In this episode we add the Mother-ship (Mystery-ship) that goes across the top of the screen. Also available as a video:
In this implementation it is random, in the real arcade game it appears approximately every 25 seconds or so. The scoring for it is also random, either 50,100,150 or 300 points. In the real arcade game it appears random but in fact it can be influenced by the players actions.
The Code
Full code that you can just paste in is below.
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#include <Adafruit_SSD1306.h> #include <Adafruit_GFX.h> // DISPLAY SETTINGS #define OLED_ADDRESS 0x3C #define SCREEN_WIDTH 128 #define SCREEN_HEIGHT 64 // Input settings #define FIRE_BUT 6 #define RIGHT_BUT 5 #define LEFT_BUT 4 // Mothership #define MOTHERSHIP_HEIGHT 4 #define MOTHERSHIP_WIDTH 16 #define MOTHERSHIP_SPEED 2 #define MOTHERSHIP_SPAWN_CHANCE 250 //HIGHER IS LESS CHANCE OF SPAWN #define DISPLAY_MOTHERSHIP_BONUS_TIME 20 // how long bonus stays on screen for displaying mothership // Alien Settings #define NUM_ALIEN_COLUMNS 7 #define NUM_ALIEN_ROWS 3 #define X_START_OFFSET 6 #define SPACE_BETWEEN_ALIEN_COLUMNS 5 #define LARGEST_ALIEN_WIDTH 11 #define SPACE_BETWEEN_ROWS 9 #define INVADERS_DROP_BY 4 // pixel amount that invaders move down by #define INVADERS_SPEED 12 // speed of movement, lower=faster. #define INVADER_HEIGHT 8 #define EXPLOSION_GFX_TIME 7 // How long an ExplosionGfx remains on screen before dissapearing #define INVADERS_Y_START MOTHERSHIP_HEIGHT-1 // Player settingsc #define TANKGFX_WIDTH 13 #define TANKGFX_HEIGHT 8 #define PLAYER_X_MOVE_AMOUNT 2 #define PLAYER_Y_START 56 #define PLAYER_X_START 0 #define MISSILE_HEIGHT 4 #define MISSILE_WIDTH 1 #define MISSILE_SPEED 4 // Status of a game object constants #define ACTIVE 0 #define EXPLODING 1 #define DESTROYED 2 // graphics // aliens const unsigned char MotherShipGfx [] PROGMEM = { B00111111,B11111100, B01101101,B10110110, B11111111,B11111111, B00111001,B10011100 }; const unsigned char InvaderTopGfx [] PROGMEM = { B00011000, B00111100, B01111110, B11011011, B11111111, B00100100, B01011010, B10100101 }; const unsigned char InvaderTopGfx2 [] PROGMEM = { B00011000, B00111100, B01111110, B11011011, B11111111, B01011010, B10000001, B01000010 }; const unsigned char PROGMEM InvaderMiddleGfx []= { B00100000,B10000000, B00010001,B00000000, B00111111,B10000000, B01101110,B11000000, B11111111,B11100000, B10111111,B10100000, B10100000,B10100000, B00011011,B00000000 }; const unsigned char PROGMEM InvaderMiddleGfx2 [] = { B00100000,B10000000, B00010001,B00000000, B10111111,B10100000, B10101110,B10100000, B11111111,B11100000, B00111111,B10000000, B00100000,B10000000, B01000000,B01000000 }; const unsigned char PROGMEM InvaderBottomGfx [] = { B00001111,B00000000, B01111111,B11100000, B11111111,B11110000, B11100110,B01110000, B11111111,B11110000, B00111001,B11000000, B01100110,B01100000, B00110000,B11000000 }; const unsigned char PROGMEM InvaderBottomGfx2 [] = { B00001111,B00000000, B01111111,B11100000, B11111111,B11110000, B11100110,B01110000, B11111111,B11110000, B00111001,B11000000, B01000110,B00100000, B10000000,B00010000 }; static const unsigned char PROGMEM ExplosionGfx [] = { B00001000,B10000000, B01000101,B00010000, B00100000,B00100000, B00010000,B01000000, B11000000,B00011000, B00010000,B01000000, B00100101,B00100000, B01001000,B10010000 }; // Player grafix const unsigned