path: root/src/com/android/mail/preferences/notifications/ColorPickerView.java

/*
 * Copyright (C) 2010 Daniel Nilsson
 * Copyright (C) 2015 The CyanogenMod 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.android.mail.preferences.notifications;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ComposeShader;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.PorterDuff.Mode;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.Paint.Align;
import android.graphics.Paint.Style;
import android.graphics.Shader.TileMode;
import android.os.Build;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Displays a color picker to the user and allow them to select a color. A
 * slider for the alpha channel is also available. Enable it by setting
 * setAlphaSliderVisible(boolean) to true.
 *
 * @author Daniel Nilsson
 */
public class ColorPickerView extends View {

    public interface OnColorChangedListener {
        public void onColorChanged(int color);
    }

    private final static int PANEL_SAT_VAL = 0;
    private final static int PANEL_HUE = 1;
    private final static int PANEL_ALPHA = 2;

    /**
     * The width in pixels of the border surrounding all color panels.
     */
    private final static float BORDER_WIDTH_PX = 1;

    /**
     * The width in dp of the hue panel.
     */
    private float HUE_PANEL_WIDTH = 30f;
    /**
     * The height in dp of the alpha panel
     */
    private float ALPHA_PANEL_HEIGHT = 20f;
    /**
     * The distance in dp between the different color panels.
     */
    private float PANEL_SPACING = 10f;
    /**
     * The radius in dp of the color palette tracker circle.
     */
    private float PALETTE_CIRCLE_TRACKER_RADIUS = 5f;
    /**
     * The dp which the tracker of the hue or alpha panel will extend outside of
     * its bounds.
     */
    private float RECTANGLE_TRACKER_OFFSET = 2f;

    private static float mDensity = 1f;

    private OnColorChangedListener mListener;

    private Paint mSatValPaint;
    private Paint mSatValTrackerPaint;

    private Paint mHuePaint;
    private Paint mHueTrackerPaint;

    private Paint mAlphaPaint;
    private Paint mAlphaTextPaint;

    private Paint mBorderPaint;

    private Shader mValShader;
    private Shader mSatShader;
    private Shader mHueShader;
    private Shader mAlphaShader;

    private int mAlpha = 0xff;
    private float mHue = 360f;
    private float mSat = 0f;
    private float mVal = 0f;

    private String mAlphaSliderText = "Alpha";
    private int mSliderTrackerColor = 0xff1c1c1c;
    private int mBorderColor = 0xff6E6E6E;
    private boolean mShowAlphaPanel = false;

    /*
     * To remember which panel that has the "focus" when processing hardware
     * button data.
     */
    private int mLastTouchedPanel = PANEL_SAT_VAL;

    /**
     * Offset from the edge we must have or else the finger tracker will get
     * clipped when it is drawn outside of the view.
     */
    private float mDrawingOffset;

    /*
     * Distance form the edges of the view of where we are allowed to draw.
     */
    private RectF mDrawingRect;

    private RectF mSatValRect;
    private RectF mHueRect;
    private RectF mAlphaRect;

    private AlphaPatternDrawable mAlphaPattern;

    private Point mStartTouchPoint = null;

    public ColorPickerView(Context context) {
        this(context, null);
    }

    public ColorPickerView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ColorPickerView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        mDensity = getContext().getResources().getDisplayMetrics().density;
        PALETTE_CIRCLE_TRACKER_RADIUS *= mDensity;
        RECTANGLE_TRACKER_OFFSET *= mDensity;
        HUE_PANEL_WIDTH *= mDensity;
        ALPHA_PANEL_HEIGHT *= mDensity;
        PANEL_SPACING = PANEL_SPACING * mDensity;

        mDrawingOffset = calculateRequiredOffset();
        initPaintTools();

