What is the most efficient way to do lighting for a tile based engine in Java?
Would it be putting a black background behind the tiles and changing the tiles' alpha?
Or putting a black foreground and changing alpha of that? Or anything else?
This is an example of the kind of lighting I want:
There are many ways to achieve this. Take some time before making your final decision. I will briefly sum up some techiques you could choose to use and provide some code in the end.
Hard Lighting
If you want to create a hard-edge lighting effect (like your example image),
some approaches come to my mind:
Quick and dirty (as you suggested)
Use a black background
Set the tiles' alpha values according to their darkness value
A problem is, that you can neither make a tile brighter than it was before (highlights) nor change the color of the light. Both of these are aspects which usually make lighting in games look good.
A second set of tiles
Use a second set of (black/colored) tiles
Lay these over the main tiles
Set the new tiles' alpha value depending on how strong the new color should be there.
This approach has the same effect as the first one with the advantage, that you now may color the overlay tile in another color than black, which allows for both colored lights and doing highlights.
Example:
Even though it is easy, a problem is, that this is indeed a very inefficent way. (Two rendered tiles per tile, constant recoloring, many render operations etc.)
More Efficient Approaches (Hard and/or Soft Lighting)
When looking at your example, I imagine the light always comes from a specific source tile (character, torch, etc.)
For every type of light (big torch, small torch, character lighting) you
create an image that represents the specific lighting behaviour relative to the source tile (light mask). Maybe something like this for a torch (white being alpha):
For every tile which is a light source, you render this image at the position of the source as an overlay.
To add a bit of light color, you can use e.g. 10% opaque orange instead of full alpha.
Results
Adding soft light
Soft light is no big deal now, just use more detail in light mask compared to the tiles. By using only 15% alpha in the usually black region you can add a low sight effect when a tile is not lit:
You may even easily achieve more complex lighting forms (cones etc.) just by changing the mask image.
Multiple light sources
When combining multiple light sources, this approach leads to a problem:
Drawing two masks, which intersect each other, might cancel themselves out:
What we want to have is that they add their lights instead of subtracting them.
Avoiding the problem:
Invert all light masks (with alpha being dark areas, opaque being light ones)
Render all these light masks into a temporary image which has the same dimensions as the viewport
Invert and render the new image (as if it was the only light mask) over the whole scenery.
This would result in something similar to this:
Code for the mask invert method
Assuming you render all the tiles in a BufferedImage first,
I'll provide some guidance code which resembles the last shown method (only grayscale support).
Multiple light masks for e.g. a torch and a player can be combined like this:
public BufferedImage combineMasks(BufferedImage[] images)
{
// create the new image, canvas size is the max. of all image sizes
int w, h;
for (BufferedImage img : images)
{
w = img.getWidth() > w ? img.getWidth() : w;
h = img.getHeight() > h ? img.getHeight() : h;
}
BufferedImage combined = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
// paint all images, preserving the alpha channels
Graphics g = combined.getGraphics();
for (BufferedImage img : images)
g.drawImage(img, 0, 0, null);
return combined;
}
The final mask is created and applied with this method:
public void applyGrayscaleMaskToAlpha(BufferedImage image, BufferedImage mask)
{
int width = image.getWidth();
int height = image.getHeight();
int[] imagePixels = image.getRGB(0, 0, width, height, null, 0, width);
int[] maskPixels = mask.getRGB(0, 0, width, height, null, 0, width);
for (int i = 0; i < imagePixels.length; i++)
{
int color = imagePixels[i] & 0x00ffffff; // Mask preexisting alpha
// get alpha from color int
// be careful, an alpha mask works the other way round, so we have to subtract this from 255
int alpha = (maskPixels[i] >> 24) & 0xff;
imagePixels[i] = color | alpha;
}
image.setRGB(0, 0, width, height, imagePixels, 0, width);
}
As noted, this is a primitive example. Implementing color blending might be a bit more work.
