In this article we look at adding the player bases (defensive structures). Again we are not looking a line by line account, but rather an overview of what’s been done. As always a companion video is available on youtube:
Bases need to be destroyed – The problem with Adafruit_GFX.h
As you probably know these bases need to be destroyed in a bit-by-bit style either by the Invaders or the player shooting into them. But herein lies the problem. Take a look at the definition for the base (or any other graphic)
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static const unsigned char PROGMEM BaseGfx [] = { B00011111,B11111000, B01111111,B11111110, B11111111,B11111111, B11111111,B11111111, B11111111,B11111111, B11111000,B00011111, B11100000,B00000111, B11100000,B00000111 }; |
This uses the compiler directive PROGMEM, this was mentioned in an earlier article on graphics and it allows us to store our data in the Atmel processors (used by Arduino) program memory rather than the usual data memory. This is very important in games on the Arduino due to the very limited data memory available (2Kb). We have 32Kb of program memory and it would be far better to store these large data items in there if we can. And so far that is what we’ve done and no problems. If these bases were not damageable, i.e. never changing we would use this method, but each one on the screen can have bits of it removed when hit and in different ways. With PROGMEM once something is stored in there it cannot be changed by your code, only by re-programming by the usual interface. So we cannot just alter the graphic during run-time.
Choices for destruction
So we could actually store different versions of a destroyed base in PROGMEM and display which ever was appropriate depending on the damage inflicted. However this is a valid method when you have only a few permutations of the graphic. For these bases there will be a wide variety of different damage, far too many to store a different graphic for each possible looking damaged base.
So we have no choice, we have to store the graphic in normal dynamic RAM (all 2K of it!). In this way we can alter whatever parts of the graphic are destroyed. We will still store our original base graphic in program memory (unchanging) and just make new copies of it for each base at the bottom for each new level. When I was developing this part I was unsure if I would have enough memory in RAM but after implementing I did, phew!
Adafruit_GFX
There was another issue though, the Adafruit graphics library we use will only work with graphics stored in program memory by the PROGEM directive. So I had to add a new routine that could display graphics from dynamic memory. This has been forked on GitHub and is also available on this website. More on that later.
The base structure
Below is the new structure for a base
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struct BaseStruct { GameObjectStruct Ord; unsigned char Gfx[16]; }; |
As is usual we use the GameObjectStruct structure to give the item positional information, and then in addition we have some memory reserved for the graphic (16 bytes in total). This is the size of the base graphic just above which is stored in program memory for our code to copy from into this dynamic memory that we can change. The function below handles this task and is called when a new level is started.
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void InitBases() { // Bases need to be re-built! uint8_t TheByte; int Spacing=(SCREEN_WIDTH-(NUM_BASES*BASE_WIDTH))/NUM_BASES; for(int i=0;i<NUM_BASES;i++) { for(int DataIdx=0;DataIdx<BASE_HEIGHT*BASE_WIDTH_IN_BYTES;DataIdx++) { TheByte = pgm_read_byte(BaseGfx + DataIdx); Base[i].Gfx[DataIdx]=TheByte; } Base[i].Ord.X=(i*Spacing)+(i*BASE_WIDTH)+(Spacing/2); Base[i].Ord.Y=BASE_Y; Base[i].Ord.Status=ACTIVE; } } |
We can see we have a #define NUM_BASES for the number of bases on screen. The code then spaces them out evenly on the screen (the “i” loop) and the “DataIdx” loop copies the graphics data in program memory into the Gfx array in dynamic memory.
Base Collisions
This is quite a complex piece of code as we have to destroy bits of a base at pixel level and those pixels are stored in various bytes in the base graphics. It is only complex because of this pixel level destruction on a graphic whose pixels are part of a byte. Apart from this it is relativly straight forward. The three routines that handle collisions are
BombAndBasesCollision, MissileAndBasesCollisions and AlienAndBaseCollisions
BombAndBasesCollision, MissileAndBasesCollisions
These are virtually identical apart from one destroys the base from top to bottom and the other from the bottom up. Which ever it is the routine randomly decides how deep to go (up or down) and how much side-wards damage is done on the way down (again randomly). In the real arcade this was not so random as it had three slightly different missiles which penetrated to different amounts (and also travelled at different speeds). But I have not implemented it this way in this version, but it plays virtually the same.