char PROGMEM TankGfx [] = { B00000010,B00000000, B00000111,B00000000, B00000111,B00000000, B01111111,B11110000, B11111111,B11111000, B11111111,B11111000, B11111111,B11111000, B11111111,B11111000, }; static const unsigned char PROGMEM MissileGfx [] = { B10000000, B10000000, B10000000, B10000000 }; // Game structures struct GameObjectStruct { // base object which most other objects will include signed int X; signed int Y; unsigned char Status; //0 active, 1 exploding, 2 destroyed }; struct AlienStruct { GameObjectStruct Ord; unsigned char ExplosionGfxCounter; // how long we want the ExplosionGfx to last }; struct PlayerStruct { GameObjectStruct Ord; }; // general global variables Adafruit_SSD1306 display(1); //alien global vars //The array of aliens across the screen AlienStruct Alien[NUM_ALIEN_COLUMNS][NUM_ALIEN_ROWS]; AlienStruct MotherShip; // widths of aliens // as aliens are the same type per row we do not need to store their graphic width per alien in the structure above // that would take a byte per alien rather than just three entries here, 1 per row, saving significnt memory byte AlienWidth[]={8,11,12}; // top, middle ,bottom widths char AlienXMoveAmount=2; signed char InvadersMoveCounter; // counts down, when 0 move invaders, set according to how many aliens on screen bool AnimationFrame=false; // two frames of animation, if true show one if false show the other // Mothership signed char MotherShipSpeed; unsigned int MotherShipBonus; signed int MotherShipBonusXPos; // pos to display bonus at unsigned char MotherShipBonusCounter; // how long bonus amount left on screen // Player global variables PlayerStruct Player; GameObjectStruct Missile; void setup() { display.begin(SSD1306_SWITCHCAPVCC,OLED_ADDRESS); InitAliens(0); InitPlayer(); pinMode(RIGHT_BUT, INPUT_PULLUP); pinMode(LEFT_BUT, INPUT_PULLUP); pinMode(FIRE_BUT, INPUT_PULLUP); display.setTextSize(1); display.setTextColor(WHITE); } void loop() { Physics(); UpdateDisplay(); } void Physics() { AlienControl(); MotherShipPhysics(); PlayerControl(); MissileControl(); CheckCollisions(); } void MotherShipPhysics() { if(MotherShip.Ord.Status==ACTIVE) {// spawned, move it MotherShip.Ord.X+=MotherShipSpeed; if(MotherShipSpeed>0) // going left to right , check if off right hand side { if(MotherShip.Ord.X>=SCREEN_WIDTH) { MotherShip.Ord.Status=DESTROYED; } } else // going right to left , check if off left hand side { if(MotherShip.Ord.X+MOTHERSHIP_WIDTH<0) { MotherShip.Ord.Status=DESTROYED; } } } else { // try to spawn mothership if(random(MOTHERSHIP_SPAWN_CHANCE)==1) { // Spawn a mother ship, starts just off screen at top MotherShip.Ord.Status=ACTIVE; // need to set direction if(random(2)==1) // values between 0 and 1 { MotherShip.Ord.X=SCREEN_WIDTH; MotherShipSpeed=-MOTHERSHIP_SPEED; // if we go in here swaps to right to left } else { MotherShip.Ord.X=-MOTHERSHIP_WIDTH; MotherShipSpeed=MOTHERSHIP_SPEED; // set to go left ot right } } } } void PlayerControl() { // user input checks if((digitalRead(RIGHT_BUT)==0)&(Player.Ord.X+TANKGFX_WIDTH<SCREEN_WIDTH)) Player.Ord.X+=PLAYER_X_MOVE_AMOUNT; if((digitalRead(LEFT_BUT)==0)&(Player.Ord.X>0)) Player.Ord.X-=PLAYER_X_MOVE_AMOUNT; if((digitalRead(FIRE_BUT)==0)&(Missile.Status!