Question

Iam beginner in android game development and i’m currently having some trouble on drawing pixels on the screen using bitmap and canvas.

Here is my code:

package com.example.arkanoid;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MotionEvent;
import android.widget.TextView;
import android.graphics.*;

public class MainActivity extends Activity {
    Bitmap  bitmap;
    Canvas canvas;
    int lastx=0, lasty=0;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        bitmap = Bitmap.createBitmap(400,400,Bitmap.Config.ARGB_8888);
        canvas = new Canvas(bitmap);
        bitmap.prepareToDraw();
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    public void drawPixel(int x, int y) {
        if(bitmap.isMutable()) {
            bitmap.setPixel(x,y,Color.rgb(100,100,100));
        }
        canvas.drawBitmap(bitmap,0,0,null);
    }

    public boolean onTouchEvent(MotionEvent event) {
        int x = (int)event.getX();
        int y = (int)event.getY();
        TextView texto = (TextView)findViewById(R.id.textView1); 
        texto.setText("X: "+x+", Y: "+y);
        if(lastx !=x || lasty !=y){
            lastx=x;
            lasty=y;
            drawPixel(x,y);
        }
    return false;
    }
}

When the function drawPixel(int x, int y) is called multiple times the application stops running:

And no pixels are drawn, so what is the error here? thanks for your time.

I forgot the LOG from LogCat, sorry:

http://txtup.co/eISoF

Answer 1

according for the logcat you uploaded, you need to check if x & y are between the bitmap size.