Move OpenGL backend classes from tests/OpenGL to engine/

- Relocated OpenGLDevice, OpenGLShader, OpenGLBuffer, OpenGLVertexArray, OpenGLTexture to engine/
- Updated engine/CMakeLists.txt to include OpenGL backend source files
- Updated tests/OpenGL/CMakeLists.txt to use engine backend
- Added OpenGLTexture class implementation

engine/src/RHI/OpenGL/OpenGLTexture.cpp

@@ -0,0 +1,79 @@
+#define GLFW_INCLUDE_NONE
+#include "XCEngine/RHI/OpenGL/OpenGLTexture.h"
+#include <glad/glad.h>
+#include <GLFW/glfw3.h>
+#include <stb_image.h>
+#include <iostream>
+
+namespace XCEngine {
+namespace RHI {
+
+OpenGLTexture::OpenGLTexture()
+    : m_texture(0)
+    , m_width(0)
+    , m_height(0)
+    , m_channels(0) {
+}
+
+OpenGLTexture::~OpenGLTexture() {
+    Shutdown();
+}
+
+bool OpenGLTexture::Initialize2D(int width, int height, int channels, const void* data, bool generateMipmap) {
+    glGenTextures(1, &m_texture);
+    glBindTexture(GL_TEXTURE_2D, m_texture);
+    
+    GLenum format = (channels == 4) ? GL_RGBA : GL_RGB;
+    glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
+    
+    if (generateMipmap) {
+        glGenerateMipmap(GL_TEXTURE_2D);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+    } else {
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    }
+    
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+    
+    m_width = width;
+    m_height = height;
+    m_channels = channels;
+    
+    glBindTexture(GL_TEXTURE_2D, 0);
+    return true;
+}
+
+bool OpenGLTexture::LoadFromFile(const char* path, bool flipVertical) {
+    stbi_set_flip_vertically_on_load(flipVertical ? 1 : 0);
+    
+    unsigned char* data = stbi_load(path, &m_width, &m_height, &m_channels, 0);
+    if (!data) {
+        std::cout << "Failed to load texture: " << path << std::endl;
+        return false;
+    }
+    
+    bool result = Initialize2D(m_width, m_height, m_channels, data, true);
+    stbi_image_free(data);
+    return result;
+}
+
+void OpenGLTexture::Shutdown() {
+    if (m_texture) {
+        glDeleteTextures(1, &m_texture);
+        m_texture = 0;
+    }
+}
+
+void OpenGLTexture::Bind(int slot) const {
+    glActiveTexture(GL_TEXTURE0 + slot);
+    glBindTexture(GL_TEXTURE_2D, m_texture);
+}
+
+void OpenGLTexture::Unbind() const {
+    glBindTexture(GL_TEXTURE_2D, 0);
+}
+
+} // namespace RHI
+} // namespace XCEngine