=ACTIVE)) { Missile.X=Player.Ord.X+(TANKGFX_WIDTH/2); Missile.Y=PLAYER_Y_START; Missile.Status=ACTIVE; } } void MissileControl() { if(Missile.Status==ACTIVE) { Missile.Y-=MISSILE_SPEED; if(Missile.Y+MISSILE_HEIGHT<0) // If off top of screen destroy so can be used again Missile.Status=DESTROYED; } } void AlienControl() { if((InvadersMoveCounter--)<0) { bool Dropped=false; if((RightMostPos()+AlienXMoveAmount>=SCREEN_WIDTH) |(LeftMostPos()+AlienXMoveAmount<0)) // at edge of screen { AlienXMoveAmount=-AlienXMoveAmount; // reverse direction Dropped=true; // and indicate we are dropping } // update the alien postions for(int Across=0;Across<NUM_ALIEN_COLUMNS;Across++) { for(int Down=0;Down<3;Down++) { if(Alien[Across][Down].Ord.Status==ACTIVE) { if(Dropped==false) Alien[Across][Down].Ord.X+=AlienXMoveAmount; else Alien[Across][Down].Ord.Y+=INVADERS_DROP_BY; } } } InvadersMoveCounter=INVADERS_SPEED; AnimationFrame=!AnimationFrame; ///swap to other frame } } void CheckCollisions() { MissileAndAlienCollisions(); MotherShipCollisions(); } void MotherShipCollisions() { if((Missile.Status==ACTIVE)&(MotherShip.Ord.Status==ACTIVE)) { if(Collision(Missile,MISSILE_WIDTH,MISSILE_HEIGHT,MotherShip.Ord,MOTHERSHIP_WIDTH,MOTHERSHIP_HEIGHT)) { MotherShip.Ord.Status=EXPLODING; MotherShip.ExplosionGfxCounter=EXPLOSION_GFX_TIME; Missile.Status=DESTROYED; // generate the score for the mothership hit, note in the real arcade space invaders the score was not random but // just appeared so, a player could infulence its value with clever play, but we'll keep it a little simpler MotherShipBonus=random(4); // a random number between 0 and 3 switch(MotherShipBonus) { case 0:MotherShipBonus=50;break; case 1:MotherShipBonus=100;break; case 2:MotherShipBonus=150;break; case 3:MotherShipBonus=300;break; } MotherShipBonusXPos=MotherShip.Ord.X; if(MotherShipBonusXPos>100) // to ensure isn't half off right hand side of screen MotherShipBonusXPos=100; if(MotherShipBonusXPos<0) // to ensure isn't half off right hand side of screen MotherShipBonusXPos=0; MotherShipBonusCounter=DISPLAY_MOTHERSHIP_BONUS_TIME; } } } void MissileAndAlienCollisions() { for(int across=0;across<NUM_ALIEN_COLUMNS;across++) { for(int down=0;down<NUM_ALIEN_ROWS;down++) { if(Alien[across][down].Ord.Status==ACTIVE) { if(Missile.Status==ACTIVE) { if(Collision(Missile,MISSILE_WIDTH,MISSILE_HEIGHT,Alien[across][down].Ord,AlienWidth[down],INVADER_HEIGHT)) { // missile hit Alien[across][down].Ord.Status=EXPLODING; Missile.Status=DESTROYED; } } } } } } bool Collision(GameObjectStruct Obj1,unsigned char Width1,unsigned char Height1,GameObjectStruct Obj2,unsigned char Width2,unsigned char Height2) { return ((Obj1.X+Width1>Obj2.X)&(Obj1.X<Obj2.X+Width2)&(Obj1.Y+Height1>Obj2.Y)&(Obj1.Y<Obj2.Y+Height2)); } int RightMostPos() { //returns x pos of right most alien int Across=NUM_ALIEN_COLUMNS-1; int Down; int Largest=0; int RightPos; while(Across>=0){ Down=0; while(Down<NUM_ALIEN_ROWS){ if(Alien[Across][Down].Ord.Status==ACTIVE) { // different aliens have different widths, add to x pos to get rightpos RightPos= Alien[Across][Down].Ord.X+AlienWidth[Down]; if(RightPos>Largest) Largest=RightPos; } Down++; } if(Largest>0) // we have found largest for this coloum return Largest; Across--; } return 0; // should never get this far } int LeftMostPos() { //returns x pos of left most alien int Across=0; int Down; int Smallest=SCREEN_WIDTH*2; while(Across<NUM_ALIEN_COLUMNS){ Down=0; while(Down<3){ if(Alien[Across][Down].Ord.Status==ACTIVE) if(Alien[Across][Down].Ord.X<Smallest) Smallest=Alien[Across][Down].Ord.X; Down++; } if(Smallest<SCREEN_WIDTH*2) // we