Soviet Bloc Game (C version)

While thinking about ways to make my TRS-80 model I more useable in 2019, I realized that I could not easily find a version of Tetris for it (probably because the TRS-80 came out about 10ish years before Tetris was invented), so I thought I might try to write my own after watching an episode of the 8-bit Guy where David does the same. I used to play the Gameboy version of Tetris all the time on my Ti-nSpire calculator thanks to the nspire hacking scene and an emulator port, so that's the style of Tetris I will try to recreate.

Objectives:

• Playfield the same size as GB version
• in color?
• same or similar scoring system to GB version
• same rotation style as GB version
• easily portable to different platforms (that are C like)
• somewhat documented

This ended up being a sort of 24 hour challenge; I started this project at about 11pm yesterday, and by about the time of this page's creation I had created an Arduino version of Tetris that met most of these objectives.

Theory of Operation

Basics

The basics of the game's functioning can be summed up with just a few components: a part that generates the tetrominoe shapes, a playfield that contains already played pieces and open spots where the active piece can move and collision detection that says where the active piece can and can't go.

The playfield size is adjustable, but in the gameboy version it's 10 wide by 18 tall. In my version I added an extra 4 lines on top (which are not to be displayed) for the new pieces to appear within. Within the program, it appears as a big 2D matrix called playfield[][].

Drawing the pieces

Rather than figure out all the complex rotations of the part, I hardcoded them (using the Nintendo rotation system as described at https://tetris.fandom.com/wiki/Nintendo_Rotation_System). The parts appear in a 4x4 piece container pieceC[][] matrix. This is then overlaid onto the playfield, and can be moved around. Nonzero cells of the matrix define the shape of the piece, like:

0	0	0	0
0	5	0	0
5	5	0	0
0	5	0	0

The numbers used to define the piece are unique to each piece, so if you write the display section to use each number as a color, you can have a color game.

Collision detection

In the collision detection section, the overlaid piece carrier is moved as if you were to make that move, and then we check if any of the cells overlap with non-blank sections of the playfield, or if any part of the active piece lies outside the playfield area. If so, the move is undone, and you can decide what to do from there. If no collision occurs, the move is done for real and displayed the next time the screen is updated.

Usually, the collision detection is used to prevent motion if a piece or wall is in the way, but if the piece is attempting to move downwards, the piece is instead copied onto the playfield, and the numbers making up the piece are increased by 8. This is how the collision detection can differentiate between the active piece and dead pieces in the playfield.

Input conditioning

I added some input conditioning as well. For rotations of the active piece, the move is not repeating, and you must release the rotation input and press it again for a rotation to happen again. For moves left, right, and down, a system similar to repeating keys on a computer keyboard is used, holding down the direction for a brief moment will make the action repeat. In the gameboy version, dropping a piece quickly will increase the score based on the number of tiles dropped while moving fast. This is also replicated (but probably not perfectly) in my version.

The Code (Arduino version)

#define pfsizeX 10
#define pfsizeY 22 //note that top 4 lines are not drawn
uint8_t playfield[pfsizeX][pfsizeY];  //the game area

uint8_t pieceC[4][4]; //piece container
int8_t pieceCX;  //location of upper left corner of piece container
int8_t pieceCY;
uint8_t pieceT; //type of piece
uint8_t pieceR; //rotation of piece 
uint8_t nextpieceT; 
uint8_t nextpieceR; 

uint8_t dcontrol; //locks in control every frame
uint8_t rcontrol;

uint8_t lastdcontrol=0; //for "debouncing" of inputs
uint8_t lastrcontrol=0; 
uint8_t drepeatframe=0;
#define drepeatframes 3 //wait _ frames before repeatedly going in one direction

uint8_t dropframe=0;    //counter for number of frames between block drops
uint8_t level=0; //LEVEL decreases frame drop from 20 frames to 0 frames (levels 0 to 20)

boolean ngame=0; //when set, starts new game

uint16_t lines=0; //NUMBER OF LINES CLEARED
uint32_t score=0; //TOTAL SCORE (using NES rules)

uint8_t fdrop;   //number of blocks that piece has been fast dropped
uint8_t lslvi=0; //lines since level increase (when this gets to 10, increase the level)