Raytracing might be the simpliest approach.
you can store which tiles have been seen (used for automapping, used for 'remember your map while being blinded', maybe for the minimap etc.)
you show only what you see - maybe a monster of a wall or a hill is blocking your view, then raytracing stops at that point
distant 'glowing objects' or other light sources (torches lava) can be seen, even if your own light source doesn't reach very far.
the length of your ray gives will be used to check amount light (fading light)
maybe you have a special sensor (ESP, gold/food detection) which would be used to find objects that are not in your view? raytrace might help as well ^^
how is this done easy?
draw a line from your player to every point of the border of your map (using Bresehhams Algorithm http://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
walk along that line (from your character to the end) until your view is blocked; at this point stop your search (or maybe do one last final iteration to see what did top you)
for each point on your line set the lighning (maybe 100% for distance 1, 70% for distance 2 and so on) and mark you map tile as visited
maybe you won't walk along the whole map, maybe it's enough if you set your raytrace for a 20x20 view?
NOTE: you really have to walk along the borders of viewport, its NOT required to trace every point.
i'm adding the line algorithm to simplify your work:
public static ArrayList<Point> getLine(Point start, Point target) {
ArrayList<Point> ret = new ArrayList<Point>();
int x0 = start.x;
int y0 = start.y;
int x1 = target.x;
int y1 = target.y;
int sx = 0;
int sy = 0;
int dx = Math.abs(x1-x0);
sx = x0<x1 ? 1 : -1;
int dy = -1*Math.abs(y1-y0);
sy = y0<y1 ? 1 : -1;
int err = dx+dy, e2; /* error value e_xy */
for(;;){ /* loop */
ret.add( new Point(x0,y0) );
if (x0==x1 && y0==y1) break;
e2 = 2*err;
if (e2 >= dy) { err += dy; x0 += sx; } /* e_xy+e_x > 0 */
if (e2 <= dx) { err += dx; y0 += sy; } /* e_xy+e_y < 0 */
}
return ret;
}
i did this whole lightning stuff some time ago, a* pathfindin feel free to ask further questions
Appendum:
maybe i might simply add the small algorithms for raytracing ^^
to get the North & South Border Point just use this snippet:
for (int x = 0; x <map.WIDTH; x++){
Point northBorderPoint = new Point(x,0);
Point southBorderPoint = new Point(x,map.HEIGHT);
rayTrace( getLine(player.getPos(), northBorderPoint), player.getLightRadius()) );
rayTrace( getLine(player.getPos(), southBorderPoint, player.getLightRadius()) );
}
and the raytrace works like this:
private static void rayTrace(ArrayList<Point> line, WorldMap map, int radius) {
//int radius = radius from light source
for (Point p: line){
boolean doContinue = true;
float d = distance(line.get(0), p);
//caclulate light linear 100%...0%
float amountLight = (radius - d) / radius;
if (amountLight < 0 ){
amountLight = 0;
}
map.setLight( p, amountLight );
if ( ! map.isViewBlocked(p) ){ //can be blockeb dy wall, or monster
doContinue = false;
break;
}
}
}
I've been into indie game development for about three years right now. The way I would do this is first of all by using OpenGL so you can get all the benefits of the graphical computing power of the GPU (hopefully you are already doing that). Suppose we start off with all tiles in a VBO, entirely lit. Now, there are several options of achieving what you want. Depending on how complex your lighting system is, you can choose a different approach.
If your light is going to be circular around the player, no matter the fact if obstacles would block the light in real life, you could choose for a lighting algorithm implemented in the vertex shader. In the vertex shader, you could compute the distance of the vertex to the player and apply some function that defines how bright things should be in function of the computed distance. Do not use alpha, but just multiply the color of the texture/tile by the lighting value.
If you want to use a custom lightmap (which is more likely), I would suggest to add an extra vertex attribute that specifies the brightness of the tile. Update the VBO if needed. Same approach goes here: multiply the pixel of the texture by the light value. If you are filling light recursively with the player position as starting point, then you would update the VBO every time the player moves.
If your lightmap depends on where the sunlight hits your level, you could combine two sort of lighting techniques. Create one vertex attribute for the sun brightness and another vertex attribute for the light emitted by light points (like a torch held by the player). Now you can combine those two values in the vertex shader. Suppose the your sun comes up and goes down like the day and night pattern. Let's say the sun brightness is sun, which is a value between 0 and 1. This value can be passed to the vertex shader as a uniform. The vertex attribute that represents the sun brightness is s and the one for light, emitted by light points is l. Then you could compute the total light for that tile like this:
tileBrightness = max(s * sun, l + flicker);
Where flicker (also a vertex shader uniform) is some kind of waving function that represents the little variants in the brightness of your light points.