have found smalest for this coloum return Smallest; Across++; } return 0; // should nevr get this far } void UpdateDisplay() { int i; display.clearDisplay(); // Mothership bonus display if required if(MotherShipBonusCounter>0) { // mothership bonus display.setCursor(MotherShipBonusXPos,0); display.print(MotherShipBonus); MotherShipBonusCounter--; } //Invaders for(int across=0;across<NUM_ALIEN_COLUMNS;across++) { for(int down=0;down<NUM_ALIEN_ROWS;down++) { if(Alien[across][down].Ord.Status==ACTIVE){ switch(down) { case 0: if(AnimationFrame) display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, InvaderTopGfx, AlienWidth[down],INVADER_HEIGHT,WHITE); else display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, InvaderTopGfx2, AlienWidth[down],INVADER_HEIGHT,WHITE); break; case 1: if(AnimationFrame) display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, InvaderMiddleGfx, AlienWidth[down],INVADER_HEIGHT,WHITE); else display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, InvaderMiddleGfx2, AlienWidth[down],INVADER_HEIGHT,WHITE); break; default: if(AnimationFrame) display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, InvaderBottomGfx, AlienWidth[down],INVADER_HEIGHT,WHITE); else display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, InvaderBottomGfx2, AlienWidth[down],INVADER_HEIGHT,WHITE); } } else { if(Alien[across][down].Ord.Status==EXPLODING){ Alien[across][down].ExplosionGfxCounter--; if(Alien[across][down].ExplosionGfxCounter>0) { display.drawBitmap(Alien[across][down].Ord.X, Alien[across][down].Ord.Y, ExplosionGfx, 13, 8,WHITE); } else Alien[across][down].Ord.Status=DESTROYED; } } } } // player display.drawBitmap(Player.Ord.X, Player.Ord.Y, TankGfx, TANKGFX_WIDTH, TANKGFX_HEIGHT,WHITE); //missile if(Missile.Status==ACTIVE) display.drawBitmap(Missile.X, Missile.Y, MissileGfx, MISSILE_WIDTH, MISSILE_HEIGHT,WHITE); // mothership (not bonus if hit) if(MotherShip.Ord.Status==ACTIVE) display.drawBitmap(MotherShip.Ord.X, MotherShip.Ord.Y, MotherShipGfx, MOTHERSHIP_WIDTH, MOTHERSHIP_HEIGHT,WHITE); else { if(MotherShip.Ord.Status==EXPLODING) { for(i=0;i<MOTHERSHIP_WIDTH;i+=2) { display.drawBitmap(MotherShip.Ord.X+i, MotherShip.Ord.Y, ExplosionGfx, random(4)+2, MOTHERSHIP_HEIGHT,WHITE); } MotherShip.ExplosionGfxCounter--; if(MotherShip.ExplosionGfxCounter==0) { MotherShip.Ord.Status=DESTROYED; } } } display.display(); } void InitPlayer() { Player.Ord.Y=PLAYER_Y_START; Player.Ord.X=PLAYER_X_START; Missile.Status=DESTROYED; } void InitAliens(int YStart) { for(int across=0;across<NUM_ALIEN_COLUMNS;across++) { for(int down=0;down<3;down++) { // we add down to centralise tscore he aliens, just happens to be the right value we need per row! // we need to adjust a little as row zero should be 2, row 1 should be 1 and bottom row 0 Alien[across][down].Ord.X=X_START_OFFSET+(across*(LARGEST_ALIEN_WIDTH+SPACE_BETWEEN_ALIEN_COLUMNS))-(AlienWidth[down]/2); Alien[across][down].Ord.Y=YStart+(down*SPACE_BETWEEN_ROWS); Alien[across][down].Ord.Status=ACTIVE; Alien[across][down].ExplosionGfxCounter=EXPLOSION_GFX_TIME; } } MotherShip.Ord.Y=0; MotherShip.Ord.X=-MOTHERSHIP_WIDTH; MotherShip.Ord.Status=DESTROYED; } |
Lines 15-19 define some values for the mystery ship (I’ll call it both mystery and mothership in this article quite freely!).
