This is the sixth part of Egretia Engine tutorial, showing how to build a space shooter game!

Part 1 https://bit.ly/32xy7r3

Part 2 https://bit.ly/2CV2CfC

Part 3 https://bit.ly/39uicLD

Part 4 https://bit.ly/3jJui8p

Part 5 https://bit.ly/31boR9Q

Demonstration

>Lasers

public dx:number;

public dy:number; // Offset value based on player coordinates

public static fi:number = 0 ; // animation frames of laser

//Type

case 10:

//build a picture frame

this.im=Main.createBitmapByName(“pzd4”+ZD.fi+”_png”);

/insert a picture after every shooting

ZD.fi++;

if(ZD.fi >= 10) ZD.fi = 0;

this.addChild(this.im);

//shoot once every pass of main loop, the distance is 80

this.vy = -80; //-80 upwards

this.vx = 0 ;

this.dx = this.dy = 0 ;

this.n = 0;

break;

update()：

//the special one will be scheduled in advance and automatically executed. The “return” will show up when it finishes.

if(this.id == 10){

//the distances between planes and them

this.dx +=this.vx;

this.dy +=this.vy;

//offset value：base value+offset

// coordinates of laser is base coordinates and changes

this.x = this.game.player.x + this.dx;

this.y = this.game.player.y + this.dy;

// test whether it’s off-screen

if(this.y < -100 ){

this.vis = false;

}

return;

}

>Tracking bullet

Demonstration

Version:1.0 StartHTML:000000275 EndHTML:000053955 StartFragment:000021508 EndFragment:000053873 StartSelection:000021508 EndSelection:000053869 SourceURL:https://medium.com/egretia/create-a-space-shooter-game-egretia-engine-tutorial-for-beginners-part-6-a93d80fc08de Create A Space Shooter Game | Egretia Engine Tutorial For Beginners Part 6 | by Egretia Io | Egretia | Aug, 2020 | Medium

1）NPC：

NPCManager

//obtain NPC

public getNPC():NPC{

//length>0,NPC exists; if no, bounce off

if(this.nm.length > 0 ){

//if there is npc, choose one randomly

let npc = this.nm[Math.floor(Math.random()* this.nm.length)]

// decide whether NPC stays in the screen or not

if(npc.x > 0 && npc.x < 480 && npc.y > 0 && npc.y < 800){

return npc;

}

}

//no findings, null

return null;

}

2）calculate the angle to hit NPC
3）update the angle

Apply
public npc:NPC; //the target

/track the bullet

case 20:

this.im = Main.createBitmapByName(“pzd1_3_png”);

this.npc = null;

break;

update()

// the special one will be scheduled in advance and automatically executed. The “return” will show up when it finishes.

if(this.id == 20){

let bn = 0 ; //target angle: upward

if(this.npc == null){

this.npc = this.game.nm.getNPC();

}else{

bn = Math.atan2(this.npc.x -this.x,this.y-this.npc.y);

// This angle is in radians, which will be converted into angle values

bn = bn * 180/ Math.PI;

}

//N angle limit: -180°~180°

while(this.n <= -180)

this.n += 360;

while(this.n > 180)

this.n -= 360;

//if the angle difference is below 5, the two angles are approximately identical

if(Math.abs(this.n — bn) < ZD.VN){

this.n = bn;

}else{

//

if(this.n < bn){

if(this.n < bn — 180)

this.n -= ZD.VN;

else

this.n += ZD.VN;

}else{

if(this.n > bn + 180)

this.n += ZD.VN;

else

this.n -= ZD.VN;

}

}

// convert into angle values

// refresh the speed and angle

this.vx = this.v * Math.sin(this.n * Math.PI / 180);

this.vy= -this.v * Math.cos(this.n * Math.PI / 180);

this.im.rotation = this.n;

this.x +=this.vx;

this.y +=this.vy;

//test the border

if(this.x < -100 || this.x > 580 || this.y < -100 || this.y > 900){

this.vis = false;

}

return;

}

while(this.n <= -180)

this.n += 360;

while(this.n > 180)

this.n -=360;

//track the bullet

this.t++;

if(this.t >= 10){

this.game.zm.create(20,this.x,this.y,15,135,this.game);

this.game.zm.create(20,this.x,this.y,15,-135,this.game);

this.game.zm.create(20,this.x,this.y,15,45,this.game);

this.game.zm.create(20,this.x,this.y,15,-45,this.game);

this.t = 0 ;

}

> The cases of players

0 exit the game
1 playing the game
10 win the game and wait
11 win the game and exit

switch(this.m){

case 0 :

this.y -=this.v;

if(this.y <= 400){

this.m =1;

this.t = 0 ;

}

break;

case 1 :

this.fire();

this.movePlayer();

break;

case 10:

this.t++;

if(this.t >= 20){

this.t = 0;

this.m = 11;

}

break;

case 11:

this.y -=this.vy;

this.vy +=3;

if(this.y < -200){

// the switch of winning the game

}

break;

}

MovePlayer

public movePlayer(){

if(this.isDown == true ){

let a = this.ny — this.oy;

let b = this.nx — this.ox;

let c = Math.sqrt(a*a + b*b);

if( c > this.v){

this.vx = this.v*b/c;

this.vy = this.v*a/c;

this.ox += this.vx;

this.oy += this.vy;

