CompassMiniView.java

package cgeo.geocaching.ui;

import cgeo.geocaching.R;
import cgeo.geocaching.location.Geopoint;
import cgeo.geocaching.settings.Settings;
import cgeo.geocaching.utils.AngleUtils;

import android.support.annotation.NonNull;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PaintFlagsDrawFilter;
import android.util.AttributeSet;
import android.view.View;

public final class CompassMiniView extends View {
    private Geopoint targetCoords = null;
    private float azimuth = 0;
    private float heading = 0;
    /**
     * remember the last state of drawing so we can avoid repainting for very small changes
     */
    private float lastDrawnAzimuth;

    /**
     * bitmap shared by all instances of the view
     */
    private static Bitmap compassArrow;
    /**
     * bitmap width
     */
    private static int compassArrowWidth;
    /**
     * bitmap height
     */
    private static int compassArrowHeight;
    /**
     * view instance counter for bitmap recycling
     */
    private static int instances = 0;

    /**
     * pixel size of the square arrow bitmap
     */
    private static final int ARROW_BITMAP_SIZE = 21;
    private static final PaintFlagsDrawFilter FILTER_SET = new PaintFlagsDrawFilter(0, Paint.FILTER_BITMAP_FLAG);
    private static final float MINIMUM_ROTATION_DEGREES_FOR_REPAINT = 5;
    private float azimuthRelative;

    public CompassMiniView(final Context context) {
        super(context);
    }

    public CompassMiniView(final Context context, final AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();
        if (instances++ == 0) {
            final int drawable = isInEditMode() || !Settings.isLightSkin() ? R.drawable.compass_arrow_mini_white : R.drawable.compass_arrow_mini_black;
            compassArrow = BitmapFactory.decodeResource(getResources(), drawable);
            compassArrowWidth = compassArrow.getWidth();
            compassArrowHeight = compassArrow.getWidth();
        }
    }

    @Override
    public void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (--instances == 0) {
            compassArrow.recycle();
        }
    }

    public void setTargetCoords(final Geopoint point) {
        targetCoords = point;
    }

    void updateAzimuth(final float azimuth) {
        this.azimuth = azimuth;
        updateDirection();
    }

    void updateHeading(final float heading) {
        this.heading = heading;
        updateDirection();
    }

    void updateCurrentCoords(@NonNull final Geopoint currentCoords) {
        if (targetCoords == null) {
            return;
        }

        heading = currentCoords.bearingTo(targetCoords);
        updateDirection();
    }

    private void updateDirection() {
        if (compassArrow == null || compassArrow.isRecycled()) {
            return;
        }

        azimuthRelative = AngleUtils.normalize(azimuth - heading);

        // avoid updates on very small changes, which are not visible to the user
        final float change = Math.abs(azimuthRelative - lastDrawnAzimuth);
        if (change < MINIMUM_ROTATION_DEGREES_FOR_REPAINT) {
            return;
        }

        // compass margins
        final int marginLeft = (getWidth() - compassArrowWidth) / 2;
        final int marginTop = (getHeight() - compassArrowHeight) / 2;

        invalidate(marginLeft, marginTop, marginLeft + compassArrowWidth, marginTop + compassArrowHeight);
    }

    @Override
    protected void onDraw(final Canvas canvas) {
        super.onDraw(canvas);

        lastDrawnAzimuth = azimuthRelative;

        // compass margins
        final int canvasCenterX = getWidth() / 2;
        final int canvasCenterY = getHeight() / 2;

        final int marginLeft = (getWidth() - compassArrowWidth) / 2;
        final int marginTop = (getHeight() - compassArrowHeight) / 2;

        canvas.setDrawFilter(FILTER_SET);
        canvas.rotate(-azimuthRelative, canvasCenterX, canvasCenterY);
        canvas.drawBitmap(compassArrow, marginLeft, marginTop, null);
    }

    @Override
    protected void onMeasure(final int widthMeasureSpec, final int heightMeasureSpec) {
        setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec));
    }

    private int measureWidth(final int measureSpec) {
        final int specMode = MeasureSpec.getMode(measureSpec);
        final int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            return specSize;
        }

        int result = ARROW_BITMAP_SIZE + getPaddingLeft() + getPaddingRight();

        if (specMode == MeasureSpec.AT_MOST) {
            result = Math.min(result, specSize);
        }

        return result;
    }

    private int measureHeight(final int measureSpec) {
        final int specMode = MeasureSpec.getMode(measureSpec);
        final int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            return specSize;
        }

        int result = ARROW_BITMAP_SIZE + getPaddingTop() + getPaddingBottom();

        if (specMode == MeasureSpec.AT_MOST) {
            result = Math.min(result, specSize);
        }

        return result;
    }
}