AlienAndBaseCollisions
This handles collisions between Invaders and the bases. As an Invader collides bits of a base are removed.
The altered AdaFruit_Gfx
It is very important that before you put the new code on your Arduino that you add the altered AdaFruit library. Otherwise you will probably forget and wonder why things don’t quite look right. The easiest way to do this is to replace the file in your library folder with the new one linked just below.
To do this open up your Arduino folder, the one where your programs are stored (on windows it will probably be called Arduino and be in the MyDocuments folder). Within this you will see a “libraries” folder and within this (provided you have been following these tutorials) will be the folder Adafruit-GFX-Library-master. Delete this and then extract the contents of the zip folder just above into the libraries folder.
If you haven’t been following this series and you have never installed the Adafruit-GFX-Library-master library then ensure you first do so by looking at the guide to hooking up the 128×64 oled screen used in this project, see here. Then come back to this page.
The Code
Now you are ready to copy and paste the code below into your Invaders project and upload.
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#include <Adafruit_SSD1306.h> #include <Adafruit_GFX.h> #include <EEPROM.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 ALIEN_HEIGHT 8 #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 #define AMOUNT_TO_DROP_BY_PER_LEVEL 4 //NEW How much farther down aliens start per new level #define LEVEL_TO_RESET_TO_START_HEIGHT 4 // EVERY MULTIPLE OF THIS LEVEL THE ALIEN y START POSITION WILL RESET TO TOP #define ALIEN_X_MOVE_AMOUNT 1 //number of pixels moved at start of wave #define CHANCEOFBOMBDROPPING 20 // Higher the number the rarer the bomb drop, #define BOMB_HEIGHT 4 #define BOMB_WIDTH 2 #define MAXBOMBS 3 // Max number of bombs allowed to drop at a time // These two lines are for when bombs collide with the bases #define CHANCE_OF_BOMB_DAMAGE_TO_LEFT_OR_RIGHT 3 // higher more chance #define CHANCE_OF_BOMB_PENETRATING_DOWN 3 // higher more chance // Player settingsc #define TANKGFX_WIDTH 13 #define TANKGFX_HEIGHT 8 #define PLAYER_X_MOVE_AMOUNT 2 #define LIVES 3 //NEW #define PLAYER_EXPLOSION_TIME 10 // How long an ExplosionGfx remains on screen before dissapearing #define PLAYER_Y_START 56 #define PLAYER_X_START 0 #define BASE_WIDTH 16 #define BASE_WIDTH_IN_BYTES 2 #define BASE_HEIGHT 8 #define BASE_Y 46 #define NUM_BASES 4 #define BASE_MARGINS 10 #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 }; static const unsigned char PROGMEM AlienBombGfx [] = { B10000000, B01000000, B10000000, B01000000 }; static const unsigned char PROGMEM BaseGfx [] = { B00011111,B11111000, B01111111,B11111110, B11111111,B11111111, B11111111,B11111111, B11111111,B11111111, B11111000,B00011111, B11100000,B00000111, B11100000,B00000111 }; // 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 BaseStruct { GameObjectStruct Ord; unsigned char Gfx[16]; }; struct AlienStruct { GameObjectStruct Ord; unsigned char ExplosionGfxCounter; // how long we want the ExplosionGfx to last }; struct PlayerStruct { GameObjectStruct Ord; unsigned int Score; unsigned char Lives; unsigned char Level; unsigned char AliensDestroyed; // count of how many killed so far unsigned char AlienSpeed; // higher the number slower they go, calculated when ever alien destroyed unsigned char ExplosionGfxCounter; // how long we want the ExplosionGfx to last }; // 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; GameObjectStruct AlienBomb[MAXBOMBS]; BaseStruct Base[NUM_BASES]; static const int