This approach makes the scene dynamic without having to recreate continuously VBO's. I implemented this approach in a proof-of-concept project. It works great. You can check out what it looks like here: http://www.youtube.com/watch?v=jTcNitp_IIo. Note how the torchlight is flickering at 0:40 in the video. That is done by what I explained here.
Related
I am making a Tile based infinite world game (Similar to Notch's Minicraft) and i am trying to implement light. Here is the function i use:
The arguments it takes are the World itself, and the tiles position relative to world co-ordinates
public static Vector.Vector3f calculateLight(World w, int worldx, int worldy){
float tileLightValue = 0;
float totalLights = 0;
for(Light currentLight : BlockLighting.lights){ // for each light
float currentLightXWorldPosition = currentLight.x;
float currentLightYWorldPosition = currentLight.y;
float distanceBetweenPoints = Core.MathFunctions.getDistance(
worldx,worldy,
currentLightXWorldPosition, currentLightYWorldPosition
);
if(distanceBetweenPoints < currentLight.range){
tileLightValue += distanceBetweenPoints / 20.175f;
totalLights += 1;
}
}
float lig = Core.MathFunctions.fclamp(((tileLightValue * -2.4f) + (69.3f / 100)), 0 , 1);
if(totalLights > 0){
return new Vector.Vector3f(lig,lig,lig);
}else{
// If no lights, return 0 as to not change the ambient light.
return new Vector.Vector3f(0,0,0);
}
}
Calculations are then made by taking the light value of this function, and then adding it to the base lighting (ambient)
...
Core.MathFunctions.fclamp(daylight + light, 0, 1)
...
And produces the Intended result:
But When the lights intersect, i get this glitch :
So it has to be a mathematical issue. So im hoping someone could offer a solution to this issue or modify my code to send me in the correct direction, the best way to describe the function is:
Given a list of light points, and a position of a tile. Calculate the appropriate lighting for said tile in an infinite world, so that when it is added to the ambient lighting of the world it produces a Terraria like lighting effect.
Note the code showing the ambient light calculation (2nd code block) is more or less pseudo-code, the actual code uses the Vector3 for color calculation, and that works fine, just thought id strip it down to lessen confusion
Edit: Here is a JSFiddle using the exact same code, to illustrate the issue. So you can see it, and tinker with it!
Interactive JS Example
Despite passing equal (exactly equal) coordinates for 'adjacent' edges, I'm ending up with some strange lines between adjacent elements when scaling my grid of rendered tiles.
My tile grid rendering algorithm accepts scaled tiles, so that I can adjust the grid's visual size to match a chosen window size of the same aspect ratio, among other reasons. It seems to work correctly when scaled to exact integers, and a few non-integer values, but I get some inconsistent results for the others.
Some Screenshots:
The blue lines are the clear color showing through. The chosen texture has no transparent gaps in the tilesheet, as unused tiles are magenta and actual transparency is handled by the alpha layer. The neighboring tiles in the sheet have full opacity. Scaling is achieved by setting the scale to a normalized value obtained through a gamepad trigger between 1f and 2f, so I don't know what actual scale was applied when the shot was taken, with the exception of the max/min.
Attribute updates and entity drawing are synchronized between threads, so none of the values could have been applied mid-draw. This isn't transferred well through screenshots, but the lines don't flicker when the scale is sustained at that point, so it logically shouldn't be an issue with drawing between scale assignment (and thread locks prevent this).
Scaled to 1x:
Scaled to A, 1x < Ax < Bx :
Scaled to B, Ax < Bx < Cx :
Scaled to C, Bx < Cx < 2x :
Scaled to 2x:
Projection setup function
For setting up orthographic projection (changes only on screen size changes):
.......
float nw, nh;
nh = Display.getHeight();
nw = Display.getWidth();
GL11.glOrtho(0, nw, nh, 0, 1, -1);
orthocenter.setX(nw/2); //this is a Vector2, floats for X and Y, direct assignment.
orthocenter.setY(nh/2);
.......
