voxel-engine/src/World.cpp

#include "World.h"

#include <iostream>

// Helper function to handle negative modulo correctly
glm::ivec3 positive_modulo(glm::ivec3 value, int divisor) {
    glm::ivec3 result;
    result.x = ((value.x % divisor) + divisor) % divisor;
    result.y = ((value.y % divisor) + divisor) % divisor;
    result.z = ((value.z % divisor) + divisor) % divisor;
    return result;
}

// Helper function to correctly floor divide for chunk positions
glm::ivec3 floor_divide(glm::ivec3 value, int divisor) {
    glm::ivec3 result;
    result.x = (int)std::floor((float)value.x / divisor);
    result.y = (int)std::floor((float)value.y / divisor);
    result.z = (int)std::floor((float)value.z / divisor);
    return result;
}

World::World() {}

void World::set_voxel(glm::ivec3 position, VoxelKind kind) {
    glm::ivec3 chunk_position = floor_divide(position, CHUNK_SIZE);
    glm::ivec3 local_position = positive_modulo(position, CHUNK_SIZE);

    // std::cout << "[SET_VOXEL] World pos: (" << position.x << ", " << position.y << ", " << position.z << ")" << std::endl;
    // std::cout << "[SET_VOXEL] Chunk pos: (" << chunk_position.x << ", " << chunk_position.y << ", " << chunk_position.z << ")" << std::endl;
    // std::cout << "[SET_VOXEL] Local pos: (" << local_position.x << ", " << local_position.y << ", " << local_position.z << ")" << std::endl;

    Chunk * chunk = get_or_create_chunk(chunk_position);
    chunk->set(local_position, kind);

    chunk->regenerateMesh();
}

Chunk* World::get_or_create_chunk(glm::ivec3 chunk_position) {

    // Fill in new chunk with a flat plane of voxels at y=0
    auto [it, inserted] = this->chunks.try_emplace(chunk_position);
    Chunk& chunk = it->second;
    if (inserted) {
        if (chunk_position.y == 0) {
            for (int z = 0; z < CHUNK_SIZE; z++) {
                for (int y = 0; y < CHUNK_SIZE; y++) {
                    for (int x = 0; x < CHUNK_SIZE; x++) {
                        glm::ivec3 offset = glm::ivec3(x, y, z);
                        glm::ivec3 world_voxel_position = chunk_position * CHUNK_SIZE + offset;

                        VoxelKind kind;
                        if (world_voxel_position.y == 0) {
                            kind = VoxelKind::Dirt;
                        } else if (world_voxel_position.y < 0) {
                            kind = VoxelKind::Stone;
                        } else {
                            kind = VoxelKind::Air;
                        }

                        chunk.set(offset, kind);
                    }
                }
            }
        }
    }

    return &chunk;
}

std::optional<std::pair<glm::ivec3, glm::ivec3>> World::raycast_voxel(glm::vec3 start, glm::vec3 direction, float max_dist) {
    // Normalize direction to ensure consistent behavior
    direction = glm::normalize(direction);

    // std::cout << "[RAYCAST] Start: (" << start.x << ", " << start.y << ", " << start.z << ")" << std::endl;
    // std::cout << "[RAYCAST] Direction: (" << direction.x << ", " << direction.y << ", " << direction.z << ")" << std::endl;

    // Adjust start position to account for voxels being centered at integer + 0.5
    // (voxel at pos (0,0,0) occupies space from (-0.5,-0.5,-0.5) to (0.5,0.5,0.5))
    glm::vec3 adjusted_start = start + glm::vec3(0.5f, 0.5f, 0.5f);

    glm::ivec3 pos = glm::ivec3(std::floor(adjusted_start.x), std::floor(adjusted_start.y), std::floor(adjusted_start.z));
    // std::cout << "[RAYCAST] Starting voxel: (" << pos.x << ", " << pos.y << ", " << pos.z << ")" << std::endl;