TOTAL_ALIENS=NUM_ALIEN_COLUMNS*NUM_ALIEN_ROWS; //NEW // 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; // game variables unsigned int HiScore; bool GameInPlay=false; 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); EEPROM.get(0,HiScore); if(HiScore==65535) // new unit never written to { HiScore=0; EEPROM.put(0,HiScore); } } void loop() { //NEW if(GameInPlay) { Physics(); UpdateDisplay(); } else AttractScreen(); } void AttractScreen() { display.clearDisplay(); CentreText("Play",0); CentreText("Space Invaders",12); CentreText("Press Fire to start",24); CentreText("Hi Score ",36); display.setCursor(80,36); display.print(HiScore); display.display(); if(digitalRead(FIRE_BUT)==0){ GameInPlay=true; NewGame(); } // CHECK FOR HIGH SCORE RESET, PLAYER MUST HOLD LEFT AND RIGHT TOGETHER if((digitalRead(LEFT_BUT)==0)&(digitalRead(RIGHT_BUT)==0)) { // Reset high score, don't need to worry about debounce as will ony write to EEPROM if changed, so writes a 0 then won't write again // if hiscore still 0 which it will be HiScore=0; EEPROM.put(0,HiScore); } } void Physics() { if(Player.Ord.Status==ACTIVE) { AlienControl(); MotherShipPhysics(); PlayerControl(); MissileControl(); CheckCollisions(); } } unsigned char GetScoreForAlien(int RowNumber) { // returns value for killing and alien at the row indicated switch (RowNumber) { case 0:return 30; case 1:return 20; case 2:return 10; } } 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=Player.AlienSpeed; AnimationFrame=!AnimationFrame; ///swap to other frame } // should the alien drop a bomb if(random(CHANCEOFBOMBDROPPING)==1) DropBomb(); MoveBombs(); } void MoveBombs(){ for(int i=0;i<MAXBOMBS;i++){ if(AlienBomb[i].Status==ACTIVE) AlienBomb[i].Y+=2; } } void DropBomb() { // if there is a free bomb slot then drop a bomb else nothing happens bool Free=false; unsigned char ActiveCols[NUM_ALIEN_COLUMNS]; unsigned char BombIdx=0; // find a free bomb slot while((Free==false)&(BombIdx<MAXBOMBS)){ if(AlienBomb[BombIdx].Status==DESTROYED) Free=true; else BombIdx++; } if(Free) { unsigned char Columns=0; // now pick and alien at random to drop the bomb // we first pick a column, obviously some columns may not exist, so we count number of remaining cols // first, this adds time but then also picking columns randomly that don't exist may take time also unsigned char ActiveColCount=0; signed char Row; unsigned char ChosenColumn; while(Columns<NUM_ALIEN_COLUMNS){ Row=2; while(Row>=0) { if(Alien[Columns][Row].Ord.Status==ACTIVE) { ActiveCols[ActiveColCount]=Columns; ActiveColCount++; break; } Row--; } Columns++; } // we have ActiveCols array filled with the column numbers of the active cols and we have how many // in ActiveColCount, now choose a column at random ChosenColumn=random(ActiveColCount); // random number between 0 and the amount of columns // we now find the first available alien in this column to drop the bomb from Row=2; while(Row>=0) { if(Alien[ActiveCols[ChosenColumn]][Row].Ord.Status==ACTIVE) { // Set the bomb from this alien AlienBomb[BombIdx].Status=ACTIVE; AlienBomb[BombIdx].X=Alien[ActiveCols[ChosenColumn]][Row].Ord.X+int(AlienWidth[Row]/2); // above sets bomb to drop around invaders centre, here we add a litrle randomness around this pos AlienBomb[BombIdx].X=(AlienBomb[BombIdx].X-2)+random(0,4); AlienBomb[BombIdx].Y=Alien[ActiveCols[ChosenColumn]][Row].Ord.Y+4; break; } Row--; } } } void BombCollisions() { //check bombs collisions for(int i=0;i<MAXBOMBS;i++) { if(AlienBomb[i].Status==ACTIVE) { if(AlienBomb[i].Y>64) // gone off bottom of screen AlienBomb[i].Status=DESTROYED; else { // HAS IT HIT PLAYERS missile if(Collision(AlienBomb[i],BOMB_WIDTH,BOMB_HEIGHT,Missile,MISSILE_WIDTH,MISSILE_HEIGHT)) { // destroy