dos-vga-arena-shooter-game/combat.c

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#include "game.h"

#include "movement.h"
#include "const.h"
#include "system/vga.h"

void setupBullet(struct BulletPosition *bullet, int x, int y, signed int doubleVelocityX, signed int doubleVelocityY, int velocity) {
  bullet->isActive = 1;
  bullet->willBeInactive = 0;
  bullet->x = x;
  bullet->y = y;
  bullet->oldX = x;
  bullet->oldY = y;

  bullet->velocityXSteps[0] = doubleVelocityX / velocity;
  bullet->velocityXSteps[1] = doubleVelocityX - bullet->velocityXSteps[0];

  bullet->velocityYSteps[0] = doubleVelocityY / velocity;
  bullet->velocityYSteps[1] = doubleVelocityY - bullet->velocityYSteps[0];

  bullet->velocityStep = 0;
}

void attemptToFireRabbitBullet(
  struct RabbitPosition *rabbitPosition,
  struct RabbitWeaponry *rabbitWeaponry,
  struct BulletPosition rabbitBulletPosition[]
) {
  int okToFire = 0, availableBullet, i;
  signed int doubleVelocityX, doubleVelocityY;

  if (rabbitWeaponry->cooldown > 0) return;

  for (i = 0; i < RABBIT_BULLET_LIMIT; ++i) {
    if (rabbitBulletPosition[i].isActive == 0) {
      okToFire = 1;
      availableBullet = i;
      break;
    }
  }

  if (!okToFire) return;

  rabbitWeaponry->cooldown = RABBIT_BULLET_COOLDOWN;

  doubleVelocityX = sin(rabbitPosition->mouseAngle * DEG2RAD) * (RABBIT_BULLET_VELOCITY * 2);
  doubleVelocityY = -cos(rabbitPosition->mouseAngle * DEG2RAD) * (RABBIT_BULLET_VELOCITY * 2);

  setupBullet(
    &rabbitBulletPosition[availableBullet],
    rabbitPosition->rabbitPosition[0],
    rabbitPosition->rabbitPosition[1],
    doubleVelocityX,
    doubleVelocityY,
    RABBIT_BULLET_VELOCITY
  );
}

void advanceRabbitBullets(
  struct BulletPosition rabbitBulletPosition[],
  struct RabbitWeaponry *rabbitWeaponry
) {
  int i;

  for (i = 0; i < RABBIT_BULLET_LIMIT; ++i) {
    if (!rabbitBulletPosition[i].isActive) continue;

    rabbitBulletPosition[i].oldX = rabbitBulletPosition[i].x;
    rabbitBulletPosition[i].oldY = rabbitBulletPosition[i].y;

    rabbitBulletPosition[i].x += rabbitBulletPosition[i].velocityXSteps[rabbitBulletPosition[i].velocityStep];
    rabbitBulletPosition[i].y += rabbitBulletPosition[i].velocityYSteps[rabbitBulletPosition[i].velocityStep];

    if (rabbitBulletPosition[i].x < MOUSE_LIMIT_LEFT) rabbitBulletPosition[i].willBeInactive = 1;
    if (rabbitBulletPosition[i].x >= MOUSE_LIMIT_RIGHT) rabbitBulletPosition[i].willBeInactive = 1;
    if (rabbitBulletPosition[i].y < MOUSE_LIMIT_TOP) rabbitBulletPosition[i].willBeInactive = 1;
    if (rabbitBulletPosition[i].y >= MOUSE_LIMIT_BOTTOM) rabbitBulletPosition[i].willBeInactive = 1;

    rabbitBulletPosition[i].velocityStep = 1 - rabbitBulletPosition[i].velocityStep;
  }

  if (rabbitWeaponry->cooldown > 0) rabbitWeaponry->cooldown--;
}

void advanceEnemyBullets(
  struct BulletPosition enemyBulletPosition[]
) {
  int i;

  for (i = 0; i < ENEMY_BULLET_LIMIT; ++i) {
    if (!enemyBulletPosition[i].isActive) continue;

    enemyBulletPosition[i].oldX = enemyBulletPosition[i].x;
    enemyBulletPosition[i].oldY = enemyBulletPosition[i].y;

    enemyBulletPosition[i].x += enemyBulletPosition[i].velocityXSteps[enemyBulletPosition[i].velocityStep];
    enemyBulletPosition[i].y += enemyBulletPosition[i].velocityYSteps[enemyBulletPosition[i].velocityStep];

    if (enemyBulletPosition[i].x < MOUSE_LIMIT_LEFT) enemyBulletPosition[i].willBeInactive = 1;
    if (enemyBulletPosition[i].x >= MOUSE_LIMIT_RIGHT) enemyBulletPosition[i].willBeInactive = 1;
    if (enemyBulletPosition[i].y < MOUSE_LIMIT_TOP) enemyBulletPosition[i].willBeInactive = 1;
    if (enemyBulletPosition[i].y >= MOUSE_LIMIT_BOTTOM) enemyBulletPosition[i].willBeInactive = 1;