        // Needed for receiving track ball motion events.
        setFocusableInTouchMode(true);
        setFocusable(true);
        setClickable(true);
    }

    private void initPaintTools() {
        mSatValPaint = new Paint();
        mSatValTrackerPaint = new Paint();
        mHuePaint = new Paint();
        mHueTrackerPaint = new Paint();
        mAlphaPaint = new Paint();
        mAlphaTextPaint = new Paint();
        mBorderPaint = new Paint();

        mSatValTrackerPaint.setStyle(Style.STROKE);
        mSatValTrackerPaint.setStrokeWidth(2f * mDensity);
        mSatValTrackerPaint.setAntiAlias(true);

        mHueTrackerPaint.setColor(mSliderTrackerColor);
        mHueTrackerPaint.setStyle(Style.STROKE);
        mHueTrackerPaint.setStrokeWidth(2f * mDensity);
        mHueTrackerPaint.setAntiAlias(true);

        mAlphaTextPaint.setColor(0xff1c1c1c);
        mAlphaTextPaint.setTextSize(14f * mDensity);
        mAlphaTextPaint.setAntiAlias(true);
        mAlphaTextPaint.setTextAlign(Align.CENTER);
        mAlphaTextPaint.setFakeBoldText(true);
    }

    private float calculateRequiredOffset() {
        float offset = Math.max(PALETTE_CIRCLE_TRACKER_RADIUS, RECTANGLE_TRACKER_OFFSET);
        offset = Math.max(offset, BORDER_WIDTH_PX * mDensity);

        return offset * 1.5f;
    }

    private int[] buildHueColorArray() {
        int[] hue = new int[361];

        int count = 0;
        for (int i = hue.length - 1; i >= 0; i--, count++) {
            hue[count] = Color.HSVToColor(new float[] {
                    i, 1f, 1f
            });
        }
        return hue;
    }

    @Override
    public void setEnabled(boolean enabled) {
        super.setEnabled(enabled);
        postInvalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (mDrawingRect.width() <= 0 || mDrawingRect.height() <= 0) {
            return;
        }
        drawSatValPanel(canvas);
        drawHuePanel(canvas);
        drawAlphaPanel(canvas);
    }

    private void drawSatValPanel(Canvas canvas) {
        final RectF rect = mSatValRect;
        int rgb = Color.HSVToColor(new float[] {
                mHue, 1f, 1f
        });

        if (BORDER_WIDTH_PX > 0) {
            mBorderPaint.setColor(mBorderColor);
            canvas.drawRect(mDrawingRect.left, mDrawingRect.top, rect.right + BORDER_WIDTH_PX,
                    rect.bottom + BORDER_WIDTH_PX, mBorderPaint);
        }

        // On Honeycomb+ we need to use software rendering to create the shader properly
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        }

        // Get the overlaying gradients ready and create the ComposeShader
        if (mValShader == null) {
            mValShader = new LinearGradient(rect.left, rect.top, rect.left, rect.bottom,
                    0xffffffff, 0xff000000, TileMode.CLAMP);
        }
        mSatShader = new LinearGradient(rect.left, rect.top, rect.right, rect.top,
                0xffffffff, rgb, TileMode.CLAMP);
        ComposeShader mShader = new ComposeShader(mValShader, mSatShader, Mode.MULTIPLY);
        mSatValPaint.setShader(mShader);
        canvas.drawRect(rect, mSatValPaint);

        if (isEnabled()) {
            Point p = satValToPoint(mSat, mVal);
            mSatValTrackerPaint.setColor(0xff000000);
            canvas.drawCircle(p.x, p.y, PALETTE_CIRCLE_TRACKER_RADIUS - 1f * mDensity,
                    mSatValTrackerPaint);

            mSatValTrackerPaint.setColor(0xffdddddd);
            canvas.drawCircle(p.x, p.y, PALETTE_CIRCLE_TRACKER_RADIUS, mSatValTrackerPaint);
        }
    }

    private void drawHuePanel(Canvas canvas) {
        final RectF rect = mHueRect;

        if (BORDER_WIDTH_PX > 0) {
            mBorderPaint.setColor(mBorderColor);
            canvas.drawRect(rect.left - BORDER_WIDTH_PX,
                    rect.top - BORDER_WIDTH_PX,
                    rect.right + BORDER_WIDTH_PX,
                    rect.bottom + BORDER_WIDTH_PX,
                    mBorderPaint);
        }

        if (mHueShader == null) {
            mHueShader = new LinearGradient(rect.left, rect.top, rect.left, rect.bottom,
                    buildHueColorArray(), null, TileMode.CLAMP);
            mHuePaint.setShader(mHueShader);
        }

        canvas.drawRect(rect, mHuePaint);

        if (isEnabled()) {
            float rectHeight = 4 * mDensity / 2;