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// Mothership #define MOTHERSHIP_HEIGHT 4 #define MOTHERSHIP_WIDTH 16 #define MOTHERSHIP_SPEED 2 #define MOTHERSHIP_SPAWN_CHANCE 250 //HIGHER IS LESS CHANCE OF SPAWN #define DISPLAY_MOTHERSHIP_BONUS_TIME 20 // how long bonus stays on screen for displaying mothership |
Lines 15-16 are I hope self explanatory. Line 17 sets the speed that the ship travels across the screen, the higher the faster. It’s basically the number of pixels moved at a time. We then have a value that effects the frequency that the ship appears. The higher the less frequent. Line 19 controls how long the bonus score you got (i.e. 50,100,150,300) stays on screen in the position where the mothership was destroyed. Bigger the number the longer.
Lines 53-58 define the graphics – which we won’t go into as we have covered this in pevious articles.
Line 185 creates a global variable of type AlienStruct to keep track of the ship.
AlienStruct MotherShip;
We also have some other global variables that keep track of various aspects of the mothership, these are at lines 198-202
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// Mothership signed char MotherShipSpeed; unsigned int MotherShipBonus; signed int MotherShipBonusXPos; // pos to display bonus at unsigned char MotherShipBonusCounter; // how long bonus amount left on screen |
MotherShipSpeed has the current speed and direction of the mothership and it takes its value directly from MOTHERSHIP_SPEED defined earlier. If its a positive value then it will be move from left to right, if negative then right to left. MotherShipBonus stores the bonus earned if you hit the mothership. This is displayed where the mothership was destroyed. MotherShipBonusCounter is the counter that starts with the value defined by DISPLAY_MOTHERSHIP_BONUS_TIME and it is decremented and on reaching 0 the bonus score is no longer displayed.
Mother-ship physics
The physics routine has been expanded to handle the mothership:
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void Physics() { AlienControl(); MotherShipPhysics(); PlayerControl(); MissileControl(); CheckCollisions(); } |
It calls MotherShipPhysics(), which is below:
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void MotherShipPhysics() { if(MotherShip.Ord.Status==ACTIVE) {// spawned, move it MotherShip.Ord.X+=MotherShipSpeed; if(MotherShipSpeed>0) // going left to right , check if off right hand side { if(MotherShip.Ord.X>=SCREEN_WIDTH) { MotherShip.Ord.Status=DESTROYED; } } else // going right to left , check if off left hand side { if(MotherShip.Ord.X+MOTHERSHIP_WIDTH<0) { MotherShip.Ord.Status=DESTROYED; } } } else { // try to spawn mothership if(random(MOTHERSHIP_SPAWN_CHANCE)==1) { // Spawn a mother ship, starts just off screen at top MotherShip.Ord.Status=ACTIVE; // need to set direction if(random(2)==1) // values between 0 and 1 { MotherShip.Ord.X=SCREEN_WIDTH; MotherShipSpeed=-MOTHERSHIP_SPEED; // if we go in here swaps to right to left } else { MotherShip.Ord.X=-MOTHERSHIP_WIDTH; MotherShipSpeed=MOTHERSHIP_SPEED; // set to go left ot right } } } } |
Looking at the code, if the ship is active we handle moving it across the screen and check if it goes off the screen, destroying it (without a score being earned) if it does.