    enemyBulletPosition[i].velocityStep = 1 - enemyBulletPosition[i].velocityStep;
  }
}

void attemptToFireEnemyBullets(
  struct EnemyPosition enemyPosition[],
  struct BulletPosition enemyBulletPosition[],
  struct RabbitPosition *rabbitPosition
) {
  int availableBullets[ENEMY_BULLET_LIMIT];

  int i, availableBullet, maxAvailableBulletIndex = 0;
  float distanceX, distanceY, angle, doubleVelocityX, doubleVelocityY;

  for (i = 0; i < ENEMY_BULLET_LIMIT; ++i) {
    if (!enemyBulletPosition[i].isActive) {
      availableBullets[maxAvailableBulletIndex++] = i;
    }
  }

  for (i = 0; i < ENEMY_MAX_COUNT; ++i) {
    if (!enemyPosition[i].isActive) continue;

    enemyPosition[i].enemyFireDelayStep--;
    if (enemyPosition[i].enemyFireDelayStep > 0) continue;

    distanceX = rabbitPosition->rabbitPosition[0] - enemyPosition[i].enemyPosition[0];
    distanceY = rabbitPosition->rabbitPosition[1] - enemyPosition[i].enemyPosition[1];

    angle = atan2(distanceY, distanceX) * RAD2DEG + 90;
    if (angle < 0) angle += 360;

    doubleVelocityX = sin(angle * DEG2RAD) * (ENEMY_BULLET_VELOCITY * 2);
    doubleVelocityY = -cos(angle * DEG2RAD) * (ENEMY_BULLET_VELOCITY * 2);

    availableBullet = availableBullets[--maxAvailableBulletIndex];

    setupBullet(
      &enemyBulletPosition[availableBullet],
      enemyPosition[i].enemyPosition[0],
      enemyPosition[i].enemyPosition[1],
      doubleVelocityX,
      doubleVelocityY,
      ENEMY_BULLET_VELOCITY
    );

    enemyPosition[i].enemyFireDelayStep = ENEMY_FIRE_MIN_DELAY + rand() % ENEMY_FIRE_VARIABLE_DELAY;

    if (maxAvailableBulletIndex < 0) break;
  }
}

struct CollisionDetection {
  short int sourceSX, sourceSY, sourceEX, sourceEY;
  short int targetSX, targetSY, targetEX, targetEY;
};

struct CollisionDetection collisionDetection;

int isCollision() {
  if (collisionDetection.sourceEY < collisionDetection.targetSY) return 0;
  if (collisionDetection.sourceEX < collisionDetection.targetSX) return 0;
  if (collisionDetection.targetEY < collisionDetection.sourceSY) return 0;
  if (collisionDetection.targetEX < collisionDetection.sourceSX) return 0;

  return 1;
}

void populateSourceCollision(struct CompiledSpriteRender *sprite) {
  getSpriteBounds(sprite, &bounds);

  collisionDetection.sourceSX = bounds.left;
  collisionDetection.sourceSY = bounds.top;
  collisionDetection.sourceEX = bounds.right;
  collisionDetection.sourceEY = bounds.bottom;
}

void populateTargetCollision(struct CompiledSpriteRender *sprite) {
  getSpriteBounds(sprite, &bounds);

  collisionDetection.targetSX = bounds.left;
  collisionDetection.targetSY = bounds.top;
  collisionDetection.targetEX = bounds.right;
  collisionDetection.targetEY = bounds.bottom;
}

// We are hardcoding a 2x2 grid on the screen as our collision partitioning
// scheme.
int rabbitBulletGrid[4][RABBIT_BULLET_LIMIT];
int enemyGrid[4][ENEMY_MAX_COUNT];
int rabbitGrid[4];
int rabbitBulletGridIndex[4], enemyGridIndex[4];

int gridPosition[4];

#define CALCULATE_GRID_POS(x,y) ((x / COLLISION_GRID_SIZE) + (y / COLLISION_GRID_SIZE) * 2)

void determineGridPositionsForSprite(struct CompiledSpriteRender *sprite) {
  int i;

  getSpriteBounds(sprite, &bounds);

  for (i = 0; i < 4; ++i) {
    gridPosition[i] = 0;
  }

  gridPosition[CALCULATE_GRID_POS(bounds.left, bounds.top)] = 1;
  gridPosition[CALCULATE_GRID_POS(bounds.right, bounds.top)] = 1;
  gridPosition[CALCULATE_GRID_POS(bounds.left, bounds.bottom)] = 1;
  gridPosition[CALCULATE_GRID_POS(bounds.right, bounds.bottom)] = 1;
}

void buildCollisionGrids(
  struct BulletPosition rabbitBulletPosition[],
  struct RabbitPosition *rabbitPosition,
  struct EnemyPosition enemyPosition[]
) {
  int grid, i;