            Point p = hueToPoint(mHue);

            RectF r = new RectF();
            r.left = rect.left - RECTANGLE_TRACKER_OFFSET;
            r.right = rect.right + RECTANGLE_TRACKER_OFFSET;
            r.top = p.y - rectHeight;
            r.bottom = p.y + rectHeight;

            canvas.drawRoundRect(r, 2, 2, mHueTrackerPaint);
        }
    }

    private void drawAlphaPanel(Canvas canvas) {
        if (!mShowAlphaPanel || mAlphaRect == null || mAlphaPattern == null) {
            return;
        }

        final RectF rect = mAlphaRect;

        if (BORDER_WIDTH_PX > 0) {
            mBorderPaint.setColor(mBorderColor);
            canvas.drawRect(rect.left - BORDER_WIDTH_PX,
                    rect.top - BORDER_WIDTH_PX,
                    rect.right + BORDER_WIDTH_PX,
                    rect.bottom + BORDER_WIDTH_PX,
                    mBorderPaint);
        }

        mAlphaPattern.draw(canvas);

        float[] hsv = new float[] {
                mHue, mSat, mVal
        };
        int color = Color.HSVToColor(hsv);
        int acolor = Color.HSVToColor(0, hsv);

        mAlphaShader = new LinearGradient(rect.left, rect.top, rect.right, rect.top,
                color, acolor, TileMode.CLAMP);

        mAlphaPaint.setShader(mAlphaShader);

        canvas.drawRect(rect, mAlphaPaint);

        if (isEnabled()) {
            if (mAlphaSliderText != null && mAlphaSliderText != "") {
                canvas.drawText(mAlphaSliderText, rect.centerX(), rect.centerY() + 4 * mDensity,
                        mAlphaTextPaint);
            }

            float rectWidth = 4 * mDensity / 2;
            Point p = alphaToPoint(mAlpha);

            RectF r = new RectF();
            r.left = p.x - rectWidth;
            r.right = p.x + rectWidth;
            r.top = rect.top - RECTANGLE_TRACKER_OFFSET;
            r.bottom = rect.bottom + RECTANGLE_TRACKER_OFFSET;

            canvas.drawRoundRect(r, 2, 2, mHueTrackerPaint);
        }
    }

    private Point hueToPoint(float hue) {
        final RectF rect = mHueRect;
        final float height = rect.height();

        Point p = new Point();
        p.y = (int) (height - (hue * height / 360f) + rect.top);
        p.x = (int) rect.left;
        return p;
    }

    private Point satValToPoint(float sat, float val) {

        final RectF rect = mSatValRect;
        final float height = rect.height();
        final float width = rect.width();

        Point p = new Point();

        p.x = (int) (sat * width + rect.left);
        p.y = (int) ((1f - val) * height + rect.top);

        return p;
    }

    private Point alphaToPoint(int alpha) {
        final RectF rect = mAlphaRect;
        final float width = rect.width();

        Point p = new Point();
        p.x = (int) (width - (alpha * width / 0xff) + rect.left);
        p.y = (int) rect.top;
        return p;
    }

    private float[] pointToSatVal(float x, float y) {
        final RectF rect = mSatValRect;
        float[] result = new float[2];
        float width = rect.width();
        float height = rect.height();

        if (x < rect.left) {
            x = 0f;
        } else if (x > rect.right) {
            x = width;
        } else {
            x = x - rect.left;
        }

        if (y < rect.top) {
            y = 0f;
        } else if (y > rect.bottom) {
            y = height;
        } else {
            y = y - rect.top;
        }

        result[0] = 1.f / width * x;
        result[1] = 1.f - (1.f / height * y);
        return result;
    }

    private float pointToHue(float y) {
        final RectF rect = mHueRect;
        float height = rect.height();

        if (y < rect.top) {
            y = 0f;
        } else if (y > rect.bottom) {
            y = height;
        } else {
            y = y - rect.top;
        }
        return 360f - (y * 360f / height);
    }

    private int pointToAlpha(int x) {
        final RectF rect = mAlphaRect;
        final int width = (int) rect.width();

        if (x < rect.left) {
            x = 0;
        } else if (x > rect.right) {
            x = width;
        } else {
            x = x - (int) rect.left;
        }
        return 0xff - (x * 0xff / width);
    }

