GAMES LESSON Twenty-four: Making Sprite Transparent
The technique to make the sprite tile transparent is a little bit
complicated, but it works! Basically we just make all the bluish background
from the guy.jpg sprite image transparent and store this in an Image
variable called g2.
The part of the code which filters the bluish background and makes it
transparent is a single method:
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public Image makeClear(){
Image temp=null;
try{
int pixel[] = new int[w*h];
PixelGrabber pg = new PixelGrabber(guy, 0, 0, w, h, pixel, 0, w);
if(pg.grabPixels() &&((pg.status() & ImageObserver.ALLBITS) != 0)){
for(int x = 0; x< w * h; x++){
int r = (pixel[x] & 0x00ff0000)>>16;
int g = (pixel[x] & 0x0000ff00)>>8;
int b = (pixel[x] & 0x000000ff);
//filter for bluish pixels
if(b>50 && g>50){
pixel[x]= (0<<24)|(r<<16)|(g<<8)|b;
}
}
temp=createImage(new MemoryImageSource(w, h, pixel, 0, w));
}
}catch(InterruptedException e) { }
return temp;
}
]]>
The bits which make the image transparent are the first ones in the line
that looks like this:
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pixel[x]= (0<<24)|(r<<16)|(g<<8)|b;
]]>
If the 0 were set to 255 the image would not be transparent at all. Values
between 0 and 255 set the image to different degrees of transparentness. For
instance 50 would be mostly see-through, whereas 200 would be mostly solid.
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import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.awt.image.*;
public class TERR3 extends Applet{
Dimension d;
//brick=0, sky=1, guy=2
int[][] map = {
{ 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1},
{ 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1},
{ 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1},
{ 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,1},
{ 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,1,1,1,1,1,1,1,1},
{ 1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,1,1,1,1,1,1,1},
{ 1,1,1,1,0,0,0,1,1,1,1,2,1,1,1,0,0,0,0,0,0,0,1,1,1,1,1,1},
{ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
};
//28x8
int xguy=11;
int yguy=6;
int xedge = xguy - 5;
int bgx=-100;
int taps;
Image bg, brick, guy;
Image offI;
Image g2;
int w=20;
int h=20;
public void init(){
d = getSize();
offI=createImage(d.width,d.height);
brick = getImage(getDocumentBase(), "brick.jpg");
bg = getImage(getDocumentBase(), "bg.jpg");
guy = getImage(getDocumentBase(), "guy.jpg");
g2 = makeClear();
requestFocus();
this.addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent k) {
if(k.getKeyCode() == KeyEvent.VK_LEFT){
if(taps%2==0) bgx++;
if(xguy>0){
map[yguy][xguy]=1;
xguy--;
if(map[yguy][xguy]==1) map[yguy][xguy]=2;
else{
yguy--;
map[yguy][xguy]=2;
}
}
else{
map[yguy][xguy]=1;
xguy=27;
if(map[yguy][xguy]==1) map[yguy][xguy]=2;
else{
yguy--;
map[yguy][xguy]=2;
}
}
}
else if(k.getKeyCode() == KeyEvent.VK_RIGHT){
if(taps%2==0) bgx--;
map[yguy][xguy]=1;
xguy++;
xguy%=28;
if(map[yguy][xguy]==1) map[yguy][xguy]=2;
else{
yguy--;
map[yguy][xguy]=2;
}
}
if(bgx>0) bgx=0;
if(bgx<-300) bgx=-300;
if(map[yguy+1][xguy]==1){
map[yguy][xguy]=1;
yguy++;
map[yguy][xguy]=2;
}
xedge = xguy-5;
if(xedge<0) xedge=28+xedge;
taps++;
repaint();
}
});
}
public Image makeClear(){
Image temp=null;
try{
int pixel[] = new int[w*h];
PixelGrabber pg = new PixelGrabber(guy, 0, 0, w, h, pixel, 0, w);
if(pg.grabPixels() &&((pg.status() & ImageObserver.ALLBITS) != 0)){
for(int x = 0; x< w * h; x++){
int r = (pixel[x] & 0x00ff0000)>>16;
int g = (pixel[x] & 0x0000ff00)>>8;
int b = (pixel[x] & 0x000000ff);
if(b>50 && g>50){
pixel[x]= (0<<24)|(r<<16)|(g<<8)|b;
}
}
temp=createImage(new MemoryImageSource(w, h, pixel, 0, w));
}
}catch(InterruptedException e) { }
return temp;
}
public void update(Graphics g){
paint(g);
}
public void paint(Graphics g){
Graphics offG = offI.getGraphics();
offG.setColor(Color.black);
offG.drawImage(bg, bgx, 0, this);
int hori=0;
for(int y=0; y<map.length; y++)
for(int x=xedge; x<xedge+11; x++){
if(map[y][x%28] == 0)
offG.drawImage(brick,20*hori,10+20*y,this);
else if(map[y][x%28] == 2)
offG.drawImage(g2,20*hori,10+20*y,this);
hori++;
hori%=11;
}
g.drawImage(offI, 0, 0, this);
}
}
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