Add OpenGL backend infrastructure for cross-platform EGE support

CMakeLists.txt

@@ -24,6 +24,9 @@ option(EGE_BUILD_DEMO "Build ege demos" ${EGE_IS_ROOT_PROJECT})
 option(EGE_BUILD_TEST "Build ege tests" ${EGE_IS_ROOT_PROJECT})
 option(EGE_BUILD_TEMP "Build ege temp" ${EGE_IS_ROOT_PROJECT})
 
+# OpenGL backend option - experimental cross-platform support
+option(EGE_ENABLE_OPENGL "Enable OpenGL rendering backend (experimental)" OFF)
+
 # EGE_DISABLE_DEBUG_INFO 选项：禁用调试信息，避免 LNK4099 警告
 # 优先使用 CMake 参数，其次检查环境变量，默认 OFF
 if(NOT DEFINED EGE_DISABLE_DEBUG_INFO)
@@ -47,6 +50,7 @@ message(STATUS "EGE_CLEAR_OPTIONS_CACHE: ${EGE_CLEAR_OPTIONS_CACHE}")
 message(STATUS "EGE_BUILD_DEMO:  ${EGE_BUILD_DEMO}")
 message(STATUS "EGE_BUILD_TEST:  ${EGE_BUILD_TEST}")
 message(STATUS "EGE_BUILD_TEMP:  ${EGE_BUILD_TEMP}")
+message(STATUS "EGE_ENABLE_OPENGL: ${EGE_ENABLE_OPENGL}")
 message(STATUS "EGE_DISABLE_DEBUG_INFO: ${EGE_DISABLE_DEBUG_INFO}")
 
 if(CMAKE_HOST_UNIX)
@@ -129,8 +133,13 @@ if(EGE_ENABLE_CPP17)
     set(CMAKE_CXX_EXTENSIONS OFF)
 endif()
 
+# Collect source files from src/ directory
 file(GLOB EGE_CPP_SRC CONFIGURE_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/src/*.cpp)
-add_library(xege STATIC ${EGE_CPP_SRC})
+
+# Collect backend source files
+file(GLOB EGE_BACKEND_SRC CONFIGURE_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/src/backend/*.cpp)
+
+add_library(xege STATIC ${EGE_CPP_SRC} ${EGE_BACKEND_SRC})
 
 target_include_directories(xege PUBLIC include)
 
@@ -223,6 +232,77 @@ else()
     message(WARNING "Camera capture is disabled because your compiler does not support C++17.")
 endif()
 
+# OpenGL backend configuration (experimental cross-platform support)
+if(EGE_ENABLE_OPENGL)
+    message(STATUS "OpenGL backend enabled (experimental)")
+
+    # Find OpenGL
+    find_package(OpenGL REQUIRED)
+
+    # Check for GLFW
+    find_package(glfw3 CONFIG QUIET)
+    if(NOT glfw3_FOUND)
+        # Try to find GLFW via pkg-config
+        find_package(PkgConfig QUIET)
+        if(PKG_CONFIG_FOUND)
+            pkg_check_modules(GLFW3 glfw3)
+        endif()
+
+        if(NOT GLFW3_FOUND)
+            message(STATUS "GLFW3 not found in system, checking 3rdparty...")
+            # Check if GLFW is available in 3rdparty
+            if(EXISTS "${PROJECT_SOURCE_DIR}/3rdparty/glfw/CMakeLists.txt")
+                set(GLFW_BUILD_DOCS OFF CACHE BOOL "" FORCE)
+                set(GLFW_BUILD_TESTS OFF CACHE BOOL "" FORCE)
+                set(GLFW_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
+                add_subdirectory(${PROJECT_SOURCE_DIR}/3rdparty/glfw)
+                set(GLFW_LIBRARIES glfw)
+                set(GLFW_INCLUDE_DIRS ${PROJECT_SOURCE_DIR}/3rdparty/glfw/include)
+            else()
+                message(WARNING "GLFW not found. OpenGL backend disabled.")
+                message(WARNING "To enable, install GLFW or add it as a submodule in 3rdparty/glfw")
+                set(EGE_ENABLE_OPENGL OFF)
+            endif()
+        else()
+            set(GLFW_LIBRARIES ${GLFW3_LIBRARIES})
+            set(GLFW_INCLUDE_DIRS ${GLFW3_INCLUDE_DIRS})
+        endif()
+    else()
+        set(GLFW_LIBRARIES glfw)
+    endif()
+
+    # Check for GLAD
+    if(EGE_ENABLE_OPENGL)
+        if(EXISTS "${PROJECT_SOURCE_DIR}/3rdparty/glad/include/glad/glad.h")
+            set(GLAD_INCLUDE_DIRS ${PROJECT_SOURCE_DIR}/3rdparty/glad/include)
+            # Add GLAD source file if it exists
+            if(EXISTS "${PROJECT_SOURCE_DIR}/3rdparty/glad/src/glad.c")
+                target_sources(xege PRIVATE ${PROJECT_SOURCE_DIR}/3rdparty/glad/src/glad.c)
+            endif()
+        else()
+            message(WARNING "GLAD not found in 3rdparty/glad. OpenGL backend disabled.")
+            message(WARNING "To enable, add GLAD to 3rdparty/glad with include/glad/glad.h")
+            set(EGE_ENABLE_OPENGL OFF)
+        endif()
+    endif()
+
+    # Apply OpenGL configuration if still enabled
+    if(EGE_ENABLE_OPENGL)
+        target_compile_definitions(xege PRIVATE EGE_ENABLE_OPENGL=1)
+        target_include_directories(xege PRIVATE ${GLFW_INCLUDE_DIRS})
+        if(DEFINED GLAD_INCLUDE_DIRS)
+            target_include_directories(xege PRIVATE ${GLAD_INCLUDE_DIRS})
+        endif()
+        target_link_libraries(xege INTERFACE OpenGL::GL)
+        if(DEFINED GLFW_LIBRARIES)
+            target_link_libraries(xege INTERFACE ${GLFW_LIBRARIES})
+        endif()
+        message(STATUS "OpenGL backend configured successfully")
+    endif()
+else()
+    message(STATUS "OpenGL backend disabled (use -DEGE_ENABLE_OPENGL=ON to enable)")
+endif()
+
 # 设置库文件名
 # MSVC 下 Debug 版本使用 graphicsd.lib，Release 版本使用 graphics.lib
 # MinGW 不区分 Debug/Release，统一使用 graphics