missile and bomb AlienBomb[i].Status=EXPLODING; Missile.Status=DESTROYED; } else { // has it hit players ship if(Collision(AlienBomb[i],BOMB_WIDTH,BOMB_HEIGHT,Player.Ord,TANKGFX_WIDTH,TANKGFX_HEIGHT)) { PlayerHit(); AlienBomb[i].Status=DESTROYED; } else BombAndBasesCollision(&AlienBomb[i]); } } } } } void BombAndBasesCollision(GameObjectStruct *Bomb) { // check and handle any bomb and base collision for(int i=0;i<NUM_BASES;i++) { if(Collision(*Bomb,BOMB_WIDTH,BOMB_HEIGHT,Base[i].Ord,BASE_WIDTH,BASE_HEIGHT)) { // Now get the position of the bomb within the structure so we can destroy it bit by bit // we first get the relative position from the left hand side of the base // then we divide this by 2 (X>>1) , this gives us a position with 2bit resolution unsigned char X=Bomb->X-Base[i].Ord.X; X=X>>1; // Because the bomb is 2 pixels wide it's X pos could have been less than the bases XPos, if this is the case the above substaction // on an unsigned char (byte) will cause a large number to occur (255), we check for this and if this large number has // resulted we just set X to 0 for the start of the bases structure if(X>7) X=0; // We now look at wether the bomb is hitting a part of the structure below it. // the bomb may be past the top of the base (even on first collision detection) as it moves in Y amounts greater than 1 pixel to give a higher speed // so we start from top of the base and destroy any structure of the base that comes before or equal to the // bombs Y pos, if we go past the bomb Y without finding any bit of base then stop looking and bomb is allowed to progress further down signed char Bomb_Y=(Bomb->Y+BOMB_HEIGHT)-Base[i].Ord.Y; unsigned char Base_Y=0; while((Base_Y<=Bomb_Y)&(Base_Y<BASE_HEIGHT)&(Bomb->Status==ACTIVE)) { unsigned char Idx=(Base_Y*BASE_WIDTH_IN_BYTES)+(X>>2); // this gets the index for the byte in question from the gfx array unsigned char TheByte=Base[i].Gfx[Idx]; // we now have the byte to inspect, but need to only look at the 2 bits where the bomb is colliding // now isolate the 2 bits in question, we have the correct byte and we only have need the bottom 2 bits of X now to denote which bits // we need to destroy in the byte itself unsigned char BitIdx=X & 3; // this preseves the bottom 2 bits and removes the rest // A value of X of 0 (zero) would mean we want to look at the first 2 bits of the byte // A value of X of 1 (zero) would mean we want to look at the second 2 bits of the byte // A value of X of 2 (zero) would mean we want to look at the third 2 bits of the byte // A value of X of 3 (zero) would mean we want to look at the fourth 2 bits of the byte // So we need an AND mask to isolate these bits depending on the value of X // Here it is and we initially set it to the first 2 bits unsigned char Mask=B11000000; // now we need to move those 2 "11"'s to the right depending on the value of X as noted above // the next line may look odd but all we're doing is multiplying X by 2 initially, so the values above would become,0,2,4,6 rather than 0,1,2,3 // Then we move the bits in the mask by this new amount, check it above,a value of X of 2 would shift the bits 4 places, whichis correct! Mask=Mask>>(BitIdx<<1); //now we peform a logical and to remove all bits (pixels) from around these two bits TheByte=TheByte & Mask; // and if there are any set pixels (bits) then they must be destroyed, else the bomb is allowed to continue if(TheByte>0) { // There are some pixels to destroy //We need to remove the pixels(bits) where there were "11"'s in the mask and leave those intact where there were 0's //easiest way, flip all 0's in the mask to ones and all 1's to 0's, the tilde "~" means invert (swap), reffered to as logical NOT Mask=~Mask; // we can then "AND" the byte with the Mask to remove the bits but leave the rest intact Base[i].Gfx[Idx]=Base[i].Gfx[Idx] & Mask; // now do some collateral damage to surrounding bricks, try left hand side first if(X>0){ // not at far left, if we were there would be nothing to destroy to this left if(random(CHANCE_OF_BOMB_DAMAGE_TO_LEFT_OR_RIGHT)) // if true blow some bricks to the left hand side { if(X!