#include <U8g2lib.h>
U8G2_ST7920_128X64_1_HW_SPI u8g2(U8G2_R0, /* CS=*/ 12, /* reset=*/ 8);

void dispscreen(){
  u8g2.firstPage();  
  do {
    for(uint8_t j=4; j<pfsizeY; j++){ //draw screen
    for(uint8_t i=0; i<pfsizeX; i++){
      if(playfield[i][j]!=0){
        u8g2.drawBox(5*(j-4),5*(pfsizeX-1)-5*i,6,6);
      }else{
        u8g2.drawFrame(5*(j-4),5*(pfsizeX-1)-5*i,6,6);
        //if(j==3){u8g2.drawLine(5*j,5*(pfsizeX-1)-5*i,5*j+5,5*(pfsizeX-1)-5*i+5);}
      }
    }}

  uint8_t temppieceT=pieceT; 
  uint8_t temppieceR=pieceR;
  pieceT=nextpieceT;
  pieceR=nextpieceR;
  loadpiece(); 
  for(uint8_t j=0; j<4; j++){ //draw next piece
  for(uint8_t i=0; i<4; i++){
    if(pieceC[i][j]!=0){
      u8g2.drawBox(5*(j+pfsizeY-3),5*(pfsizeX-1)-5*i,6,6);
    }else{
      u8g2.drawFrame(5*(j+pfsizeY-3),5*(pfsizeX-1)-5*i,6,6);
    }
  }}
  pieceT=temppieceT;
  pieceR=temppieceR;
  loadpiece();

  u8g2.setFont(u8g2_font_6x10_tf);
  char zbuffer[32];
  sprintf(zbuffer, "N%d", lines);
  u8g2.drawStr(0,60, zbuffer);
  sprintf(zbuffer, "L%d", level);
  u8g2.drawStr(25,60, zbuffer);
  sprintf(zbuffer, "S%d", score);
  u8g2.drawStr(50,60, zbuffer);  
  } while( u8g2.nextPage() );
}

void controls(){
  if(digitalRead(A3)==0){ngame=1;}
  if(dcontrol==0){
    if(analogRead(A7)<10){dcontrol=4;}
    if(analogRead(A7)>1014){dcontrol=6;}
    if(analogRead(A6)>1014){dcontrol=8;}
    if(analogRead(A6)<10){dcontrol=2;}
    if(dcontrol==0){drepeatframe=0;}
    if(dcontrol==lastdcontrol){          //short delay before fast motion
      if(drepeatframe<=drepeatframes){
        drepeatframe++;
        dcontrol=3; //lockout if within lockout period
      }
    }
  }
  if(rcontrol==0){
    if(digitalRead(A4)==0){rcontrol=1;}
    if(digitalRead(A5)==0){rcontrol=2;}
    if(rcontrol==lastrcontrol){rcontrol=3;}
  }
}

void clearControls(){
  if(rcontrol!=3){lastrcontrol=rcontrol;}
  if(dcontrol!=3){lastdcontrol=dcontrol;}
  rcontrol=0;
  dcontrol=0;
}

void draw(){
  loadpiece(); //load piece into the piece carrier
  for(uint8_t i=0; i<pfsizeX; i++){   //clear any cells with active piece parts (will be written again with new pieceC
    for(uint8_t j=0; j<pfsizeY; j++){
      if(playfield[i][j]<=7){playfield[i][j]=0;}
    }
  }
  for(uint8_t i=0; i<4; i++){ //copy active piece onto the playfield
    for(uint8_t j=0; j<4; j++){
      if(pieceCX+i>=0&&pieceCX+i<pfsizeX&&pieceCY+j>=0&&pieceCY+j<pfsizeY){//check if piece segment can be drawn on screen
        if(pieceC[i][j]!=0){playfield[i+pieceCX][j+pieceCY]=pieceC[i][j];}
      }
    }
  }
}

boolean checkCollide(){ //move the piece carrier first, then check if anything collides
  loadpiece(); //load piece into the piece carrier
  boolean nonvalidity=0;
  for(uint8_t i=0; i<4; i++){ //run through all piece carrier cells
    for(uint8_t j=0; j<4; j++){
      if(pieceCX+i>=0&&pieceCX+i<pfsizeX&&pieceCY+j>=0&&pieceCY+j<pfsizeY){ //check if piece carrier segment can be drawn on screen
        if(pieceC[i][j]!=0&&playfield[i+pieceCX][j+pieceCY]>7){ //if both background and nonzero piece carrier segment collide
          nonvalidity=1;
        }
      }else{ //this segment of PC can't be drawn on the screen
        if(pieceC[i][j]!=0){ //a filled in segment would be drawn offscreen
          nonvalidity=1;
        }
      }
    }
  }
  return nonvalidity;
}

