Android - How do I get raw touch screen information?

Question

I'm working on a painting application for Android and I'd like to use raw data from the device's touch screen to adjust the user's paint brush as they draw. I've seen other apps for Android (iSteam, for example) where the size of the brush is based on the size of your fingerprint on the screen. As far as painting apps go, that would be a huge feature.

Is there a way to get this data? I've googled for quite a while, but I haven't found any source demonstrating it. I know it's possible, because Dolphin Browser adds multi-touch support to the Hero without any changes beneath the application level. You must be able to get a 2D matrix of raw data or something...

I'd really appreciate any help I can get!

Answer 1

There are some properties in the Motion Event class. You can use the getSize() method to find the size of the object. The Motion Event class also gives access to pressure, coordinates etc...

Answer 2

If you check the APIDemos in the SDK there's a simple paitning app called TouchPaint

package com.example.android.apis.graphics;

It uses the following to draw on the canvas

@Override public boolean onTouchEvent(MotionEvent event) {
            int action = event.getAction();
            mCurDown = action == MotionEvent.ACTION_DOWN
                    || action == MotionEvent.ACTION_MOVE;
            int N = event.getHistorySize();
            for (int i=0; i<N; i++) {
                //Log.i("TouchPaint", "Intermediate pointer #" + i);
                drawPoint(event.getHistoricalX(i), event.getHistoricalY(i),
                        event.getHistoricalPressure(i),
                        event.getHistoricalSize(i));
            }
            drawPoint(event.getX(), event.getY(), event.getPressure(),
                    event.getSize());
            return true;
        }

private void drawPoint(float x, float y, float pressure, float size) {
            //Log.i("TouchPaint", "Drawing: " + x + "x" + y + " p="
            //        + pressure + " s=" + size);
            mCurX = (int)x;
            mCurY = (int)y;
            mCurPressure = pressure;
            mCurSize = size;
            mCurWidth = (int)(mCurSize*(getWidth()/3));
            if (mCurWidth < 1) mCurWidth = 1;
            if (mCurDown && mBitmap != null) {
                int pressureLevel = (int)(mCurPressure*255);
                mPaint.setARGB(pressureLevel, 255, 255, 255);
                mCanvas.drawCircle(mCurX, mCurY, mCurWidth, mPaint);
                mRect.set(mCurX-mCurWidth-2, mCurY-mCurWidth-2,
                        mCurX+mCurWidth+2, mCurY+mCurWidth+2);
                invalidate(mRect);
            }
            mFadeSteps = 0;
        }

Hope that helps :)

Answer 3

I'm working on something similar, and I'd suggest looking at the Canvas and Paint classes as well. Looking at getHistorySize() in Motion Event might also be helpful for figuring out how long a particular stroke has been in play.