=4) // we not at start of second byte { Mask=(Mask<<1)|1; Base[i].Gfx[Idx]=Base[i].Gfx[Idx] & Mask; } else // we are at very start of second byte, so wipe out adjacent pixel first byte { Base[i].Gfx[Idx-1]=Base[i].Gfx[Idx-1] & B11111110; } } } // now do some collateral damage right hand side first if(X<7){ // not at far right, if we were there would be nothing to destroy to this right if(random(CHANCE_OF_BOMB_DAMAGE_TO_LEFT_OR_RIGHT)) // if true blow some bricks to the left hand side { if(X!=3) // not at last pixel of left of first byte { Mask=(Mask>>1)|128; Base[i].Gfx[Idx]=Base[i].Gfx[Idx] & Mask; } else // we are at last pixel of first byte so destroy pixil in adjacent byte { Base[i].Gfx[Idx+1]=Base[i].Gfx[Idx+1] & B01111111; } } } if(random(CHANCE_OF_BOMB_PENETRATING_DOWN)==false) // if false BOMB EXPLODES else carries on destroying more Bomb->Status=EXPLODING; } else Base_Y++; } } } } void MissileAndBasesCollisions() { // check and handle any player missile and base collision for(int i=0;i<NUM_BASES;i++) { if(Collision(Missile,MISSILE_WIDTH,MISSILE_HEIGHT,Base[i].Ord,BASE_WIDTH,BASE_HEIGHT)) { // Now get the position of the bomb within the structure so we can destroy it bit by bit // we first get the relative position from the left hand side of the base // then we divide this by 2 (X>>1) , this gives us a position with 2bit resolution unsigned char X=Missile.X-Base[i].Ord.X; X=X>>1; // Because the bomb is 2 pixels wide it's X pos could have been less than the bases XPos, if this is the case the above substaction // on an unsigned char (byte) will cause a large number to occur (255), we check for this and if this large number has // resulted we just set X to 0 for the start of the bases structure if(X>7) X=0; // We now look at wether the bomb is hitting a part of the structure above it. // the bomb may be past the top of the base (even on first collision detection) as it moves in Y amounts greater than 1 pixel to give a higher speed // so we start from top of the base and destroy any structure of the base that comes before or equal to the // bombs Y pos, if we go past the bomb Y without finding any bit of base then stop looking and bomb is allowed to progress further down signed char Missile_Y=Missile.Y-Base[i].Ord.Y; signed char Base_Y=BASE_HEIGHT-1; while((Base_Y>=Missile_Y)&(Base_Y>=0)&(Missile.Status==ACTIVE)) { // if(Base_Y<0) {Serial.println("oop"); delay(999999);} unsigned char Idx=(Base_Y*BASE_WIDTH_IN_BYTES)+(X>>2); // this gets the index for the byte in question from the gfx array unsigned char TheByte=Base[i].Gfx[Idx]; // we now have the byte to inspect, but need to only look at the 2 bits where the bomb is colliding // now isolate the 2 bits in question, we have the correct byte and we only have need the bottom 2 bits of X now to denote which bits // we need to destroy in the byte itself unsigned char BitIdx=X & 3; // this preseves the bottom 2 bits and removes the rest // A value of X of 0 (zero) would mean we want to look at the first 2 bits of the byte // A value of X of 1 (zero) would mean we want to look at the second 2 bits of the byte // A value of X of 2 (zero) would mean we want to look at the third 2 bits of the byte // A value of X of 3 (zero) would mean we want to