school_stm32/game_engine/ecs/ge_collision_system.h

#ifndef __GE_COLLISION_SYSTEM_H__
#define __GE_COLLISION_SYSTEM_H__ 

#include "ge_entity.h"
#include "ge_collision_component.h"
#include <utils/ge_vector2i.h>
#include <utils/ge_maroc.h>
#include <pynic_log/pynic_log.h>


typedef void (*ge_collision_response_func_t)(
    void* ctx,
    ge_entity_t* entity_from, 
    ge_entity_t* entity_to,
    const ge_vector2i_t* vector // 反向推荐速度
);

typedef struct ge_collision_system {
    ge_ecs_storage_t* ecs;
    void* ctx;
    ge_collision_response_func_t callback;
} ge_collision_system_t;

#define _GE_COLLIDER_MASK (GE_COLLIDER_MASK | GE_COMPONENT_ACVIVE)

/**
 * must transit to global position before calling this function
 */
static inline int check_box_collision(ge_collision_box_t* a, ge_collision_box_t* b) {
    return (a->relative_pos.x < b->relative_pos.x + b->size.x) &&
           (a->relative_pos.x + a->size.x > b->relative_pos.x) &&
           (a->relative_pos.y < b->relative_pos.y + b->size.y) &&
           (a->relative_pos.y + a->size.y > b->relative_pos.y);
}

static inline ge_vector2i_t check_tilemap_collision(
    ge_collision_box_t* entity_collision,
    ge_vector2i_t* entity_pos,
    ge_collision_tilemap_t* tilemap,
    ge_vector2i_t* tilemap_pos
) {
    Assert(tilemap->tile_size > 0);
    Assert(tilemap->map_size.x > 0 && tilemap->map_size.y > 0);
    Assert(entity_collision->size.x > 0 && entity_collision->size.y > 0);

    const ge_unit_t tile_size_int = tilemap->tile_size;
    const ge_unit_t grid_cols = tilemap->map_size.x;
    const ge_unit_t grid_rows = tilemap->map_size.y;

    // 计算实体碰撞盒在瓦片地图局部坐标系中的位置
    const ge_vector2i_t local_entity_pos = GE_VEC2I_SUB(
        *entity_pos,
        *tilemap_pos
    );

    // 计算实体边界（闭区间）
    const int entity_left = local_entity_pos.x;
    const int entity_top = local_entity_pos.y;
    const int entity_right = entity_left + entity_collision->size.x;
    const int entity_bottom = entity_top + entity_collision->size.y;

    // 计算覆盖的瓦片范围
    const int start_tile_x = GE_MAX(0, entity_left / tile_size_int);
    const int start_tile_y = GE_MAX(0, entity_top / tile_size_int);
    const int end_tile_x = GE_MIN(grid_cols - 1, entity_right / tile_size_int);
    const int end_tile_y = GE_MIN(grid_rows - 1, entity_bottom / tile_size_int);

    ge_vector2i_t correction = GE_VEC2I(0, 0); // 默认无纠正
    
    for (int y = start_tile_y; y <= end_tile_y; y++) {
        for (int x = start_tile_x; x <= end_tile_x; x++) {
            if (tilemap->layers[y * grid_cols + x] == 0) continue;

            // 计算当前瓦片的边界
            const int tile_left = x * tile_size_int;
            const int tile_top = y * tile_size_int;
            const int tile_right = tile_left + tile_size_int;
            const int tile_bottom = tile_top + tile_size_int;

            // 检查实体是否实际接触到瓦片内部
            const int overlap_x = entity_left < tile_right && entity_right > tile_left;
            const int overlap_y = entity_top < tile_bottom && entity_bottom > tile_top;

            if (overlap_x && overlap_y) {
                // 计算重叠区域
                const int overlap_left = GE_MAX(entity_left, tile_left);
                const int overlap_right = GE_MIN(entity_right, tile_right);
                const int overlap_top = GE_MAX(entity_top, tile_top);
                const int overlap_bottom = GE_MIN(entity_bottom, tile_bottom);
                
                const int overlap_width = overlap_right - overlap_left;
                const int overlap_height = overlap_bottom - overlap_top;
                
                // 计算实体中心到瓦片中心的向量
                const int entity_center_x = (entity_left + entity_right) / 2;
                const int entity_center_y = (entity_top + entity_bottom) / 2;
                const int tile_center_x = (tile_left + tile_right) / 2;
                const int tile_center_y = (tile_top + tile_bottom) / 2;
                
                const int dx = entity_center_x - tile_center_x;
                const int dy = entity_center_y - tile_center_y;
                
                // 确定主要分离方向（选择重叠量较小的轴）
                if (overlap_width < overlap_height) {
                    // X轴方向分离（左右方向）
                    correction.x = (dx > 0) ? overlap_width : -overlap_width;
                } else {
                    // Y轴方向分离（上下方向）
                    correction.y = (dy > 0) ? overlap_height : -overlap_height;
                }
                
                // 返回第一个找到的碰撞纠正（最大影响）
                return correction;
            }
        }
    }

    return correction; // 无碰撞时返回零向量
}

// FIXME bad practice
static inline void
ge_collision_system_run_all(ge_collision_system_t* ctx) {
    Assert(ctx != NULL);
    if (ctx->callback == NULL) return;
    ge_ecs_storage_t* ecs = ctx->ecs;
    Assert(ecs != NULL);
    for (int i = 1; i <= ecs->count && i < GE_ECS_MAX; ++i) {
        ge_entity_t* entity_i = &ecs->entities[i];
        ge_ecs_mask_t mask_i = entity_i->component_mask;
        if ((mask_i & _GE_COLLIDER_MASK) != _GE_COLLIDER_MASK) continue;
        ge_collision_component_t* comp_i = &entity_i->collision;
        Assert(comp_i != NULL);
        // FIXME this design is bad
        /**
         * 仅仅尝试 (box, box) 和 (box, tilemap) 的碰撞
         */
        if (comp_i->type != GE_COLLISION_COMP_TYPE_BOX) continue;

        for (int j = 1; j <= ecs->count && j < GE_ECS_MAX; ++j) {
            if (i == j) continue;
            ge_entity_t* entity_j = &ecs->entities[j];
            ge_ecs_mask_t mask_j = entity_j->component_mask;
            if ((mask_j & _GE_COLLIDER_MASK) != _GE_COLLIDER_MASK) continue;
            ge_collision_component_t* comp_j = &entity_j->collision;
            Assert(comp_j != NULL);

            /**
             * using layer/mask to accelerate check
             */
            if ( !(comp_i->mask & comp_j->layers) ) {
                continue;
            }

            /**
             * Check collision
             */
            switch (comp_j->type) {
                case GE_COLLISION_COMP_TYPE_BOX: {
                    int ret = check_box_collision(&comp_i->collider.box, &comp_j->collider.box);
                    if (!ret) ctx->callback(ctx->ctx, entity_i, entity_j, NULL);
                    break;
                }
                case GE_COLLISION_COMP_TYPE_TILEMAP: {
                    ge_vector2i_t ret = check_tilemap_collision(
                        &comp_i->collider.box,
                        &entity_i->position,
                        &comp_j->collider.tilemap,
                        &entity_j->position
                    );

                    if (ret.x == 0 && ret.y == 0) {
                        continue;
                    }
                    ctx->callback(ctx->ctx, entity_i, entity_j, &ret);
                    break;
                }
                default:
                    LOG_WARN("Collision system: Unknown collision type");
                    break;
            }
        }
    }
}

#endif /* __GE_COLLISION_SYSTEM_H__ */