void piece2bg(){
  for(uint8_t i=0; i<4; i++){ //copy active piece onto the screen
  for(uint8_t j=0; j<4; j++){
    if(pieceC[i][j]!=0){playfield[i+pieceCX][j+pieceCY]=pieceC[i][j]+8;} //copy the piece into the playfield/background 
  }}
  nextpiece();
}

void nextpiece(){//generate the next piece and move PC back to the top
  pieceT=nextpieceT;
  pieceR=nextpieceR;
  nextpieceT = rand()%7 + 1;
  nextpieceR = rand()%4 + 1;
  pieceCY=0; //move piece carrier back to the top of screen
  pieceCX=3;
}

void newgamemon(){
  if(ngame==0){return;}
  Serial.println(F("NEW GAME"));
  ngame=0;
  for(uint8_t i=0; i<pfsizeX; i++){   //clear any cells with active piece parts (will be written again with new pieceC
    for(uint8_t j=0; j<pfsizeY; j++){
      playfield[i][j]=0;
    }
  }
  lines=0;
  level=0;
  score=0;
  lslvi=0;
  fdrop=0;
  nextpiece();
  nextpiece();
}

void loadpiece(){ //hardcoded all pieces
  switch(pieceT){
    case 1: //long one
     switch(pieceR){
      case 1:
      case 3:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=1; pieceC[1][2]=1; pieceC[2][2]=1; pieceC[3][2]=1;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=0; pieceC[3][3]=0; 
        break;
      case 2:
      case 4:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=1; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=1; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=0; pieceC[2][2]=1; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=1; pieceC[3][3]=0; 
        break;
     }
     break;
   case 2: //backwards L
     switch(pieceR){
      case 1:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=2; pieceC[1][2]=2; pieceC[2][2]=2; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=2; pieceC[3][3]=0;
        break;
      case 2:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=2; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=2; pieceC[2][2]=0; pieceC[3][2]=0;
        pieceC[0][3]=2; pieceC[1][3]=2; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 3:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=2; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=2; pieceC[1][2]=2; pieceC[2][2]=2; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 4:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=2; pieceC[2][1]=2; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=2; pieceC[2][2]=0; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=2; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
     }
     break;
   case 3: //L
     switch(pieceR){
      case 1:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=3; pieceC[1][2]=3; pieceC[2][2]=3; pieceC[3][2]=0;
        pieceC[0][3]=3; pieceC[1][3]=0; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 2:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=3; pieceC[1][1]=3; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=3; pieceC[2][2]=0; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=3; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 3:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=3; pieceC[3][1]=0;
        pieceC[0][2]=3; pieceC[1][2]=3; pieceC[2][2]=3; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 4:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=3; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=3; pieceC[2][2]=0; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=3; pieceC[2][3]=3; pieceC[3][3]=0;
        break;
     }
     break;
   case 4: //s shape
     switch(pieceR){
      case 1:
      case 3:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=4; pieceC[2][2]=4; pieceC[3][2]=0;
        pieceC[0][3]=4; pieceC[1][3]=4; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 2:
      case 4:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=4; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=4; pieceC[2][2]=4; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=4; pieceC[3][3]=0;
        break;
     }
     break;
   case 5: //T shape
     switch(pieceR){
      case 1:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=5; pieceC[1][2]=5; pieceC[2][2]=5; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=5; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 2:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=5; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=5; pieceC[1][2]=5; pieceC[2][2]=0; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=5; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 3:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=5; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=5; pieceC[1][2]=5; pieceC[2][2]=5; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
      case 4:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=5; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=5; pieceC[2][2]=5; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=5; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
     }
     break;
   case 6: //reverse s
     switch(pieceR){
      case 1:
      case 3:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=0; pieceC[3][1]=0;
        pieceC[0][2]=6; pieceC[1][2]=6; pieceC[2][2]=0; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=6; pieceC[2][3]=6; pieceC[3][3]=0;
        break;
      case 2:
      case 4:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=0; pieceC[2][1]=6; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=6; pieceC[2][2]=6; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=6; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
     }
     break;
   case 7: //square
     switch(pieceR){
      default:
        pieceC[0][0]=0; pieceC[1][0]=0; pieceC[2][0]=0; pieceC[3][0]=0;
        pieceC[0][1]=0; pieceC[1][1]=7; pieceC[2][1]=7; pieceC[3][1]=0;
        pieceC[0][2]=0; pieceC[1][2]=7; pieceC[2][2]=7; pieceC[3][2]=0;
        pieceC[0][3]=0; pieceC[1][3]=0; pieceC[2][3]=0; pieceC[3][3]=0;
        break;
     }
     break;
  }
}

