add some basic drawing

app/src/main/java/draw/simplemobiletools/com/MyCanvas.java

@@ -0,0 +1,79 @@
+package draw.simplemobiletools.com;
+
+import android.content.Context;
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.graphics.Path;
+import android.util.AttributeSet;
+import android.view.MotionEvent;
+import android.view.View;
+
+public class MyCanvas extends View {
+    private static final float THRESHOLD = 5;
+    private Paint paint;
+    private Path path;
+    private float startX;
+    private float startY;
+
+    public MyCanvas(Context context, AttributeSet attrs) {
+        super(context, attrs);
+
+        path = new Path();
+        paint = new Paint();
+        paint.setColor(Color.BLACK);
+        paint.setStyle(Paint.Style.STROKE);
+        paint.setStrokeWidth(5f);
+    }
+
+    @Override
+    protected void onDraw(Canvas canvas) {
+        super.onDraw(canvas);
+        canvas.drawPath(path, paint);
+    }
+
+    private void actionDown(float x, float y) {
+        path.moveTo(x, y);
+        startX = x;
+        startY = y;
+    }
+
+    private void actionMove(float x, float y) {
+        final float dx = Math.abs(x - startX);
+        final float dy = Math.abs(y - startY);
+        if (dx >= THRESHOLD || dy >= THRESHOLD) {
+            path.quadTo(startX, startY, (x + startX) / 2, (y + startY) / 2);
+            startX = x;
+            startY = y;
+        }
+    }
+
+    private void actionUp() {
+        path.lineTo(startX, startY);
+    }
+
+    @Override
+    public boolean onTouchEvent(MotionEvent event) {
+        final float x = event.getX();
+        final float y = event.getY();
+
+        switch (event.getAction()) {
+            case MotionEvent.ACTION_DOWN:
+                actionDown(x, y);
+                invalidate();
+                break;
+            case MotionEvent.ACTION_MOVE:
+                actionMove(x, y);
+                invalidate();
+                break;
+            case MotionEvent.ACTION_UP:
+                actionUp();
+                invalidate();
+                break;
+            default:
+                break;
+        }
+
+        return true;
+    }
+}