For the purposes of the screenshot, nw is 512, nh is 384 (implicitly casted from int). These never change throughout the example above.
General GL drawing code
After cutting irrelevant attributes that didn't fix the problem when cut:
#Override
public void draw(float xOffset, float yOffset, float width, float height,
int glTex, float texX, float texY, float texWidth, float texHeight) {
GL11.glLoadIdentity();
GL11.glTranslatef(0.375f, 0.375f, 0f); //This is supposed to fix subpixel issues, but makes no difference here
GL11.glTranslatef(xOffset, yOffset, 0f);
if(glTex != lastTexture){
GL11.glBindTexture(GL11.GL_TEXTURE_2D, glTex);
lastTexture = glTex;
}
GL11.glBegin(GL11.GL_QUADS);
GL11.glTexCoord2f(texX,texY + texHeight);
GL11.glVertex2f(-height/2, -width/2);
GL11.glTexCoord2f(texX + texWidth,texY + texHeight);
GL11.glVertex2f(-height/2, width/2);
GL11.glTexCoord2f(texX + texWidth,texY);
GL11.glVertex2f(height/2, width/2);
GL11.glTexCoord2f(texX,texY);
GL11.glVertex2f(height/2, -width/2);
GL11.glEnd();
}
Grid drawing code (dropping the same parameters dropped from 'draw'):
//Externally there is tilesize, which contains tile pixel size, in this case 32x32
public void draw(Engine engine, Vector2 offset, Vector2 scale){
int xp, yp; //x and y position of individual tiles
for(int c = 0; c<width; c++){ //c as in column
xp = (int) (c*tilesize.a*scale.getX()); //set distance from chunk x to column x
for(int r = 0; r<height; r++){ //r as in row
if(tiles[r*width+c] <0) continue; //skip empty tiles ('air')
yp = (int) (r*tilesize.b*scale.getY()); //set distance from chunk y to column y
tileset.getFrame(tiles[r*width+c]).draw( //pull 'tile' frame from set, render.
engine, //drawing context
new Vector2(offset.getX() + xp, offset.getY() + yp), //location of tile
scale //scale of tiles
);
}
}
}
Between the tiles and the platform specific code, vectors' components are retrieved and passed along to the general drawing code as pasted earlier.
My analysis
Mathematically, each position is an exact multiple of the scale*tilesize in either the x or y direction, or both, which is then added to the offset of the grid's location. It is then passed as an offset to the drawing code, which translates that offset with glTranslatef, then draws a tile centered at that location through halving the dimensions then drawing each plus-minus pair.
This should mean that when tile 1 is drawn at, say, origin, it has an offset of 0. Opengl then is instructed to draw a quad, with the left edge at -halfwidth, right edge at +halfwidth, top edge at -halfheight, and bottom edge at +halfheight. It then is told to draw the neighbor, tile 2, with an offset of one width, so it translates from 0 to that width, then draws left edge at -halfwidth, which should coordinate-wise be exactly the same as tile1's right edge. By itself, this should work, and it does. When considering a constant scale, it breaks somehow.
When a scale is applied, it is a constant multiple across all width/height values, and mathematically shouldn't make anything change. However, it does make a difference, for what I think could be one of two reasons:
OpenGL is having issues with subpixel filling, ie filling left of a vertex doesn't fill the vertex's containing pixel space, and filling right of that same vertex also doesn't fill the vertex's containing pixel space.
I'm running into float accuracy problems, where somehow X+width/2 does not equal X+width - width/2 where width = tilewidth*scale, tilewidth is an integer, and X is a float.
I'm not really sure about how to tell which one is the problem, or how to remedy it other than to simply avoid non-integer scale values, which I'd like to be able to support. The only clue I think might apply to finding the solution is how the pattern of line gaps isn't really consistant (see how it skips tiles in some cases, only has vertical or horizontal but not both, etc). However, I don't know what this implies.
This looks like it's probably a floating point precision issue. The critical statement in your question is this:
Mathematically, each position is an exact multiple [..]