demo/graph_opengl_test.cpp

@@ -0,0 +1,89 @@
+/*
+ * EGE (Easy Graphics Engine)
+ * Demo: graph_opengl_test.cpp
+ *
+ * This demo demonstrates the usage of the OpenGL rendering backend.
+ * It draws basic shapes using the same EGE API that works with both
+ * GDI and OpenGL backends.
+ *
+ * To enable OpenGL backend:
+ * 1. Build EGE with -DEGE_ENABLE_OPENGL=ON
+ * 2. Use INIT_OPENGL flag: initgraph(640, 480, INIT_OPENGL);
+ *
+ * Note: This is an experimental feature for cross-platform support.
+ * The OpenGL backend currently supports basic drawing operations.
+ */
+
+#include <ege.h>
+
+int main()
+{
+    // Initialize with OpenGL backend (experimental)
+    // If OpenGL backend is not available, falls back to GDI
+#ifdef EGE_ENABLE_OPENGL
+    ege::initgraph(640, 480, ege::INIT_OPENGL | ege::INIT_RENDERMANUAL);
+    ege::setcaption("EGE OpenGL Backend Demo");
+#else
+    ege::initgraph(640, 480, ege::INIT_RENDERMANUAL);
+    ege::setcaption("EGE Demo (GDI Backend)");
+#endif
+
+    // Set background color
+    ege::setbkcolor(ege::EGERGB(32, 32, 48));
+    ege::cleardevice();
+
+    // Draw some shapes to demonstrate rendering
+    // These functions work with both GDI and OpenGL backends
+
+    // Draw a circle
+    ege::setcolor(ege::EGERGB(255, 100, 100));
+    ege::circle(160, 160, 80);
+
+    // Draw a filled circle
+    ege::setfillcolor(ege::EGERGB(100, 255, 100));
+    ege::fillellipse(320, 160, 80, 80);
+
+    // Draw a rectangle outline
+    ege::setcolor(ege::EGERGB(100, 100, 255));
+    ege::rectangle(420, 80, 580, 240);
+
+    // Draw a filled rectangle
+    ege::setfillcolor(ege::EGERGB(255, 255, 100));
+    ege::bar(80, 280, 200, 400);
+
+    // Draw some lines
+    ege::setcolor(ege::EGERGB(255, 128, 0));
+    for (int i = 0; i < 10; i++) {
+        ege::line(240, 280 + i * 12, 560, 280 + i * 12);
+    }
+
+    // Draw an ellipse
+    ege::setcolor(ege::EGERGB(255, 0, 255));
+    ege::ellipse(400, 360, 0, 360, 120, 60);
+
+    // Draw filled ellipse
+    ege::setfillcolor(ege::EGERGB(0, 255, 255));
+    ege::fillellipse(160, 360, 60, 40);
+
+    // Draw some text
+    ege::setcolor(ege::WHITE);
+    ege::outtextxy(10, 10, "EGE Cross-Platform Backend Demo");
+    ege::outtextxy(10, 30, "Press any key to exit...");
+
+#ifdef EGE_ENABLE_OPENGL
+    ege::outtextxy(10, 450, "Backend: OpenGL (experimental)");
+#else
+    ege::outtextxy(10, 450, "Backend: GDI (default)");
+#endif
+
+    // Update the display
+    ege::flushwindow();
+
+    // Wait for user input
+    ege::getch();
+
+    // Close graphics
+    ege::closegraph();
+
+    return 0;
+}