If not active then we randomly decide if a ship should appear, if one should we then set a 50/50 chance as to which direction it should travel (setting its position and speed accordingly).
Mother-ship collisions
The check collisions routine at line 333 has also been expanded to call MotherShipCollisions().
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void CheckCollisions() { MissileAndAlienCollisions(); MotherShipCollisions(); } |
MotherShipCollisions()
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void MotherShipCollisions() { if((Missile.Status==ACTIVE)&(MotherShip.Ord.Status==ACTIVE)) { if(Collision(Missile,MISSILE_WIDTH,MISSILE_HEIGHT,MotherShip.Ord,MOTHERSHIP_WIDTH,MOTHERSHIP_HEIGHT)) { MotherShip.Ord.Status=EXPLODING; MotherShip.ExplosionGfxCounter=EXPLOSION_GFX_TIME; Missile.Status=DESTROYED; // generate the score for the mothership hit, note in the real arcade space invaders the score was not random but // just appeared so, a player could infulence its value with clever play, but we'll keep it a little simpler MotherShipBonus=random(4); // a random number between 0 and 3 switch(MotherShipBonus) { case 0:MotherShipBonus=50;break; case 1:MotherShipBonus=100;break; case 2:MotherShipBonus=150;break; case 3:MotherShipBonus=300;break; } MotherShipBonusXPos=MotherShip.Ord.X; if(MotherShipBonusXPos>100) // to ensure isn't half off right hand side of screen MotherShipBonusXPos=100; if(MotherShipBonusXPos<0) // to ensure isn't half off right hand side of screen MotherShipBonusXPos=0; MotherShipBonusCounter=DISPLAY_MOTHERSHIP_BONUS_TIME; } } } |
In this routine if the players missile is active and the mothership is active then we check for a collision between the two. If we get a collision then we choose a random bonus and set the position that this will be shown on screen and set the counter for the duration that its shown on screen.
Displaying the mothership and bonus score
The UpdateDisplay() routine now also displays any bonus earned as long as the bonus display counter is above 0. Lines 448 to 455 handle this:
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// Mothership bonus display if required if(MotherShipBonusCounter>0) { // mothership bonus display.setCursor(MotherShipBonusXPos,0); display.print(MotherShipBonus); MotherShipBonusCounter--; } |
Lines 502-517 display the actual ship:
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// mothership (not bonus if hit) if(MotherShip.Ord.Status==ACTIVE) display.drawBitmap(MotherShip.Ord.X, MotherShip.Ord.Y, MotherShipGfx, MOTHERSHIP_WIDTH, MOTHERSHIP_HEIGHT,WHITE); else { if(MotherShip.Ord.Status==EXPLODING) { for(i=0;i<MOTHERSHIP_WIDTH;i+=2) { display.drawBitmap(MotherShip.Ord.X+i, MotherShip.Ord.Y, ExplosionGfx, random(4)+2, MOTHERSHIP_HEIGHT,WHITE); } MotherShip.ExplosionGfxCounter--; if(MotherShip.ExplosionGfxCounter==0) { MotherShip.Ord.Status=DESTROYED; } } } |
If Active we just display it else we check if its currently exploding, if so we draw the explosion graphic at random widths where the ship was for the amount of time that explosions are supposed to appear on screen (discussed in an earlier article).
Lines 541-543 initialise the mothership to ensure sensible values
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MotherShip.Ord.Y=0; MotherShip.Ord.X=-MOTHERSHIP_WIDTH; MotherShip.Ord.Status=DESTROYED; |
That’s it for this article, next time we’ll look at adding in the scoring and high score capability.
All for now, see you next time 🙂