While that's mathematically true, you're dealing with limited floating point precision. Sequences of operations that should mathematically produce the same result can (and often do) produce slightly different results due to rounding errors during expression evaluation.
Specifically in your case, it looks like you're relying on identities of this form:
i * width + width/2 == (i + 1) * width - width/2
This is mathematically correct, but you can't expect to get exactly the same numbers when evaluating the values with limited floating point precision. Depending on how the small errors end up getting rounded to pixels, it can result in visual artifacts.
The only good way to avoid this is that you actually use the same values for coordinates that must be the same, instead of using calculations that mathematically produce the same results.
In the case of coordinates on a grid, you could calculate the coordinates for each grid line (tile boundary) once, and then use those values for all draw operations. Say if you have n tiles in the x-direction, you calculate all the x-values as:
x[i] = i * width;
and then when drawing tile i, use x[i] and x[i + 1] as the left and right x-coordinates.
I am making a game that has campfire objects. What I want to do is to brighten all pixels in a circle around each campfire. However, looping through every pixel and changing those within the radius is not all that efficient and makes the game run at ~7 fps. Ideas on how to either make this process efficient or simulate light differently?
I haven't written the code for the fires but this is the basic loop to check each pixel/change its brightness based on a number:
public static BufferedImage updateLightLevels(BufferedImage img, float light)
{
BufferedImage brightnessBuffer = new BufferedImage(img.getWidth(), img.getHeight(), BufferedImage.TYPE_4BYTE_ABGR);
brightnessBuffer.getGraphics().drawImage(img, 0, 0, null);
for(int i = 0; i < brightnessBuffer.getWidth(); i++)
{
for(int a = 0; a < brightnessBuffer.getHeight(); a++)
{
//get the color at the pixel
int rgb = brightnessBuffer.getRGB(i, a);
//check to see if it is transparent
int alpha = (rgb >> 24) & 0x000000FF;
if(alpha != 0)
{
//make a new color
Color rgbColor = new Color(rgb);
//turn it into an hsb color
float[] hsbCol = Color.RGBtoHSB(rgbColor.getRed(), rgbColor.getGreen(), rgbColor.getBlue(), null);
//lower it by the certain amount
//if the pixel is already darker then push it all the way to black
if(hsbCol[2] <= light)
hsbCol[2] -= (hsbCol[2]) - .01f;
else
hsbCol[2] -= light;
//turn the hsb color into a rgb color
int rgbNew = Color.HSBtoRGB(hsbCol[0], hsbCol[1], hsbCol[2]);
//set the pixel to the new color
brightnessBuffer.setRGB(i, a, rgbNew);
}
}
}
return brightnessBuffer;
}
I apologize if my code is not clean, I'm self taught.
I can give you lots of approaches.
You're currently rendering on the CPU, and you're checking every single pixel. That's hardcore brute force, and brute force isn't what the CPU is best at. It works, but as you've seen, the performance is abysmal.
I'd point you in two directions that would massively improve your performance:
Method 1 - Culling. Does every single pixel really need to have its lighting calculated? If you could instead calculate a general "ambient light", then you could paint most of the pixels in that ambient light, and then only calculate the really proper lighting for pixels closest to lights; so lights throw a "spot" effect which fades into the ambient. That way you're only ever performing checks on a few of the pixels of the screen at a time (the circle area around each light). The code you posted just looks like it paints every pixel, I'm not seeing where the "circle" dropoff is even applied.
Edit:
Instead, sweep through the lights, and just loop through local offsets of the light position.
for(Light l : Lights){
for(int x = l.getX() -LIGHT_DISTANCE, x< l.getX() + LIGHT_DISTANCE, y++){
for(int y = l.getY() - LIGHT_DISTANCE, y < l.getY() + LIGHT_DISTANCE, y++){
//calculate light
int rgb = brightnessBuffer.getRGB(x, y);
//do stuff
}
}
You may want to add a check with that method so overlapping lights don't cause a bunch of rechecks, unless you DO want that behavior (ideally those pixels would be twice as bright)
Method 2 - Offhand calculation to the GPU. There's a reason we have graphics cards; they're specifically built to be able to number crunch those situations where you really need brute force. If you can offload this process to the GPU as a shader, then it'll run licketysplit, even if you run it on every pixel several times over. This will require you to learn graphics APIs however, but if you're working in java, LibGDX makes it very painless to render using the GPU and pass off a couple shaders to the GPU.