    @Override
    public boolean onTrackballEvent(MotionEvent event) {
        if (!isEnabled()) {
            return super.onTrackballEvent(event);
        }

        float x = event.getX();
        float y = event.getY();
        boolean update = false;

        if (event.getAction() == MotionEvent.ACTION_MOVE) {
            switch (mLastTouchedPanel) {
                case PANEL_SAT_VAL:
                    float sat,
                    val;
                    sat = mSat + x / 50f;
                    val = mVal - y / 50f;
                    if (sat < 0f) {
                        sat = 0f;
                    } else if (sat > 1f) {
                        sat = 1f;
                    }

                    if (val < 0f) {
                        val = 0f;
                    } else if (val > 1f) {
                        val = 1f;
                    }
                    mSat = sat;
                    mVal = val;
                    update = true;
                    break;
                case PANEL_HUE:
                    float hue = mHue - y * 10f;
                    if (hue < 0f) {
                        hue = 0f;
                    } else if (hue > 360f) {
                        hue = 360f;
                    }
                    mHue = hue;
                    update = true;
                    break;
                case PANEL_ALPHA:
                    if (!mShowAlphaPanel || mAlphaRect == null) {
                        update = false;
                    } else {
                        int alpha = (int) (mAlpha - x * 10);
                        if (alpha < 0) {
                            alpha = 0;
                        } else if (alpha > 0xff) {
                            alpha = 0xff;
                        }
                        mAlpha = alpha;
                        update = true;
                    }
                    break;
            }
        }

        if (update) {
            if (mListener != null) {
                mListener.onColorChanged(Color.HSVToColor(mAlpha, new float[] {
                        mHue, mSat, mVal
                }));
            }
            invalidate();
            return true;
        }
        return super.onTrackballEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (!isEnabled()) {
            return super.onTouchEvent(event);
        }

        boolean update = false;

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mStartTouchPoint = new Point((int) event.getX(), (int) event.getY());
                update = moveTrackersIfNeeded(event);
                break;
            case MotionEvent.ACTION_MOVE:
                update = moveTrackersIfNeeded(event);
                break;
            case MotionEvent.ACTION_UP:
                mStartTouchPoint = null;
                update = moveTrackersIfNeeded(event);
                break;
        }

        if (update) {
            requestFocus();
            if (mListener != null) {
                mListener.onColorChanged(Color.HSVToColor(mAlpha, new float[] {
                        mHue, mSat, mVal
                }));
            }
            invalidate();
            return true;
        }

        return super.onTouchEvent(event);
    }

    private boolean moveTrackersIfNeeded(MotionEvent event) {

        if (mStartTouchPoint == null)
            return false;

        boolean update = false;
        int startX = mStartTouchPoint.x;
        int startY = mStartTouchPoint.y;

        if (mHueRect.contains(startX, startY)) {
            mLastTouchedPanel = PANEL_HUE;
            mHue = pointToHue(event.getY());
            update = true;
        } else if (mSatValRect.contains(startX, startY)) {
            mLastTouchedPanel = PANEL_SAT_VAL;
            float[] result = pointToSatVal(event.getX(), event.getY());
            mSat = result[0];
            mVal = result[1];
            update = true;
        } else if (mAlphaRect != null && mAlphaRect.contains(startX, startY)) {
            mLastTouchedPanel = PANEL_ALPHA;
            mAlpha = pointToAlpha((int) event.getX());
            update = true;
        }

        return update;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int width = 0;
        int height = 0;