look at the fourth 2 bits of the byte // So we need an AND mask to isolate these bits depending on the value of X // Here it is and we initially set it to the first 2 bits unsigned char Mask=B11000000; // now we need to move those 2 "11"'s to the right depending on the value of X as noted above // the next line may look odd but all we're doing is multiplying X by 2 initially, so the values above would become,0,2,4,6 rather than 0,1,2,3 // Then we move the bits in the mask by this new amount, check it above,a value of X of 2 would shift the bits 4 places, whichis correct! Mask=Mask>>(BitIdx<<1); //now we peform a logical AND to remove all bits (pixels) from around these two bits TheByte=TheByte & Mask; // and if there are any set pixels (bits) then they must be destroyed, else the bomb is allowed to continue if(TheByte>0) { // There are some pixels to destroy //We need to remove the pixels(bits) where there were "11"'s in the mask and leave those intact where there were 0's //easiest way, flip all 0's in the mask to ones and all 1's to 0's, the tilde "~" means invert (swap), reffered to as logical NOT Mask=~Mask; // we can then "AND" the byte with the Mask to remove the bits but leave the rest intact Base[i].Gfx[Idx]=Base[i].Gfx[Idx] & Mask; // now do some collateral damage to surrounding bricks, try left hand side first if(X>0){ // not at far left, if we were there would be nothing to destroy to this left if(random(CHANCE_OF_BOMB_DAMAGE_TO_LEFT_OR_RIGHT)) // if true blow some bricks to the left hand side { if(X!=4) // we not at start of second byte { Mask=(Mask<<1)|1; Base[i].Gfx[Idx]=Base[i].Gfx[Idx] & Mask; } else // we are at very start of second byte, so wipe out adjacent pixel first byte { Base[i].Gfx[Idx-1]=Base[i].Gfx[Idx-1] & B11111110; } } } // now do some collateral damage right hand side first if(X<7){ // not at far right, if we were there would be nothing to destroy to this right if(random(CHANCE_OF_BOMB_DAMAGE_TO_LEFT_OR_RIGHT)) // if true blow some bricks to the left hand side { if(X!=3) // not at last pixel of left of first byte { Mask=(Mask>>1)|128; Base[i].Gfx[Idx]=Base[i].Gfx[Idx] & Mask; } else // we are at last pixel of first byte so destroy pixil in adjacent byte { Base[i].Gfx[Idx+1]=Base[i].Gfx[Idx+1] & B01111111; } } } if(random(CHANCE_OF_BOMB_PENETRATING_DOWN)==false) // if false BOMB EXPLODES else carries on destroying more Missile.Status=EXPLODING; } else Base_Y--; } } } } void PlayerHit() { Player.Ord.Status=EXPLODING; Player.ExplosionGfxCounter=PLAYER_EXPLOSION_TIME; Missile.Status=DESTROYED; } void CheckCollisions() { MissileAndAlienCollisions(); MotherShipCollisions(); MissileAndBasesCollisions(); BombCollisions(); AlienAndBaseCollisions(); } char GetAlienBaseCollisionMask(int AlienX, int AlienWidth,int BaseX) { signed int DamageWidth; unsigned char LeftMask,RightMask,FullMask; // this routine uses a 1 to mean remove bit and 0 to preserve, this is kind of opposite of what we would // normally think of, but it's done this way as when we perform bit shifting to show which bits are preserved // it will shift in 0's in (as that's just was the C shift operater ">>" and "<<" does // at the end we will flip all the bits 0 becomes 1, 1 becomes 0 etc. so that the mask then works correctly // with the calling code LeftMask=B11111111; // initially set to remove all RightMask=B11111111; // unless change in code below // if Alien X more than base x then some start bits are unaffected if(AlienX>BaseX) { // we shift the bits above to the right by the amount unaffected, thus putting 0's into the bits // not to delete DamageWidth=AlienX-BaseX; LeftMask>>=DamageWidth; } // now work out how much of remaining byte is