  for (grid = 0; grid < 4; ++grid) {
    rabbitBulletGridIndex[grid] = 0;
    enemyGridIndex[grid] = 0;
  }

  rabbit.x = rabbitPosition->rabbitPosition[0];
  rabbit.y = rabbitPosition->rabbitPosition[1];
  determineGridPositionsForSprite(&rabbit);

  for (grid = 0; grid < 4; ++grid) {
    rabbitGrid[grid] = gridPosition[grid];
  }

  for (i = 0; i < RABBIT_BULLET_LIMIT; ++i) {
    if (!rabbitBulletPosition[i].isActive) continue;
    if (rabbitBulletPosition[i].willBeInactive) continue;

    bullet.x = rabbitBulletPosition[i].x;
    bullet.y = rabbitBulletPosition[i].y;
    determineGridPositionsForSprite(&bullet);

    for (grid = 0; grid < 4; ++grid) {
      if (gridPosition[grid]) {
        rabbitBulletGrid[grid][rabbitBulletGridIndex[grid]++] = i;
      }
    }
  }

  for (i = 0; i < ENEMY_MAX_COUNT; ++i) {
    if (!enemyPosition[i].isActive) continue;
    if (enemyPosition[i].willBeInactive) continue;

    enemy.x = enemyPosition[i].enemyPosition[0];
    enemy.y = enemyPosition[i].enemyPosition[1];
    determineGridPositionsForSprite(&enemy);

    for (grid = 0; grid < 4; ++grid) {
      if (gridPosition[grid]) {
        enemyGrid[grid][enemyGridIndex[grid]++] = i;
      }
    }
  }
}

void handleRabbitBulletToEnemyCollisions(
  struct BulletPosition rabbitBulletPosition[],
  struct EnemyPosition enemyPosition[]
) {
  int bulletIdx, enemyIdx, grid;
  int resolvedBulletIdx, resolvedEnemyIdx;

  for (grid = 0; grid < 4; ++grid) {
    if (enemyGridIndex[grid] == 0) continue;

    for (bulletIdx = 0; bulletIdx < rabbitBulletGridIndex[grid]; ++bulletIdx) {
      resolvedBulletIdx = rabbitBulletGrid[grid][bulletIdx];

      if (!rabbitBulletPosition[resolvedBulletIdx].isActive) continue;
      if (rabbitBulletPosition[resolvedBulletIdx].willBeInactive) continue;

      bullet.x = rabbitBulletPosition[resolvedBulletIdx].x;
      bullet.y = rabbitBulletPosition[resolvedBulletIdx].y;
      populateSourceCollision(&bullet);

      for (enemyIdx = 0; enemyIdx < enemyGridIndex[grid]; ++enemyIdx) {
        resolvedEnemyIdx = enemyGrid[grid][enemyIdx];

        if (!enemyPosition[resolvedEnemyIdx].isActive) continue;
        if (enemyPosition[resolvedEnemyIdx].willBeInactive) continue;

        enemy.x = enemyPosition[resolvedEnemyIdx].enemyPosition[0];
        enemy.y = enemyPosition[resolvedEnemyIdx].enemyPosition[1];
        populateTargetCollision(&enemy);

        if (isCollision()) {
          enemyPosition[resolvedEnemyIdx].willBeInactive = 1;
          enemyPosition[resolvedBulletIdx].wasKilled = 1;
          rabbitBulletPosition[resolvedBulletIdx].willBeInactive = 1;
          break;
        }
      }
    }
  }
}

void handleRabbitToEnemyCollisions(
  struct RabbitPosition *rabbitPosition,
  struct EnemyPosition enemyPosition[]
) {
  int enemyIdx, grid, resolvedEnemyIdx;

  // to start: brute force items
  // possible performance improvements:
  // * grid partitioning
  rabbit.x = rabbitPosition->rabbitPosition[0];
  rabbit.y = rabbitPosition->rabbitPosition[1];
  populateSourceCollision(&rabbit);

  for (grid = 0; grid < 4; ++grid) {
    if (!rabbitGrid[grid]) continue;
    if (enemyGridIndex[grid] == 0) continue;

    for (enemyIdx = 0; enemyIdx < enemyGridIndex[grid]; ++enemyIdx) {
      resolvedEnemyIdx = enemyGrid[grid][enemyIdx];

      if (!enemyPosition[resolvedEnemyIdx].isActive) continue;
      if (enemyPosition[resolvedEnemyIdx].willBeInactive) continue;

      enemy.x = enemyPosition[resolvedEnemyIdx].enemyPosition[0];
      enemy.y = enemyPosition[resolvedEnemyIdx].enemyPosition[1];
      populateTargetCollision(&enemy);

      if (isCollision()) {
        enemyPosition[resolvedEnemyIdx].willBeInactive = 1;
      }
    }
  }
}