        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        int widthAllowed = MeasureSpec.getSize(widthMeasureSpec);
        int heightAllowed = MeasureSpec.getSize(heightMeasureSpec);

        widthAllowed = chooseWidth(widthMode, widthAllowed);
        heightAllowed = chooseHeight(heightMode, heightAllowed);

        if (!mShowAlphaPanel) {
            height = (int) (widthAllowed - PANEL_SPACING - HUE_PANEL_WIDTH);

            // If calculated height (based on the width) is more than the
            // allowed height.
            if (height > heightAllowed && heightMode != MeasureSpec.UNSPECIFIED) {
                height = heightAllowed;
                width = (int) (height + PANEL_SPACING + HUE_PANEL_WIDTH);
            } else {
                width = widthAllowed;
            }
        } else {

            width = (int) (heightAllowed - ALPHA_PANEL_HEIGHT + HUE_PANEL_WIDTH);

            if (width > widthAllowed && widthMode != MeasureSpec.UNSPECIFIED) {
                width = widthAllowed;
                height = (int) (widthAllowed - HUE_PANEL_WIDTH + ALPHA_PANEL_HEIGHT);
            } else {
                height = heightAllowed;
            }
        }
        setMeasuredDimension(width, height);
    }

    private int chooseWidth(int mode, int size) {
        if (mode == MeasureSpec.AT_MOST || mode == MeasureSpec.EXACTLY) {
            return size;
        } else { // (mode == MeasureSpec.UNSPECIFIED)
            return getPrefferedWidth();
        }
    }

    private int chooseHeight(int mode, int size) {
        if (mode == MeasureSpec.AT_MOST || mode == MeasureSpec.EXACTLY) {
            return size;
        } else { // (mode == MeasureSpec.UNSPECIFIED)
            return getPrefferedHeight();
        }
    }

    private int getPrefferedWidth() {
        int width = getPrefferedHeight();
        if (mShowAlphaPanel) {
            width -= (PANEL_SPACING + ALPHA_PANEL_HEIGHT);
        }
        return (int) (width + HUE_PANEL_WIDTH + PANEL_SPACING);
    }

    private int getPrefferedHeight() {
        int height = (int) (200 * mDensity);
        if (mShowAlphaPanel) {
            height += PANEL_SPACING + ALPHA_PANEL_HEIGHT;
        }
        return height;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        mDrawingRect = new RectF();
        mDrawingRect.left = mDrawingOffset + getPaddingLeft();
        mDrawingRect.right = w - mDrawingOffset - getPaddingRight();
        mDrawingRect.top = mDrawingOffset + getPaddingTop();
        mDrawingRect.bottom = h - mDrawingOffset - getPaddingBottom();

        setUpSatValRect();
        setUpHueRect();
        setUpAlphaRect();
    }

    private void setUpSatValRect() {
        final RectF dRect = mDrawingRect;
        float panelSide = dRect.height() - BORDER_WIDTH_PX * 2;

        if (mShowAlphaPanel) {
            panelSide -= PANEL_SPACING + ALPHA_PANEL_HEIGHT;
        }

        float left = dRect.left + BORDER_WIDTH_PX;
        float top = dRect.top + BORDER_WIDTH_PX;
        float bottom = top + panelSide;
        float right = left + panelSide;
        mSatValRect = new RectF(left, top, right, bottom);
    }

    private void setUpHueRect() {
        final RectF dRect = mDrawingRect;

        float left = dRect.right - HUE_PANEL_WIDTH + BORDER_WIDTH_PX;
        float top = dRect.top + BORDER_WIDTH_PX;
        float bottom = dRect.bottom - BORDER_WIDTH_PX
                - (mShowAlphaPanel ? (PANEL_SPACING + ALPHA_PANEL_HEIGHT) : 0);
        float right = dRect.right - BORDER_WIDTH_PX;

        mHueRect = new RectF(left, top, right, bottom);
    }

    private void setUpAlphaRect() {
        if (!mShowAlphaPanel) {
            return;
        }

        final RectF dRect = mDrawingRect;
        float left = dRect.left + BORDER_WIDTH_PX;
        float top = dRect.bottom - ALPHA_PANEL_HEIGHT + BORDER_WIDTH_PX;
        float bottom = dRect.bottom - BORDER_WIDTH_PX;
        float right = dRect.right - BORDER_WIDTH_PX;

        mAlphaRect = new RectF(left, top, right, bottom);
        mAlphaPattern = new AlphaPatternDrawable((int) (5 * mDensity));
        mAlphaPattern.setBounds(Math.round(mAlphaRect.left), Math
                .round(mAlphaRect.top), Math.round(mAlphaRect.right), Math
                .round(mAlphaRect.bottom));
    }

