tests/MultiDisplayTest/src/com/google/android/car/multidisplaytest/draw/CanvasView.java

/*
 * Copyright (C) 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.android.car.multidisplaytest.draw;

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 CanvasView extends View {
    private static final float TOLERANCE = 5.0f;

    private final Paint mPaint;
    private final Path mPath;
    private float mX;
    private float mY;

    public CanvasView(Context c, AttributeSet attrs) {
        super(c, attrs);

        mPath = new Path();
        mPaint = new Paint();
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeWidth(4f);
        mPaint.setColor(Color.WHITE);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(mPath, mPaint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                downTouch(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                moveTouch(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                upTouch();
                invalidate();
                break;
        }
        return true;
    }

    public void clearCanvas() {
        mPath.reset();
        invalidate();
    }

    private void moveTouch(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if (dx >= TOLERANCE || dy >= TOLERANCE) {
            // use mid-point as the control point of the bezier curve to make a smooth line
            // eg. when forming curve between three non-aligned consecutive points
            mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
            mX = x;
            mY = y;
        }
    }

    private void downTouch(float x, float y) {
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void upTouch() {
        mPath.lineTo(mX, mY);
    }
}