Skybox.cpp

#include "Skybox.h"
#include "stb_image.h"
#include <glm/gtc/type_ptr.hpp>
#include <iostream>

using namespace std;
using namespace glm;

// Cube vertices — just positions, no UVs needed
static float skyboxVertices[] = {
    -1.f, -1.f,  1.f,  // 0
     1.f, -1.f,  1.f,  // 1
     1.f, -1.f, -1.f,  // 2
    -1.f, -1.f, -1.f,  // 3
    -1.f,  1.f,  1.f,  // 4
     1.f,  1.f,  1.f,  // 5
     1.f,  1.f, -1.f,  // 6
    -1.f,  1.f, -1.f   // 7
};

static unsigned int skyboxIndices[] = {
    1,2,6,  6,5,1,   // right
    0,4,7,  7,3,0,   // left
    4,5,6,  6,7,4,   // top
    0,3,2,  2,1,0,   // bottom
    0,1,5,  5,4,0,   // front
    3,7,6,  6,2,3    // back
};

// ---- Load 6 faces into a cubemap texture ----
void Skybox::loadCubemap(const string faces[6]) {
    glGenTextures(1, &cubemapTexture);
    glBindTexture(GL_TEXTURE_CUBE_MAP, cubemapTexture);

    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    stbi_set_flip_vertically_on_load(false);

    for (unsigned int i = 0; i < 6; i++) {
        int w, h, ch;
        unsigned char* data = stbi_load(faces[i].c_str(), &w, &h, &ch, 0);
        if (data) {
            GLenum fmt = (ch == 4) ? GL_RGBA : GL_RGB;
            glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i,
                         0, fmt, w, h, 0, fmt, GL_UNSIGNED_BYTE, data);
            stbi_image_free(data);
            cout << "[Skybox] Loaded face " << i << ": " << faces[i] << endl;
        } else {
            cerr << "[Skybox] Failed to load face: " << faces[i] << endl;
            cerr << "  STB: " << stbi_failure_reason() << endl;
        }
    }

    stbi_set_flip_vertically_on_load(true);
}

// ---- Setup VAO/VBO/EBO ----
void Skybox::setupMesh() {
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(skyboxVertices),
                 skyboxVertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(skyboxIndices),
                 skyboxIndices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE,
                          3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    glBindVertexArray(0);
}

// ---- Constructor ----
Skybox::Skybox(const string faces[6]) {
    setupMesh();
    loadCubemap(faces);
}

// ---- Destructor ----
Skybox::~Skybox() {
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);
    glDeleteTextures(1, &cubemapTexture);
}

// ---- Draw ----
void Skybox::draw(Shader& skyboxShader, mat4 view, mat4 projection) {
    // Draw skybox first, disable depth writing
    glDepthMask(GL_FALSE);
    glDepthFunc(GL_LEQUAL);

    skyboxShader.use();

    // Strip translation from view matrix so skybox stays fixed
    mat4 skyView = mat4(mat3(view));
    skyboxShader.setMat4("view",       value_ptr(skyView));
    skyboxShader.setMat4("projection", value_ptr(projection));

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_CUBE_MAP, cubemapTexture);
    skyboxShader.setInt("skybox", 0);

    glBindVertexArray(VAO);
    glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_INT, 0);
    glBindVertexArray(0);

    // Restore depth state
    glDepthMask(GL_TRUE);
    glDepthFunc(GL_LESS);
}