SpringBar.java

/*
 * Copyright 2015 chenupt
 * Copyright 2015 LuckyJayce
 *
 * 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.yuyh.library.view.viewpager.indicator.slidebar;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.View;

public class SpringBar extends View implements ScrollBar {
	private int tabWidth;
	private Paint paint;
	private Path path;
	private Point foot;
	private Point head;
	private float radiusMax;
	private float radiusMin;
	private float radiusOffset;
	private float acceleration = 0.5f;
	private float headMoveOffset = 0.6f;
	private float footMoveOffset = 1 - headMoveOffset;
	private float maxRadiusPercent;
	private float minRadiusPercent;

	public SpringBar(Context context, int springColor) {
		this(context, springColor, 0.9f, 0.35f);
	}

	public SpringBar(Context context, int springColor, float maxRadiusPercent, float minRadiusPercent) {
		super(context);
		this.maxRadiusPercent = maxRadiusPercent;
		this.minRadiusPercent = minRadiusPercent;
		foot = new Point();
		head = new Point();
		path = new Path();
		paint = new Paint();
		paint.setAntiAlias(true);
		paint.setStyle(Paint.Style.FILL_AND_STROKE);
		paint.setStrokeWidth(1);
		paint.setColor(springColor);
	}

	@Override
	public int getHeight(int tabHeight) {
		int half = tabHeight / 2;
		foot.setY(half);
		head.setY(half);
		radiusMax = half * maxRadiusPercent;
		radiusMin = half * minRadiusPercent;
		radiusOffset = radiusMax - radiusMin;
		return tabHeight;
	}

	@Override
	public int getWidth(int tabWidth) {
		this.tabWidth = tabWidth;
		if (positionOffset < 0.02f || positionOffset > 0.98f) {
			onPageScrolled(0, 0, 0);
		}
		return tabWidth + tabWidth / 2;
	}

	@Override
	public View getSlideView() {
		return this;
	}

	@Override
	public Gravity getGravity() {
		return Gravity.CENTENT_BACKGROUND;
	}

	private float positionOffset;

	@Override
	public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
		this.positionOffset = positionOffset;
		if (positionOffset < 0.02f || positionOffset > 0.98f) {
			head.setX(getOffsetX(0));
			foot.setX(getOffsetX(0));
			head.setRadius(radiusMax);
			foot.setRadius(radiusMax);
		} else {
			float radiusOffsetHead = 0.5f;
			if (positionOffset < radiusOffsetHead) {
				head.setRadius(radiusMin);
			} else {
				head.setRadius(((positionOffset - radiusOffsetHead) / (1 - radiusOffsetHead) * radiusOffset + radiusMin));
			}
			float radiusOffsetFoot = 0.5f;
			if (positionOffset < radiusOffsetFoot) {
				foot.setRadius((1 - positionOffset / radiusOffsetFoot) * radiusOffset + radiusMin);
			} else {
				foot.setRadius(radiusMin);
			}
			float headX = 0f;
			if (positionOffset > headMoveOffset) {
				float positionOffsetTemp = (positionOffset - headMoveOffset) / (1 - headMoveOffset);
				headX = (float) ((Math.atan(positionOffsetTemp * acceleration * 2 - acceleration) + (Math.atan(acceleration))) / (2 * (Math
						.atan(acceleration))));
			}
			// x
			head.setX(getOffsetX(positionOffset) - headX * getPositionDistance(position));
			float footX = 1f;
			if (positionOffset < footMoveOffset) {
				float positionOffsetTemp = positionOffset / footMoveOffset;
				footX = (float) ((Math.atan(positionOffsetTemp * acceleration * 2 - acceleration) + (Math.atan(acceleration))) / (2 * (Math
						.atan(acceleration))));
			}
			foot.setX(getOffsetX(positionOffset) - footX * getPositionDistance(position));
		}
	}

	private float getOffsetX(float positionOffset) {
		return tabWidth + tabWidth / 2 - tabWidth * (1 - positionOffset) + tabWidth / 4.0f;
	}

	private float getPositionDistance(int position) {
		return tabWidth;
	}

	@Override
	protected void onDraw(Canvas canvas) {
		makePath();
		canvas.drawColor(Color.TRANSPARENT);
		// canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.OVERLAY);
		canvas.drawPath(path, paint);
		canvas.drawCircle(head.getX(), head.getY(), head.getRadius(), paint);
		canvas.drawCircle(foot.getX(), foot.getY(), foot.getRadius(), paint);
		super.onDraw(canvas);
	}

	private void makePath() {
		float headOffsetX = (float) (foot.getRadius() * Math.sin(Math.atan((head.getY() - foot.getY()) / (head.getX() - foot.getX()))));
		float headOffsetY = (float) (foot.getRadius() * Math.cos(Math.atan((head.getY() - foot.getY()) / (head.getX() - foot.getX()))));

		float footOffsetX = (float) (head.getRadius() * Math.sin(Math.atan((head.getY() - foot.getY()) / (head.getX() - foot.getX()))));
		float footOffsetY = (float) (head.getRadius() * Math.cos(Math.atan((head.getY() - foot.getY()) / (head.getX() - foot.getX()))));

		float x1 = foot.getX() - headOffsetX;
		float y1 = foot.getY() + headOffsetY;

		float x2 = foot.getX() + headOffsetX;
		float y2 = foot.getY() - headOffsetY;

		float x3 = head.getX() - footOffsetX;
		float y3 = head.getY() + footOffsetY;

		float x4 = head.getX() + footOffsetX;
		float y4 = head.getY() - footOffsetY;

		float anchorX = (head.getX() + foot.getX()) / 2;
		float anchorY = (head.getY() + foot.getY()) / 2;

		path.reset();
		path.moveTo(x1, y1);
		path.quadTo(anchorX, anchorY, x3, y3);
		path.lineTo(x4, y4);
		path.quadTo(anchorX, anchorY, x2, y2);
		path.lineTo(x1, y1);
	}

	private class Point {

		private float x;
		private float y;
		private float radius;

		public float getX() {
			return x;
		}

		public void setX(float x) {
			this.x = x;
		}

		public float getY() {
			return y;
		}

		public void setY(float y) {
			this.y = y;
		}

		public float getRadius() {
			return radius;
		}

		public void setRadius(float radius) {
			this.radius = radius;
		}

	}
}