/**
* CLASS: Scroller (extends Object)
* AUTHOR: danpost (greenfoot.org username)
* DATE: November 11, 2016
* MODIFIED: December 22, 2016 (fixed 'scroll' method for limited no-image scrolling)
* MODIFIED: February 21, 2017 (fixed scroll offsets for unlimited no-image scrolling)
*
* DESCRIPTION: This is a support class for a scrolling world.
* It contains two constructors;
* one for unlimited scrolling and one for limited scrolling.
* Both constructors have an 'image' parameter.
* Because image manipulation can hog up CPU time, it is important to remember that
* it is better not to have a scrolling background image
* (having an Actor for the background is probably worse
* than having the background scroll).
* For unlimited scrolling using a background image,
* the smaller that background image to be tiled, the better.
* Making the viewport (the size of the world that is visible)
* smaller can help in CPU expense, also.
* Scrolling worlds should be unbounded,
* allowing actors to move beyond the visible area.
* Ensuring that actors are removed from the world if no longer needed
* when out of view will help to prevent lag, as well.
*
* It is the responsibility of the World object that creates a Scroller object
* to determine when to scroll and by how much.
*/
​
import greenfoot.*;
public class Scroller
{
private World world; // view window world
private GreenfootImage scrollImage; // scrolling image
private boolean limited; // flag to indicate whether scrolling is limited or not
private int scrolledX, scrolledY; // current scrolled distances
private int wide, high; // dimensions of scrolling area or of image to wrap
/**
* This constructor is for an unlimited scrolling world;
* If 'image' is null, the background won't change; else the given image is wrapped
*
* @param viewWorld the world that scrolling will be performed on
* @param image the background image (tiled, if needed; wrapped when scrolling)
*/
public Scroller(World viewWorld, GreenfootImage image)
{
world = viewWorld;
scrollImage = image;
if (image != null)
{
wide = image.getWidth();
high = image.getHeight();
}
scroll(0, 0); // sets initial background image
}
/**
* This constructor is for a limited scrolling world;
* If 'image' is smaller than the given total scrolling area, it will be tiled
* If 'image' is null, the background will not change
*
* @param viewWorld the world that scrolling will be performed on
* @param image the background image (tiled, if needed) to fill the scrolling area
* @param wide the width of the visible area encompassed through scrolling;
* the given value must be at least equal to the width of 'viewWorld' and
* is given in world cells (not in pixels)
* @param high the height of the visible area encompassed through scrolling;
* the given value must be at least equal to the height of 'viewWorld' and
* is given in world cells (not in pixels)
*/
public Scroller(World viewWorld, GreenfootImage image, int wide, int high)
{
this.wide = wide;
this.high = high;
limited = true;
world = viewWorld;
if (image != null)
{
// create an image as large as scrolling area; tiled, if needed
int cSize = world.getCellSize();
scrollImage = new GreenfootImage(wide*cSize, high*cSize);
for (int x=0; x<wide*cSize; x+= image.getWidth())
for (int y=0; y<high*cSize; y+=image.getHeight())
scrollImage.drawImage(image, x, y);
// set initial background image
scroll(0, 0);
}
}
/**
* performs scrolling on 'world' by the given horizontal and vertical offsets;
* if 'limited' is false, requested distances are actual scrolling distances;
* if 'limited' is true, the distances may be adjusted due to scrolling limits;
*
* @param dsx the requested distance to shift everything horizontally
* @param dsy the requested distance to shift everything vertically
*/
public void scroll(int dsx, int dsy)
{
// adjust scroll amounts and scroll background image
if (limited)
{
// calculate limits of scrolling
int maxX = wide-world.getWidth();
int maxY = high-world.getHeight();
// apply limits to distances to scroll
if (scrolledX+dsx < 0) dsx = -scrolledX;
if (scrolledX+dsx >= maxX) dsx = maxX-scrolledX;
if (scrolledY+dsy < 0) dsy = -scrolledY;
if (scrolledY+dsy >= maxY) dsy = maxY-scrolledY;
// update scroll positions
scrolledX += dsx;
scrolledY += dsy;
// scroll background image
if (scrollImage != null)
{
world.getBackground().drawImage
(
scrollImage,
-scrolledX*world.getCellSize(),
-scrolledY*world.getCellSize()
);
}
}
else // unlimited image wrapping
{
// update scroll positions
scrolledX += dsx;
scrolledY += dsy;
// scroll background image
if (scrollImage != null)
{
// create working variables of scroll positions
int imageX = scrolledX*world.getCellSize();
int imageY = scrolledY*world.getCellSize();
// get near-zero starting positions for drawing 'scrollImage'
imageX = imageX%wide;
imageY = imageY%high;
// adjust negative values as needed
if (imageX < 0) imageX += wide;
if (imageY < 0) imageY += high;
// create image of appropriate size and tile fill 'scrollImage' onto it
GreenfootImage hold = new GreenfootImage(scrollImage);
hold.drawImage(scrollImage, -imageX, -imageY);
if (imageX > 0) hold.drawImage(scrollImage, wide-imageX, -imageY);
if (imageY > 0) hold.drawImage(scrollImage, -imageX, high-imageY);
if (imageX > 0 && imageY > 0)
hold.drawImage(scrollImage, wide-imageX, high-imageY);
// set image to background of 'world'
world.setBackground(hold);
}
}
// adjust position of all actors (that can move with 'setLocation')
for (Object obj : world.getObjects(null))
{
Actor actor = (Actor) obj;
actor.setLocation(actor.getX()-dsx, actor.getY()-dsy);
}
}
/**
* getter method for the current total scrolled distance horizontally
*
* @return the current total offset of horizontal scrolling
*/
public int getScrolledX()
{
return scrolledX;
}
/**
* getter method for the current total scrolled distance vertically
*
* @return the current total offset of vertical scrolling
*/
public int getScrolledY()
{
return scrolledY;
}
}