Map the touch position with a mask

In previous exercise, I show how to:
- Detect touched position on a ImageView
- Get color on a specified location from ImageView's background bitmap
- Display text on a specified location in a custom View

In this step, I want to convert the touch position to a meaningful description, such as Head, Body, Heart, Hand and Foot. As show in the video here.





I make(copy) the Android Bitmap as the image source of the custom ImageView, TouchView. And re-paint the image with specified color for various part. Both images have the same size, and same pattern. Copy them in /res/drawable/ folder.

When I get the touch position from onTouchEvent() method in TouchView, I get the pixel color from the mask image, instead of get from the original image. So I can detect the touched part by comparing the mask pixel color with various specified color.

In order to compare the Android image and the mask image, I have to make both in same proportion. So I re-assign main.xml to use Anadroid:src instead of android:background. And I use fixed layout size for the FrameLayout.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<FrameLayout 
android:layout_width="384px"
android:layout_height="384px"
>

<com.exercise.AndroidDetechTouch.TouchView
android:id="@+id/myandroid"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:src="@drawable/android"
/>
<com.exercise.AndroidDetechTouch.InfoView
android:id="@+id/infoview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>

</FrameLayout>
</LinearLayout>

The custom ImageView, TouchView.java

package com.exercise.AndroidDetechTouch;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ImageView;

public class TouchView extends ImageView {

Bitmap bitmap, mask;
double bmWidth, bmHeight; 

String touchInfo;
float touchX, touchY;

String part;

public TouchView(Context context) {
super(context);
// TODO Auto-generated constructor stub
init();
}

public TouchView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
init();
}

public TouchView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// TODO Auto-generated constructor stub
init();
}

private void init(){

bitmap = ((BitmapDrawable)getDrawable()).getBitmap();
mask = BitmapFactory.decodeResource(getResources(), R.drawable.android_mask);
bmWidth = (double)bitmap.getWidth();
bmHeight = (double)bitmap.getHeight();
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),
MeasureSpec.getSize(heightMeasureSpec));
}

@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub

switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_MOVE:
touchX = event.getX();
touchY = event.getY();

long maskColor = getColor(touchX, touchY);

//Match the color in Mask bitmap
if(maskColor == Color.RED){
touchInfo = "Heart";
}else if(maskColor == Color.GREEN){
touchInfo = "Head";
}else if(maskColor == Color.BLUE){
touchInfo = "Body";
}else if(maskColor == -256){
touchInfo = "Hand";
}else if(maskColor == -16711681){
touchInfo = "Foot";
}else{
touchInfo = "";
}

((AndroidDetechTouchActivity)getContext()).updateMsg(touchInfo, touchX, touchY, (int)maskColor);
return true;

default:
return false;
}

}


private long getColor(float x, float y){

if ( x < 0 || y < 0 || x > (float)getWidth() || y > (float)getHeight()){
return 0; //Invalid, return 0
}else{
//Convert touched x, y on View to on Bitmap
int xBm = (int)(x * (bmWidth / (double)getWidth()));
int yBm = (int)(y * (bmHeight / (double)getHeight()));

return mask.getPixel(xBm, yBm);
}
}

}

InfoView.java, the wording will be display here.

package com.exercise.AndroidDetechTouch;

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

public class InfoView extends View {

String info = "";
float x = 0; //init value 
float y = 0; //init value
int color = Color.BLACK;

public InfoView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}

public InfoView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}

public InfoView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// TODO Auto-generated constructor stub
}

@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);

Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL_AND_STROKE);
paint.setColor(color);
paint.setStrokeWidth(2);
paint.setTextSize(30);

canvas.drawLine(x-10, y, x+10, y, paint);
canvas.drawLine(x, y-10, x, y+10, paint);
canvas.drawText(info, x, y, paint);

}

public void updateInfo(String t_info, float t_x, float t_y, int t_c){
info = t_info;
x = t_x;
y = t_y;
color = t_c;
invalidate();
}

public void clearInfo(){
info = "";
x = 0;
y = 0;
invalidate();
}

}

main activity, AndroidDetechTouchActivity.java

package com.exercise.AndroidDetechTouch;

import android.app.Activity;
import android.os.Bundle;

public class AndroidDetechTouchActivity extends Activity {

TouchView myAndroid;
InfoView infoView;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

myAndroid = (TouchView)findViewById(R.id.myandroid);
infoView = (InfoView)findViewById(R.id.infoview);

}

public void updateMsg(String t_info, float t_x, float t_y, int t_c){

infoView.updateInfo(t_info, t_x, t_y, t_c);

}

public void clearMsg(){

infoView.clearInfo();

}

}

Download the files.

In this example, It's difficult to align the image of a ImageView and the bitmap! I have another more flexible approach in next exercise: Map the touch position with a mask, version II.