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

#include <math.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 char 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);

  rabbitBulletPosition[availableBullet].isActive = 1;
  rabbitBulletPosition[availableBullet].willBeInactive = 0;
  rabbitBulletPosition[availableBullet].x = rabbitPosition->rabbitPosition[0];
  rabbitBulletPosition[availableBullet].y = rabbitPosition->rabbitPosition[1] - RABBIT_BULLET_HEIGHT_START;
  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 % RABBIT_BULLET_VELOCITY;

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

  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() {
  int result;

  // first pass: are the hitboxes even close
  result = !(
    collisionDetection.sourceEY < collisionDetection.targetSY ||
    collisionDetection.sourceEX < collisionDetection.targetSX ||
    collisionDetection.targetEY < collisionDetection.sourceSY ||
    collisionDetection.targetEX < collisionDetection.sourceSX
  );

  if (!result) return result;

  // second pass: check against specific character shaped hitboxes
  // these will be generated from the spritesheet generator

  return result;
}

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;
}

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

  // to start: brute force items
  // possible performance improvements:
  // * horizontal sweep against enemies to rule out enemies to check
  for (bulletIdx = 0; bulletIdx < RABBIT_BULLET_LIMIT; ++bulletIdx) {
    if (!rabbitBulletPosition[bulletIdx].isActive) continue;
    if (rabbitBulletPosition[bulletIdx].willBeInactive) continue;

    populateSourceCollision(&bullet);

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

      populateTargetCollision(&enemy);

      if (isCollision()) {
        enemyPosition[enemyIdx].willBeInactive = 1;
        rabbitBulletPosition[bulletIdx].willBeInactive = 1;
        break;
      }
    }
  }
}