affected // if right hand side of alien is less than BaseX right hand side then some preserved at the right hand end if(AlienX+AlienWidth<BaseX+(BASE_WIDTH/2)) { DamageWidth=(BaseX+(BASE_WIDTH/2))-(AlienX+AlienWidth); RightMask<<=DamageWidth; } // we now have two masks, one showing which bits to preserve on left of the byte, the other the right hand side, // we need to combine them to one mask, the code in the brackets does this combining // at the moment a 0 means keep, 1 destroy, but this is actually makes it difficult to implement later on, so we flip // the bits to be a more logical 1= keep bit and 0 remove bit (pixel) and then return the mask // the tilde (~) flips the bits that resulted from combining the two masks return ~(LeftMask & RightMask); } void DestroyBase(GameObjectStruct *Alien,BaseStruct *Base,char Mask,int BaseByteOffset) { signed char Y; // go down "removing" bits to the depth that the alien is down into the base Y=(Alien->Y+ALIEN_HEIGHT)-Base->Ord.Y; if(Y>BASE_HEIGHT-1) Y=BASE_HEIGHT-1; for(;Y>=0;Y--){ Base->Gfx[(Y*2)+BaseByteOffset]=Base->Gfx[(Y*2)+BaseByteOffset] & Mask; } } void AlienAndBaseCollisions() { unsigned char Mask; // checks if aliens are in collision with the tank // start at bottom row as they are most likely to be in contact or not and if not then none further up are either for(int row=2;row>=0;row--) { for(int column=0;column<NUM_ALIEN_COLUMNS;column++) { if(Alien[column][row].Ord.Status==ACTIVE) { // now scan for a collision with each base in turn for(int BaseIdx=0;BaseIdx<NUM_BASES;BaseIdx++) { if(Collision(Alien[column][row].Ord,AlienWidth[row],ALIEN_HEIGHT,Base[BaseIdx].Ord,BASE_WIDTH,BASE_HEIGHT)) { // WE HAVE A COLLSISION, REMOVE BITS OF BUILDING // process left half (first byte) of base first Mask=GetAlienBaseCollisionMask(Alien[column][row].Ord.X,AlienWidth[row],Base[BaseIdx].Ord.X); DestroyBase(&Alien[column][row].Ord,&Base[BaseIdx],Mask,0); // do right half, second byte of base Mask=GetAlienBaseCollisionMask(Alien[column][row].Ord.X,AlienWidth[row],Base[BaseIdx].Ord.X+(BASE_WIDTH/2)); DestroyBase(&Alien[column][row].Ord,&Base[BaseIdx],Mask,1); } } } } } } 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; } Player.Score+=MotherShipBonus; 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; Player.Score+=GetScoreForAlien(down); Player.AliensDestroyed++; // calc new speed of aliens, note (float) must be before TOTAL_ALIENS to force float calc else // you will get an incorrect result Player.AlienSpeed=((1-(Player.AliensDestroyed/(float)TOTAL_ALIENS))*INVADERS_SPEED); // for very last alien make to fast! if(Player.AliensDestroyed==TOTAL_ALIENS-2) if(AlienXMoveAmount>0) AlienXMoveAmount=ALIEN_X_MOVE_AMOUNT*2; else AlienXMoveAmount=-(ALIEN_X_MOVE_AMOUNT*2); // for very last alien make to super fast! if(Player.AliensDestroyed==TOTAL_ALIENS-1) if(AlienXMoveAmount>0) AlienXMoveAmount=ALIEN_X_MOVE_AMOUNT*4; else AlienXMoveAmount=-(ALIEN_X_MOVE_AMOUNT*4); if(Player.AliensDestroyed==TOTAL_ALIENS) NextLevel(&Player); } } if(Alien[across][down].Ord.Status==ACTIVE) // double check still active afer above code { // check if this alien is in contact with TankGfx if(Collision(Player.Ord,TANKGFX_WIDTH,TANKGFX_HEIGHT,Alien[across][down].Ord,AlienWidth[down],ALIEN_HEIGHT)) PlayerHit(); else { // check if alien is below bottom of screen if(Alien[across][down].Ord.Y+8>SCREEN_HEIGHT) PlayerHit(); } } } } } } 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--; } else { // draw score and lives, anything else can go above them display.setCursor(0,0); display.print(Player.Score); display.setCursor(SCREEN_WIDTH-7,0); display.print(Player.Lives); } //BOMBS // draw bombs next as aliens have priority of