Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

Java scrolling background

Posted on 2011-02-24
3
Medium Priority
?
658 Views
Last Modified: 2012-05-11
I am creating Road Rash in a java midlet. I have come to the part where I have to create the track that scrolls towards the player. Does anyone have any idea about how to go about doing this? Could I just have the trees move towards the player to give the effect of the track and if so how would I put bends in the track.
0
Comment
Question by:tango2009
  • 2
3 Comments
 
LVL 28

Expert Comment

by:dpearson
ID: 34975984
Yes you're thinking along the right lines.  You're going to want to draw the trees closer and closer to the player (and getting larger) to give the sense of motion.

In order to draw the road you want to think in terms of scan lines.  Say the horizon is half way up the screen.  To draw the road you need to keep track of where the left and right side of the road is for each line from the midpoint of the screen down.  With each frame repaint of the game, you'd draw a line in the color of the road (or copied from a bitmap if you want more beauty at the cost of less speed) from left-to-right for that line of the screen.

On a straight road your left and right values would all be the same.  For a bend, the values would vary.

For example, say the lower half of the screen is 200 pixels and the screen is 400 pixels wide.  You'd have:

 
int[] left = new int[200] ;
int[] right = new int[200] ;

For a straight road:
for (int i =  0; i < 200 ; i++) { left[i] = 100 ; right[i] = 300 ; }

For a road with a bend:
for (int i =  0 ; i < 200 ; i++) { left[i] = i/2 ; right[i] = 200+i/2 ; }

Then to create the next frame you'd shift the road down one (or more) lines:
void nextFrame(int moveLines) {
    for (int i = 0 ; i < 200-moveLines ; i++) { left[i] = left[i+moveLines] ; right[i] = right[i+moveLines] ; }
    // Now fill in new values for left[200-movesLines] to left[200], these define the new road appearing
   // over the horizon.
}

void drawFrame() {
   for (int i = 0 ; i < 200 ; i++) {
       // Draw the road
       int y = 400-i ;
       drawLine(left[i],y, right[i],y) ;
   }
}

Open in new window


Hope that makes sense.

Doug
0
 

Author Comment

by:tango2009
ID: 34982984
What should drawLine be defined as? and should I just call the drawFrame method in the part of the code that draws the objects?
0
 
LVL 28

Accepted Solution

by:
dpearson earned 2000 total points
ID: 34985813
That was just pseudo code.

If you want details on how to use the actual drawLine method in Java there's an example here: http://www.java2s.com/Code/Java/2D-Graphics-GUI/Drawline.htm

And yes you should call the drawFrame() method in the part of the code that draws the objects.  You should draw the background first and then draw the trees etc. afterwards, so they appear to be in front of the background.

Doug
0

Featured Post

VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

If you’re thinking to yourself “That description sounds a lot like two people doing the work that one could accomplish,” you’re not alone.
When you discover the power of the R programming language, you are going to wonder how you ever lived without it! Learn why the language merits a place in your programming arsenal.
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

885 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question