In case of drawing square, the user touch on the screen to mark the start position, and move, and release on the end position. We have to keep displaying the updated square. But if we draw the rect on the canvasMaster, it will full of rect when user touch and move.
In this example, we create two overlay ImageViews, have same dimension. Also additional bitmap and canvas for the extra ImagewView. When ACTION_DOWN detected, we mark the starting position. When ACTION_MOVE, we draw rect on the extra canvasDrawingPane, not the canvasMaster. Such that we can clear and re-draw the canvas everytime. And finally when ACTION_UP, simple draw the extra bitmap on canvasMaster.
package com.example.androiddrawbitmap;
import java.io.FileNotFoundException;
import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff.Mode;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
public class MainActivity extends Activity {
Button btnLoadImage;
TextView textSource;
ImageView imageResult, imageDrawingPane;
final int RQS_IMAGE1 = 1;
Uri source;
Bitmap bitmapMaster;
Canvas canvasMaster;
Bitmap bitmapDrawingPane;
Canvas canvasDrawingPane;
projectPt startPt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnLoadImage = (Button)findViewById(R.id.loadimage);
textSource = (TextView)findViewById(R.id.sourceuri);
imageResult = (ImageView)findViewById(R.id.result);
imageDrawingPane = (ImageView)findViewById(R.id.drawingpane);
btnLoadImage.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View arg0) {
Intent intent = new Intent(Intent.ACTION_PICK,
android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(intent, RQS_IMAGE1);
}});
imageResult.setOnTouchListener(new OnTouchListener(){
@Override
public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
int x = (int) event.getX();
int y = (int) event.getY();
switch(action){
case MotionEvent.ACTION_DOWN:
textSource.setText("ACTION_DOWN- " + x + " : " + y);
startPt = projectXY((ImageView)v, bitmapMaster, x, y);
break;
case MotionEvent.ACTION_MOVE:
textSource.setText("ACTION_MOVE- " + x + " : " + y);
drawOnRectProjectedBitMap((ImageView)v, bitmapMaster, x, y);
break;
case MotionEvent.ACTION_UP:
textSource.setText("ACTION_UP- " + x + " : " + y);
drawOnRectProjectedBitMap((ImageView)v, bitmapMaster, x, y);
finalizeDrawing();
break;
}
/*
* Return 'true' to indicate that the event have been consumed.
* If auto-generated 'false', your code can detect ACTION_DOWN only,
* cannot detect ACTION_MOVE and ACTION_UP.
*/
return true;
}});
}
class projectPt{
int x;
int y;
projectPt(int tx, int ty){
x = tx;
y = ty;
}
}
private projectPt projectXY(ImageView iv, Bitmap bm, int x, int y){
if(x<0 || y<0 || x > iv.getWidth() || y > iv.getHeight()){
//outside ImageView
return null;
}else{
int projectedX = (int)((double)x * ((double)bm.getWidth()/(double)iv.getWidth()));
int projectedY = (int)((double)y * ((double)bm.getHeight()/(double)iv.getHeight()));
return new projectPt(projectedX, projectedY);
}
}
private void drawOnRectProjectedBitMap(ImageView iv, Bitmap bm, int x, int y){
if(x<0 || y<0 || x > iv.getWidth() || y > iv.getHeight()){
//outside ImageView
return;
}else{
int projectedX = (int)((double)x * ((double)bm.getWidth()/(double)iv.getWidth()));
int projectedY = (int)((double)y * ((double)bm.getHeight()/(double)iv.getHeight()));
//clear canvasDrawingPane
canvasDrawingPane.drawColor(Color.TRANSPARENT, Mode.CLEAR);
Paint paint = new Paint();
paint.setStyle(Paint.Style.STROKE);
paint.setColor(Color.WHITE);
paint.setStrokeWidth(3);
canvasDrawingPane.drawRect(startPt.x, startPt.y, projectedX, projectedY, paint);
imageDrawingPane.invalidate();
textSource.setText(x + ":" + y + "/" + iv.getWidth() + " : " + iv.getHeight() + "\n" +
projectedX + " : " + projectedY + "/" + bm.getWidth() + " : " + bm.getHeight()
);
}
}
private void finalizeDrawing(){
canvasMaster.drawBitmap(bitmapDrawingPane, 0, 0, null);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
Bitmap tempBitmap;
if(resultCode == RESULT_OK){
switch (requestCode){
case RQS_IMAGE1:
source = data.getData();
textSource.setText(source.toString());
try {
//tempBitmap is Immutable bitmap,
//cannot be passed to Canvas constructor
tempBitmap = BitmapFactory.decodeStream(
getContentResolver().openInputStream(source));
Config config;
if(tempBitmap.getConfig() != null){
config = tempBitmap.getConfig();
}else{
config = Config.ARGB_8888;
}
//bitmapMaster is Mutable bitmap
bitmapMaster = Bitmap.createBitmap(
tempBitmap.getWidth(),
tempBitmap.getHeight(),
config);
canvasMaster = new Canvas(bitmapMaster);
canvasMaster.drawBitmap(tempBitmap, 0, 0, null);
imageResult.setImageBitmap(bitmapMaster);
//Create bitmap of same size for drawing
bitmapDrawingPane = Bitmap.createBitmap(
tempBitmap.getWidth(),
tempBitmap.getHeight(),
config);
canvasDrawingPane = new Canvas(bitmapDrawingPane);
imageDrawingPane.setImageBitmap(bitmapDrawingPane);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
break;
}
}
}
}
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:autoLink="web"
android:text="http://android-er.blogspot.com/"
android:textStyle="bold" />
<Button
android:id="@+id/loadimage"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Load Image 1" />
<TextView
android:id="@+id/sourceuri"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/result"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:background="@android:color/background_dark"
android:scaleType="centerInside" />
<ImageView
android:id="@+id/drawingpane"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:scaleType="centerInside"
android:layout_alignLeft="@id/result"
android:layout_alignTop="@id/result"
android:layout_alignRight="@id/result"
android:layout_alignBottom="@id/result"/>
</RelativeLayout>
</LinearLayout>
Download the files.Correction: To make sure bitmapDrawingPane have alpha channel, create it with Config.ARGB_8888.
//Create bitmap of same size for drawing
bitmapDrawingPane = Bitmap.createBitmap(
tempBitmap.getWidth(),
tempBitmap.getHeight(),
Config.ARGB_8888);
more: Something about processing images in Android
