In this episode we will add the explosion animations for the Invaders. I did mention we’d add in the scoring as well but on reflection I’m going to leave that for a later episode because I do not want to put two different items in this article and scoring would be better suited when we have more game elements.
As usual the full code is below (expand and copy as required).
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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 // 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 // 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 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]; // 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 // 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); } void loop() { Physics(); UpdateDisplay(); } void Physics() { AlienControl(); PlayerControl(); MissileControl(); CheckCollisions(); } 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(); } 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() { display.clearDisplay(); 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); 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 the 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; } } } |
The length of an explosion
The amount of time the explosion graphic is on screen is determined by this constant:
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#define EXPLOSION_GFX_TIME 7 // How long an ExplosionGfx remains on screen before dissapearing |
The higher the number the longer the graphic remains on screen.
A new object status
An object’s status could be either ACTIVE or DESTROYED but now (if you look below) we have introduced a new status called EXPLODING
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#define ACTIVE 0 #define EXPLODING 1 #define DESTROYED 2 |
This code allows the UpdateDisplay routine to know when it should be displaying the explosion graphic for that object rather than its normal graphic.
The explosion graphic
The definition for the explosion starts at line 112 and will not be discussed further as graphics were covered in a earlier episode.
The Alien’s structure
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struct AlienStruct { GameObjectStruct Ord; unsigned char ExplosionGfxCounter; // how long we want the ExplosionGfx to last }; |
We have added the variable to time how long the explosion remains on this screen for this Alien. Initially when it is hit it will be filled with the EXPLOSION_GFX_TIME constant value and then decremented for every time the code loops round its main loop. We’ll discuss this further shortly.
Missile Collisions
Previously within the routine MissileAndAlienCollisions we had a line that read
Alien[across][down].Ord.Status=DESTROYED;
Now (on line 288) we have changed this to
Alien[across][down].Ord.Status=EXPLODING;
To indicate that this Alien is exploding – not yet destroyed.
Displaying the explosions
In the UpdateDisplay routine we have added these lines at line 375
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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; } } |
This code is executed if the Invader is not active (decided on line 354 – not shown here but in main code at the start of the article). Looking above we can see that if the Invader has the status of EXPLODING then we go on to decrement the explosion counter. Then we decide whether to display the explosion or mark the Invader as destroyed. If the explosion counter (ExplosionGfxCounter) is more than 0 we display the explosion else we mark the Invader as DESTROYED and then nothing else will happen for this Invader for this wave of Invaders.
Invader Initialisation
We need to add a couple of lines to the initialisation code:
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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 the 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; } } } |
Lines 411-412 are the new lines showing that we are setting the Invader Status to ACTIVE (this should have been included prior to this episode to be fair) and we also set the explosion counter to its starting point ready for an explosion to happen.
That’s it for now, next time we’ll look at adding the mothership that goes across the screen.
Enjoy and Learn 🙂