ScatterPlotZAxisGradient.java

package uk.org.smithfamily.mslogger.widgets;

import java.text.DecimalFormat;

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

/**
 * View used in scatter plot to display a ROYGB (Red-Orange-Yellow-Green-Blue) gradient
 */
public class ScatterPlotZAxisGradient extends View
{
    private double min;
    private double max;
    
    private Paint valuePaint;
    DecimalFormat decimalFormat;
    
    private boolean ready = false;
    private final int GRADIENT_NB_LINES = 1020;
    
    ZAxisGradient color;

    private Paint gradientPaint;
    
    /**
     * 
     * @param context
     */
    public ScatterPlotZAxisGradient(Context context)
    {
        super(context);
    }
    
    /**
     * 
     * @param context
     * @param s
     */
    public ScatterPlotZAxisGradient(Context context, AttributeSet s)
    {
        super(context, s);
        init(context);
    }

    /**
     * 
     * @param context
     * @param attr
     * @param defaultStyles
     */
    public ScatterPlotZAxisGradient(Context context, AttributeSet attr, int defaultStyles)
    {
        super(context, attr, defaultStyles);
        init(context);
    }
    
    /**
     * Initialise component that are going to be used to draw on the view
     * 
     * @param context
     */
    public void init(Context context)
    {
        gradientPaint = new Paint();
        gradientPaint.setStrokeWidth(2);
        
        color = new ZAxisGradient(1020,0);
        decimalFormat = new DecimalFormat("#.00");
        
        valuePaint = new Paint();
        valuePaint.setColor(Color.WHITE);
        valuePaint.setTextSize(14);
        valuePaint.setTextAlign(Paint.Align.LEFT);
        valuePaint.setAntiAlias(true);
    }
    
    /**
     * Initialise the view with the minimum and maximum value of the gradient
     * 
     * @param min
     * @param max
     */
    public void initWithMinMax(double min, double max)
    {
        this.min = min;
        this.max = max;
        
        this.ready  = true;
    }
    
    /**
     * Set the dimension of the view
     * 
     * @param widthSpec
     * @param heightSpec
     */
    @Override
    protected void onMeasure(int widthSpec, int heightSpec)
    {
        int measuredWidth = MeasureSpec.getSize(widthSpec);
        int measuredHeight = MeasureSpec.getSize(heightSpec);
        
        setMeasuredDimension(measuredWidth, measuredHeight);
    }
    
    /**
     * Method where everything is drawn
     * 
     * @param canvas The canvas to draw on
     */
    @Override
    protected void onDraw(Canvas canvas)
    {            
        if (ready) {
            final int height = getHeight();
            float yRescaleFactor = height / 1020f;
            
            // Draw the gradient line per line
            int y = 0;
            while (y < GRADIENT_NB_LINES)
            {
                gradientPaint.setColor(color.getColorForValue(y));
                   
                canvas.drawLine(0, y * yRescaleFactor, 20, y * yRescaleFactor, gradientPaint); 
                
                y++;
            }

            final float textHeight = valuePaint.getTextSize() + 2;
            final int nbSteps = (int) (height / textHeight);
            
            final double range = max - min;
            final double step = range / nbSteps;
            
            // Draw the scale
            for (int i = 0; i < nbSteps; i ++)
            {
                canvas.drawText(decimalFormat.format(max - (i * step)), 25, 12 + (i * textHeight), valuePaint);
            }
        }
    }

}