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

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

#include "game.h"

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

void attemptToFireRabbitBullet(
  struct RabbitPosition *rabbitPosition,
  struct RabbitWeaponry *rabbitWeaponry,
  struct BulletPosition rabbitBulletPosition[]
) {
  int okToFire = 0, availableBullet, i;
  signed int doubleVelocityX, doubleVelocityY;
  char buffer[20];

  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);

  rabbitBulletPosition[availableBullet].isActive = 1;
  rabbitBulletPosition[availableBullet].willBeInactive = 0;
  rabbitBulletPosition[availableBullet].x = rabbitPosition->rabbitPosition[0];
  rabbitBulletPosition[availableBullet].y = rabbitPosition->rabbitPosition[1];
  rabbitBulletPosition[availableBullet].oldX = rabbitBulletPosition[availableBullet].x;
  rabbitBulletPosition[availableBullet].oldY = rabbitBulletPosition[availableBullet].y;

  rabbitBulletPosition[availableBullet].velocityXSteps[0] = doubleVelocityX / RABBIT_BULLET_VELOCITY;
  rabbitBulletPosition[availableBullet].velocityXSteps[1] = doubleVelocityX - rabbitBulletPosition[availableBullet].velocityXSteps[0];

  rabbitBulletPosition[availableBullet].velocityYSteps[0] = doubleVelocityY / RABBIT_BULLET_VELOCITY;
  rabbitBulletPosition[availableBullet].velocityYSteps[1] = doubleVelocityY - rabbitBulletPosition[availableBullet].velocityYSteps[0];

  rabbitBulletPosition[availableBullet].velocityStep = 0;
}

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--;
}

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;
          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;
      }
    }
  }
}