap size should not change, you could use public void drawBitmap (Bitmap bitmap, float left, float top, Paint paint) since this method doesn't do any scaling/translation to the Bitmap and should be more efficient.

score 0 · Answer 3 · answered Feb 11 '14 at 16:40

My guess is that the "onTouch" handler interrupts everytime the drawing...

Your "onDraw" routine should be located in its proper thread (maybe ASyncTask could do the job too). You'll have then to forward the x,y coordinates of your finger to the gui thread.

Type "Thread Gui Android" in google for a comprehensive example :)

Bitmap that follows your finger instantly

3 Answers3