overlapping them for(i=0;i<MAXBOMBS;i++) { if(AlienBomb[i].Status==ACTIVE) display.drawBitmap(AlienBomb[i].X, AlienBomb[i].Y, AlienBombGfx, 2, 4,WHITE); else {// must be destroyed if(AlienBomb[i].Status==EXPLODING) display.drawBitmap(AlienBomb[i].X-4, AlienBomb[i].Y, ExplosionGfx, 4, 8,WHITE); // Ensure on next draw that ExplosionGfx dissapears AlienBomb[i].Status=DESTROYED; } } //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 if(Player.Ord.Status==ACTIVE) display.drawBitmap(Player.Ord.X, Player.Ord.Y, TankGfx, TANKGFX_WIDTH, TANKGFX_HEIGHT,WHITE); else { if(Player.Ord.Status==EXPLODING) { for(i=0;i<TANKGFX_WIDTH;i+=2) { display.drawBitmap(Player.Ord.X+i, Player.Ord.Y, ExplosionGfx, random(4)+2, 8,WHITE); } Player.ExplosionGfxCounter--; if(Player.ExplosionGfxCounter==0) { Player.Ord.Status=DESTROYED; LoseLife(); } } } //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; } } } // plot bases for(i=0;i<NUM_BASES;i++) { if(Base[i].Ord.Status==ACTIVE) display.drawBitmap(Base[i].Ord.X, Base[i].Ord.Y, Base[i].Gfx, BASE_WIDTH, BASE_HEIGHT,WHITE,true); } display.display(); } void LoseLife() { Player.Lives--; if(Player.Lives>0) { DisplayPlayerAndLives(&Player); // clear alien missiles for(int i=0;i<MAXBOMBS;i++) { AlienBomb[i].Status=DESTROYED; AlienBomb[i].Y=0; } // ENABLE PLAYER Player.Ord.Status=ACTIVE; Player.Ord.X=0; } else { GameOver(); } } void GameOver() { GameInPlay=false; display.clearDisplay(); CentreText("Player 1",0); CentreText("Game Over",12); CentreText("Score ",24); display.print(Player.Score); if(Player.Score>HiScore) { CentreText("NEW HIGH SCORE!!!",36); CentreText("**CONGRATULATIONS**",48); } display.display(); if(Player.Score>HiScore){ HiScore=Player.Score; EEPROM.put(0,HiScore); } delay(2500); } void DisplayPlayerAndLives(PlayerStruct *Player) { display.clearDisplay(); CentreText("Player 1",0); CentreText("Score ",12); display.print(Player->Score); CentreText("Lives ",24); display.print(Player->Lives); CentreText("Level ",36); display.print(Player->Level); display.display(); delay(2000); Player->Ord.X=PLAYER_X_START; } void CentreText(const char *Text,unsigned char Y) { // centres text on screen display.setCursor(int((float)(SCREEN_WIDTH)/2-((strlen(Text)*6)/2)),Y); display.print(Text); } void InitPlayer() { Player.Ord.Y=PLAYER_Y_START; Player.Ord.X=PLAYER_X_START; Player.Ord.Status=ACTIVE; Player.Lives=LIVES; Player.Level=0; Missile.Status=DESTROYED; Player.Score=0; } void NextLevel(PlayerStruct *Player) { // reset any dropping bombs int YStart; for(int i=0;i<MAXBOMBS;i++) AlienBomb[i].Status=DESTROYED; AnimationFrame=false; Player->Level++; YStart=((Player->Level-1) % LEVEL_TO_RESET_TO_START_HEIGHT)*AMOUNT_TO_DROP_BY_PER_LEVEL; InitAliens(YStart); AlienXMoveAmount=ALIEN_X_MOVE_AMOUNT; Player->AlienSpeed=INVADERS_SPEED; Player->AliensDestroyed=0; MotherShip.Ord.X=-MOTHERSHIP_WIDTH; MotherShip.Ord.Status=DESTROYED; Missile.Status=DESTROYED; randomSeed(100); InitBases(); DisplayPlayerAndLives(Player); } void InitBases() { // Bases need to be re-built! uint8_t TheByte; int Spacing=(SCREEN_WIDTH-(NUM_BASES*BASE_WIDTH))/NUM_BASES; for(int i=0;i<NUM_BASES;i++) { for(int DataIdx=0;DataIdx<BASE_HEIGHT*BASE_WIDTH_IN_BYTES;DataIdx++) { TheByte = pgm_read_byte(BaseGfx + DataIdx); Base[i].Gfx[DataIdx]=TheByte; } Base[i].Ord.X=(i*Spacing)+(i*BASE_WIDTH)+(Spacing/2); Base[i].Ord.Y=BASE_Y; Base[i].Ord.Status=ACTIVE; } } void NewGame(){ InitPlayer(); NextLevel(&Player); } 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; } } MotherShip.Ord.Y=0; MotherShip.Ord.X=-MOTHERSHIP_WIDTH; MotherShip.Ord.Status=DESTROYED; } |
The next article/episode will be the penultimate one where we will add sound to our game. See you next time!