void setup(){
  Serial.begin(115200);
  u8g2.begin();
  pinMode(A4, INPUT_PULLUP);
  pinMode(A5, INPUT_PULLUP);
  pinMode(A3, INPUT_PULLUP); //new game button

  ngame=1;
  newgamemon();
}

void loop() {
  
  for(uint32_t h=0;h<=5;h++){//frame delay  //DELAY SECTION (BETWEEN FRAMES)
    delay(1);
    controls();
    newgamemon();
  }
  
  boolean droppiece=0;
  dropframe++;
  if(dropframe>=(20-level)){
    dropframe=0;
    droppiece=1;
  }
  
  if(rcontrol==1){
    pieceR++; if(pieceR>=5){pieceR=1;} //try to rotate piece
    if(checkCollide()){
      pieceR--; if(pieceR<=0){pieceR=4;} //undo rotation
    }
  }
  if(rcontrol==2){
    pieceR--; if(pieceR<=0){pieceR=4;}
    if(checkCollide()){
      pieceR++; if(pieceR>=5){pieceR=1;}
    }
  }
  if(dcontrol==4){
    pieceCX--; //try and see what happens if we move the piece left
    if(checkCollide()){//piece move is not valid
      pieceCX++; //take piece back
    }
  }
  if(dcontrol==6){
    pieceCX++; //try and see what happens if we move the piece left
    if(checkCollide()){//piece move is not valid
      pieceCX--; //take piece back
    }
  }
  if(dcontrol==8){
    pieceCY--; //try and see what happens if we move the piece up
    if(checkCollide()){//piece move is not valid
      pieceCY++; //take piece back
    }
  }
  if(dcontrol==2||droppiece==1){
    pieceCY++; //try and see what happens if we move the piece down
    if(!(drepeatframe<=drepeatframes)){ //is in fast mode
      fdrop++;
    }else{
      fdrop=0;
    }
    if(checkCollide()){//piece move is not valid
      pieceCY--; //take piece back
      score+=fdrop; //add # of fast dropped blocks to score
      fdrop=0;
      piece2bg(); //copy piece to background and reset to next piece
    }
  }

  draw();
  dispscreen();
  
  clearControls();

  //check for line clears
  boolean clearline[pfsizeY];
  uint8_t clearedlines=0;
  uint8_t templines=0;
  for(uint8_t j=4; j<pfsizeY; j++){
  clearline[j]=1; //assume line is cleared
  for(uint8_t i=0; i<pfsizeX; i++){
    if(playfield[i][j]<=7){clearline[j]=0;break;} //line is not full
  }
  clearedlines+=clearline[j];
  templines+=clearline[j];
  }
  if(clearedlines>0){//breifly animate the cleared lines, then clear them
    for(uint8_t f=0; f<=6; f++){
      for(uint8_t j=4; j<pfsizeY; j++){
        if(clearline[j]==1){
          for(uint8_t i=0; i<pfsizeX; i++){
            if(f%2==0){playfield[i][j]=8;}else{playfield[i][j]=0;}
          }
        }
      }
      draw();
      dispscreen();
      delay(200);
    }
    for(uint8_t j=4; j<pfsizeY; j++){ //accutally clear the lines
       if(clearline[j]==1){
        for(uint8_t t=j; t>=4; t--){
         for(uint8_t i=0; i<pfsizeX; i++){
           playfield[i][t]=playfield[i][t-1];
         }
        }
       }
     }
   lines+=templines; //add number of lines to lines counter
   switch(templines){ //calculate score
    case 1:
      score+=40*(level+1);
      break;
    case 2:
      score+=100*(level+1);
      break;
    case 3:
      score+=300*(level+1);
      break;
    default:
      score+=1200*(level+1);
      break;
   }
   for(uint8_t i=1; i<=templines; i++){ //see if the level needs increasing
    lslvi++;
    if(lslvi>=10){lslvi=0;level++;}
    if(level>=20){level=20;}
   }
 }

  //check gameover (scan through line 3 and see if there are any non-active pieces in it)
  for(uint8_t i=0; i<pfsizeX; i++){
    if(playfield[i][3]>7){
      //*********************GAME OVER********************
      Serial.println(F("GAME OVER"));
      while(ngame==0){
        controls();
      }
      newgamemon();
    }
  }
  
  //check for completed lines

  
}