    /**
     * Set a OnColorChangedListener to get notified when the color selected by
     * the user has changed.
     *
     * @param listener
     */
    public void setOnColorChangedListener(OnColorChangedListener listener) {
        mListener = listener;
    }

    /**
     * Set the color of the border surrounding all panels.
     *
     * @param color
     */
    public void setBorderColor(int color) {
        mBorderColor = color;
        invalidate();
    }

    /**
     * Get the color of the border surrounding all panels.
     */
    public int getBorderColor() {
        return mBorderColor;
    }

    /**
     * Get the current color this view is showing.
     *
     * @return the current color.
     */
    public int getColor() {
        return Color.HSVToColor(mAlpha, new float[] {
                mHue, mSat, mVal
        });
    }

    /**
     * Set the color the view should show.
     *
     * @param color The color that should be selected.
     */
    public void setColor(int color) {
        setColor(color, false);
    }

    /**
     * Set the color this view should show.
     *
     * @param color The color that should be selected.
     * @param callback If you want to get a callback to your
     *            OnColorChangedListener.
     */
    public void setColor(int color, boolean callback) {
        int alpha = Color.alpha(color);
        int red = Color.red(color);
        int blue = Color.blue(color);
        int green = Color.green(color);
        float[] hsv = new float[3];

        Color.RGBToHSV(red, green, blue, hsv);
        mAlpha = alpha;
        mHue = hsv[0];
        mSat = hsv[1];
        mVal = hsv[2];

        if (callback && mListener != null) {
            mListener.onColorChanged(Color.HSVToColor(mAlpha, new float[] {
                    mHue, mSat, mVal
            }));
        }
        invalidate();
    }

    /**
     * Get the drawing offset of the color picker view. The drawing offset is
     * the distance from the side of a panel to the side of the view minus the
     * padding. Useful if you want to have your own panel below showing the
     * currently selected color and want to align it perfectly.
     *
     * @return The offset in pixels.
     */
    public float getDrawingOffset() {
        return mDrawingOffset;
    }

    /**
     * Set if the user is allowed to adjust the alpha panel. Default is false.
     * If it is set to false no alpha will be set.
     *
     * @param visible
     */
    public void setAlphaSliderVisible(boolean visible) {
        if (mShowAlphaPanel != visible) {
            mShowAlphaPanel = visible;

            /*
             * Reset all shader to force a recreation. Otherwise they will not
             * look right after the size of the view has changed.
             */
            mValShader = null;
            mSatShader = null;
            mHueShader = null;
            mAlphaShader = null;
            requestLayout();
        }

    }

    public boolean isAlphaSliderVisible() {
        return mShowAlphaPanel;
    }

    public void setSliderTrackerColor(int color) {
        mSliderTrackerColor = color;
        mHueTrackerPaint.setColor(mSliderTrackerColor);
        invalidate();
    }

    public int getSliderTrackerColor() {
        return mSliderTrackerColor;
    }

    /**
     * Set the text that should be shown in the alpha slider. Set to null to
     * disable text.
     *
     * @param res string resource id.
     */
    public void setAlphaSliderText(int res) {
        String text = getContext().getString(res);
        setAlphaSliderText(text);
    }

    /**
     * Set the text that should be shown in the alpha slider. Set to null to
     * disable text.
     *
     * @param text Text that should be shown.
     */
    public void setAlphaSliderText(String text) {
        mAlphaSliderText = text;
        invalidate();
    }

    /**
     * Get the current value of the text that will be shown in the alpha slider.
     *
     * @return
     */
    public String getAlphaSliderText() {
        return mAlphaSliderText;
    }
}