I am uncertain about the way in which you are going about calculating light values, but I do know that using the BufferedImage.getRGB() and BufferedImage.setRGB() methods is very slow.
I would suggest accessing the pixels of the BufferedImage directly from an array (much faster IMO)
to do this:
BufferedImage lightImage = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
Raster r = lightImage.getRaster();
int[] lightPixels = ((DataBufferInt)r.getDataBuffer()).getData();
Now, changing any pixel in this array will show on your image. Note that the values used in this array are color values in the format of whatever format you defined your image with.
In this case it is TYPE_INT_ARGB meaning you will have to include the alpha value in the number when setting the coloar (RRGGBB*AA*)
Since this array is a 1D array, it is more difficult to access pixels using x and y co-ordinates. The following method is an implementation of accessing pixels from the lightPixels array more easily.
public void setLight(int x, int y,int[] array,int width, int value){
array[width*y+x] = value;
}
*note: width is the width of your level, or the width of the 2D array your level might exist as, if it was a 2D array.
You can also get pixels from the lightPixels array with a similar method, just excluding the value and returning the array[width*y+x].
It is up to you how you use the setLight() and getLight() methods but in the cases that I have encountered, using this method is much faster than using getRGB and setRGB.
Hope this helps
I'm working with sprite art, and I need to generate a polygon (array of vertices) for a collision detector.
I have a getPixel(x, y) method I can use to get the color of a pixel. I don't need any fancy color detection or anything, just solid pixels and transparent pixels. Here's what I started before my brain started to melt:
boolean[] hasColor = new boolean[size];
for (int i = 0; i < size; i++) {
int row;
row = i % width;
if ((pixmap.getPixel(i, row) != 0) || (pixmap.getPixel(row, i) != -256)) {
hasColor[i] = true;
} else {
hasColor[i] = false;
}
}
That should keep track of what pixels are empty, and what aren't. But I don't know where I should go from here.
Is there an algorithm or something I can use to help? Can someone provide input?
What you have is raster artwork.
What you need is a vector outline.
Converting from vector to raster is easy, raster to vector, not so much.
Here is one possible workflow:
Convert your artwork into a black-and-white image (like your pixel color present/not-present matrix).
Use Adobe Illustrator's "Live Trace" feature to vectorize this image.
Export the outline polygon into a format that you can read back easily.
Use this as your input for the collision detection.
Here's another approach:
A) Assume that the outline looks like a hexagon, like this:
*****
* *
* *
* *
* *
* *
*****
B) Define "fit" as the goodness of an outline, calculated by checking what percentage of the pixels are inside the hexagon (does not have to be the regular-shaped figure shown above).
C) Change the positions of the vertices, until you find an optimum fit (or until you get tired).
Step (C) is, of course, the hardest one. Plus, if your sprite needs more vertices, you may need to start out with an octagon/n-gon instead.
I'm having a little problem with figuring something out (Obviously).
I'm creating a 2D Top-down mmorpg, and in this game I wish the player to move around a tiled map similar to the way the game Pokemon worked, if anyone has ever played it.
If you have not, picture this: I need to load various areas, constructing them from tiles which contain an image and a location (x, y) and objects (players, items) but the player can only see a portion of it at a time, namely a 20 by 15 tile-wide area, which can be 100s of tiles tall/wide. I want the "camera" to follow the player, keeping him in the center, unless the player reaches the edge of the loaded area.
I don't need code necessarily, just a design plan. I have no idea how to go about this kind of thing.
I was thinking of possibly splitting up the entire loaded area into 10x10 tile pieces, called "Blocks" and loading them, but I'm still not sure how to load pieces off screen and only show them when the player is in range.
The picture should describe it:
Any ideas?
My solution:
The way I solved this problem was through the wonderful world of JScrollPanes and JPanels.
I added a 3x3 block of JPanels inside of a JScrollPane, added a couple scrolling and "goto" methods for centering/moving the JScrollPane around, and voila, I had my camera.