}else{

this.vx = b;

this.vy = a;

this.ox = this.nx;

this.oy = this.ny;

}

// plane will set off at the speed

this.x +=this.vx ;

this.y +=this.vy ;

//test the border

if(this.x < 0)

this.x = 0;

else if(this.x > 480)

this.x = 480;

if(this.y < 0)

this.y = 0;

else if(this.y > 800)

this.y = 800;

}

else{

this.vx = 0;

}

if(this.vx < 0 ){

//fly towards the left side：

if(this.fi > -2)

this.fi — ;

}else if(this.vx > 0)

{

if(this.fi < 2)

this.fi++;

}

else{

this.fi = 0 ;

}

this.resetFI();

}

>public isHit(x:number , y:number):boolean{}

public isHit(x:number , y:number):boolean{

// this.x this.y is the center of a circle， 60 is radius

// Formula of the distance between two points

if(this.bhT > 0 ){

if((this.x -x )*(this.x -x ) + (this.y -y )*(this.y — y ) < 60*60){

return true;

}

return false;

}

if(this.m !=1)

return false;

if(Math.abs(this.x — x) < 20 && Math.abs(this.y -y )<20){

//death of players

return true;

}

return false;

}

add

public dead(){

for(let i = 0 ; i < 10 ; i++){ //ring

let dn =Math.random()*Math.PI * 2;

for(let j = 0 ; j < 15 ; j ++) //the bombs of each ring

{

this.game.tm.create(0,

this.x + (i+1)*30* Math.sin(dn+Math.PI*2*j/15),

this.y + (i+1)*30* Math.cos(dn+Math.PI*2*j/15),

i,Math.random() * 10 +5,this.game);

}

}

this.x = 240;

this.y = 1000;

this.m = 0 ;

this.t = 0;

}

> Players’ Shield

public bh:egret.Bitmap; // shield photo
public bhT:number; // shield timer: last 3 seconds
this.bh.anchorOffsetX = this.bh.width/2;
this.bh.anchorOffsetY =this.bh.height/2;
this.addChild(this.bh);
this.bh.scaleX = this.bh.scaleY = 0.5;
this.bhT = 60; // three seconds for 60 passes of main loop

Update;
//shield effective time>0. Visible = false when it comes to 0

if(this.bhT > 0 ){

this.bhT — ;

if(this.bhT <=0){

this.bh.visible = false;

}

}

NZDManager

if(this.game.player.isHit(one.x , one.y) ==true ){

one.vis = false;

if(this.game.player.m == 1 && this.game.player.bhT <= 0 ){

this.game.player.dead();

}

}

this.bhT = 60;
this.bh.visible = true;

> Win the game and Game level switch

BOSS0

public dead(){

for(let i = 0 ; i < 10 ; i++){ //ring

let dn =Math.random()*Math.PI * 2;

for(let j = 0 ; j < 15 ; j ++) //the number of bombs of each ring

{

this.nm.game.tm.create(0,

this.x + (i+1)*30* Math.sin(dn+Math.PI*2*j/15),

this.y + (i+1)*30* Math.cos(dn+Math.PI*2*j/15),

i,Math.random() * 10 +5,this.nm.game);

}

}

this.nm.game.player.win();

}

//pass

public win(){

this.t = 0 ;

this.m = 10; //Player will fly off the screen after victory

}

2）Level switch
Maingame:

apply public level:number; // to figure out the current level
construct：this.level = 0;

Maingame:

public reset(level:number)

{

this.level = level;

this.player.reset();

this.bg.reset();

this.nm.reset();

}

BG

public reset(){

switch(this.game.level){

case 0:

for(let i = 0 ; i < 2; i ++){

this.bg[i].texture = RES.getRes(“bg11_jpg”);

}

break;

case 1:

for(let i = 0 ; i < 2; i ++){

this.bg[i].texture = RES.getRes(“bg31_jpg”);

}

break;

}

}

NPCManager

//clean out

public reset(){

//the total length. To find out all the bullets by circulation

for(let i = 0 ; i < this.nm.length ; i++){

//find out every bullet

let one = this.nm[i];

this.removeChild(one);

this.nm.splice(i ,1);

i — ;

}

this.t =0;

this.cID = 0;

}

Player

public dead(){

for(let i = 0 ; i < 10 ; i++){ //rings

let dn =Math.random()*Math.PI * 2;

for(let j = 0 ; j < 15 ; j ++) //the number of bombs for each ring

{

this.game.tm.create(0,

this.x + (i+1)*30* Math.sin(dn+Math.PI*2*j/15),

this.y + (i+1)*30* Math.cos(dn+Math.PI*2*j/15),

i,Math.random() * 10 +5,this.game);

}

}

this.x = 240;

this.y = 700;

this.m = 0 ;

this.t = 0;

this.bhT = 60;

this.bh.visible = true;

}

public reset(){

this.isDown = false;

this.x = 240;this.y = 1000;

this.m = this.t = 0;

this.bhT = 60; //it will take 3 seconds for 60 passes of main loop

}

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