    // (+1, -1, or 0 for each axis)
    glm::ivec3 step_dir = glm::ivec3(
        direction.x > 0 ? 1 : (direction.x < 0 ? -1 : 0),
        direction.y > 0 ? 1 : (direction.y < 0 ? -1 : 0),
        direction.z > 0 ? 1 : (direction.z < 0 ? -1 : 0)
    );
    // std::cout << "[RAYCAST] Step direction: (" << step_dir.x << ", " << step_dir.y << ", " << step_dir.z << ")" << std::endl;

    // Delta: how far along the ray we move for a full voxel step in each axis
    glm::vec3 delta = glm::vec3(
        step_dir.x != 0 ? std::abs(1.0f / direction.x) : FLT_MAX,
        step_dir.y != 0 ? std::abs(1.0f / direction.y) : FLT_MAX,
        step_dir.z != 0 ? std::abs(1.0f / direction.z) : FLT_MAX
    );

    // Calculate t_max: distance along ray to next voxel boundary for each axis
    glm::vec3 t_max;
    glm::vec3 fract = adjusted_start - glm::vec3(pos);

    // For each axis, calculate distance to the next boundary
    if (step_dir.x > 0)
        t_max.x = (1.0f - fract.x) * delta.x;
    else if (step_dir.x < 0)
        t_max.x = fract.x * delta.x;
    else
        t_max.x = FLT_MAX;

    if (step_dir.y > 0)
        t_max.y = (1.0f - fract.y) * delta.y;
    else if (step_dir.y < 0)
        t_max.y = fract.y * delta.y;
    else
        t_max.y = FLT_MAX;

    if (step_dir.z > 0)
        t_max.z = (1.0f - fract.z) * delta.z;
    else if (step_dir.z < 0)
        t_max.z = fract.z * delta.z;
    else
        t_max.z = FLT_MAX;

    float dist = 0.0f;
    glm::ivec3 last_move = glm::ivec3(0, 0, 0);

    int iterations = 0;
    const int max_iterations = 100; // Safety limit

    while (dist < max_dist && iterations < max_iterations) {
        iterations++;

        // std::cout << "[RAYCAST] Iteration " << iterations << " at voxel (" << pos.x << ", " << pos.y << ", " << pos.z << ")" << std::endl;

        if (this->get_voxel(pos) != VoxelKind::Air) {
            // std::cout << "[RAYCAST] Hit voxel at (" << pos.x << ", " << pos.y << ", " << pos.z << ") after " << iterations << " iterations" << std::endl;
            // std::cout << "[RAYCAST] Returning normal: (" << -last_move.x << ", " << -last_move.y << ", " << -last_move.z << ")" << std::endl;
            return std::make_pair(pos, -last_move);
        }

        // step in the axis with the smallest t_max - that's the next voxel boundary
        if (t_max.x < t_max.y && t_max.x < t_max.z) {
            pos.x += step_dir.x;
            last_move = glm::ivec3(step_dir.x, 0, 0);
            dist = t_max.x;
            t_max.x += delta.x;
        } else if (t_max.y < t_max.z) {
            pos.y += step_dir.y;
            last_move = glm::ivec3(0, step_dir.y, 0);
            dist = t_max.y;
            t_max.y += delta.y;
        } else {
            pos.z += step_dir.z;
            last_move = glm::ivec3(0, 0, step_dir.z);
            dist = t_max.z;
            t_max.z += delta.z;
        }
    }

    // std::cout << "[RAYCAST] No voxel hit after " << iterations << " iterations, dist=" << dist << std::endl;
    return std::nullopt;
}

VoxelKind World::get_voxel(glm::ivec3 position) {
    glm::ivec3 chunk_position = floor_divide(position, CHUNK_SIZE);
    glm::ivec3 local_position = positive_modulo(position, CHUNK_SIZE);

    Chunk* chunk = this->get_or_create_chunk(chunk_position);

    return chunk->get(position);
}