While the answer I chose was a little more generic to people wanting to do 2d camera stuff, the way I did it actually helped me visualize what I was doing a little better since I actually had a physical "Camera" (JScrollPane) to move around my "World" (3x3 Grid of JPanels)
Just thought I would post this here in case anyone was googling for an answer and this came up. :)
For a 2D game, it's quite easy to figure out which tiles fall within a view rectangle, if the tiles are rectangular. Basically, picture a "viewport" rectangle inside the larger world rectangle. By dividing the view offsets by the tile sizes you can easily determine the starting tile, and then just render the tiles in that fit inside the view.
First off, you're working in three coordinate systems: view, world, and map. The view coordinates are essentially mouse offsets from the upper left corner of the view. World coordinates are pixels distances from the upper left corner of tile 0, 0. I'm assuming your world starts in the upper left corner. And map cooridnates are x, y indices into the map array.
You'll need to convert between these in order to do "fancy" things like scrolling, figuring out which tile is under the mouse, and drawing world objects at the correct coordinates in the view. So, you'll need some functions to convert between these systems:
// I haven't touched Java in years, but JavaScript should be easy enough to convey the point
var TileWidth = 40,
TileHeight = 40;
function View() {
this.viewOrigin = [0, 0]; // scroll offset
this.viewSize = [600, 400];
this.map = null;
this.worldSize = [0, 0];
}
View.prototype.viewToWorld = function(v, w) {
w[0] = v[0] + this.viewOrigin[0];
w[1] = v[1] + this.viewOrigin[1];
};
View.prototype.worldToMap = function(w, m) {
m[0] = Math.floor(w[0] / TileWidth);
m[1] = Math.floor(w[1] / TileHeight);
}
View.prototype.mapToWorld = function(m, w) {
w[0] = m[0] * TileWidth;
w[1] = m[1] * TileHeight;
};
View.prototype.worldToView = function(w, v) {
v[0] = w[0] - this.viewOrigin[0];
v[1] = w[1] - this.viewOrigin[1];
}
Armed with these functions we can now render the visible portion of the map...
View.prototype.draw = function() {
var mapStartPos = [0, 0],
worldStartPos = [0, 0],
viewStartPos = [0, 0];
mx, my, // map coordinates of current tile
vx, vy; // view coordinates of current tile
this.worldToMap(this.viewOrigin, mapStartPos); // which tile is closest to the view origin?
this.mapToWorld(mapStartPos, worldStartPos); // round world position to tile corner...
this.worldToView(worldStartPos, viewStartPos); // ... and then convert to view coordinates. this allows per-pixel scrolling
mx = mapStartPos[0];
my = mapStartPos[y];
for (vy = viewStartPos[1]; vy < this.viewSize[1]; vy += TileHeight) {
for (vx = viewStartPos[0]; vx < this.viewSize[0]; vy += TileWidth) {
var tile = this.map.get(mx++, my);
this.drawTile(tile, vx, vy);
}
mx = mapStartPos[0];
my++;
vy += TileHeight;
}
};
That should work. I didn't have time to put together a working demo webpage, but I hope you get the idea.
By changing viewOrigin you can scroll around. To get the world, and map coordinates under the mouse, use the viewToWorld and worldToMap functions.
If you're planning on an isometric view i.e. Diablo, then things get considerably trickier.
Good luck!
The way I would do such a thing is to keep a variable called cameraPosition or something. Then, in the draw method of all objects, use cameraPosition to offset the locations of everything.
For example: A rock is at [100,50], while the camera is at [75,75]. This means the rock should be drawn at [25,-25] (the result of [100,50] - [75,75]).
You might have to tweak this a bit to make it work (for example maybe you have to compensate for window size). Note that you should also do a bit of culling - if something wants to be drawn at [2460,-830], you probably don't want to bother drawing it.
One approach is along the lines of double buffering ( Java Double Buffering ) and blitting ( http://download.oracle.com/javase/tutorial/extra/fullscreen/doublebuf.html ). There is even a design pattern associated with it ( http://www.javalobby.org/forums/thread.jspa?threadID=16867&tstart=0 ).