docs/CROSS_PLATFORM.md

@@ -0,0 +1,122 @@
+# EGE 跨平台支持 / Cross-Platform Support
+
+## 概述 / Overview
+
+EGE 现在支持多渲染后端架构，允许在保持向后兼容的同时，支持跨平台渲染。
+
+EGE now supports a multi-backend rendering architecture, allowing cross-platform rendering while maintaining backward compatibility.
+
+## 渲染后端 / Rendering Backends
+
+### GDI 后端 (默认) / GDI Backend (Default)
+
+- **平台 / Platform**: Windows only
+- **状态 / Status**: 稳定 / Stable
+- **说明 / Description**: 使用 Windows GDI/GDI+ 进行渲染，这是 EGE 的原始实现。
+
+### OpenGL 后端 (实验性) / OpenGL Backend (Experimental)
+
+- **平台 / Platform**: Windows, macOS, Linux
+- **状态 / Status**: 实验性 / Experimental
+- **说明 / Description**: 使用 OpenGL 进行渲染，通过 GLFW 管理窗口，实现真正的跨平台支持。
+
+## 使用方法 / Usage
+
+### 编译时启用 OpenGL / Enable OpenGL at Build Time
+
+```bash
+# CMake 配置时启用 OpenGL 后端
+cmake .. -DEGE_ENABLE_OPENGL=ON
+```
+
+### 运行时选择后端 / Select Backend at Runtime
+
+```cpp
+#include <ege.h>
+
+int main() {
+    // 使用默认 GDI 后端 / Use default GDI backend
+    ege::initgraph(640, 480, ege::INIT_DEFAULT);
+
+    // 或使用 OpenGL 后端 / Or use OpenGL backend
+    ege::initgraph(640, 480, ege::INIT_OPENGL);
+
+    // ... 绑定代码相同 / binding code is the same
+}
+```
+
+## 后端抽象层 / Backend Abstraction Layer
+
+### 目录结构 / Directory Structure
+
+```
+src/
+└── backend/
+    ├── render_backend.h      # 抽象接口 / Abstract interface
+    ├── render_backend.cpp    # 后端工厂 / Backend factory
+    ├── gdi_backend.h         # GDI 后端头文件
+    ├── gdi_backend.cpp       # GDI 后端实现
+    ├── opengl_backend.h      # OpenGL 后端头文件
+    └── opengl_backend.cpp    # OpenGL 后端实现
+```
+
+### RenderBackend 接口 / Interface
+
+所有渲染后端都实现 `RenderBackend` 接口，提供以下功能：
+
+All rendering backends implement the `RenderBackend` interface, providing:
+
+- 初始化和关闭 / Initialization and shutdown
+- 缓冲区交换 / Buffer swapping
+- 清屏 / Clear screen
+- 像素操作 / Pixel operations
+- 基本图形绘制（线、矩形、圆、椭圆）/ Basic shape drawing (line, rectangle, circle, ellipse)
+- 事件处理 / Event processing
+
+## 依赖 / Dependencies
+
+### OpenGL 后端依赖 / OpenGL Backend Dependencies
+
+- **GLFW**: 窗口管理 / Window management
+- **GLAD**: OpenGL 加载器 / OpenGL loader
+
+这些依赖可以通过以下方式添加 / These dependencies can be added via:
+
+1. 系统包管理器 / System package manager
+2. Git 子模块到 `3rdparty/` / Git submodules to `3rdparty/`
+
+## 已知限制 / Known Limitations
+
+OpenGL 后端目前处于实验阶段，以下功能可能不完全支持：
+
+The OpenGL backend is currently experimental, the following features may not be fully supported:
+
+1. 文字渲染 / Text rendering
+2. 图像操作 / Image operations
+3. 部分高级 GDI+ 功能 / Some advanced GDI+ features
+
+## 路线图 / Roadmap
+
+1. **阶段 1** (已完成): 添加 `INIT_OPENGL` 标志和后端抽象层
+2. **阶段 2**: 集成 GLFW 和 GLAD
+3. **阶段 3**: 实现基本绘图功能的 OpenGL 版本
+4. **阶段 4**: 添加文字渲染支持
+5. **阶段 5**: 添加图像操作支持
+
+---
+
+## 开发者指南 / Developer Guide
+
+### 添加新后端 / Adding a New Backend
+
+1. 在 `src/backend/` 创建新的后端类
+2. 继承 `RenderBackend` 接口
+3. 实现所有虚函数
+4. 在 `render_backend.cpp` 中注册后端
+5. 更新 CMakeLists.txt 添加条件编译
+
+### 测试后端 / Testing a Backend
+
+使用 `demo/graph_opengl_test.cpp` 作为测试参考。
+
+Use `demo/graph_opengl_test.cpp` as a testing reference.

include/ege.h

@@ -238,6 +238,7 @@ enum initmode_flag
     INIT_UNICODE         = 0x20,  ///< Unicode character messages (equivalent to setunicodecharmessage(true))
     INIT_HIDE            = 0x40,  ///< Hidden window
     INIT_WITHLOGO        = 0x100, ///< Show EGE Logo animation on startup (not shown by default in Debug version)
+    INIT_OPENGL          = 0x200, ///< Use OpenGL rendering backend (experimental, for cross-platform support)
     INIT_ANIMATION       = INIT_DEFAULT | INIT_RENDERMANUAL | INIT_NOFORCEEXIT ///< Animation mode
 };
 

include/ege.zh_CN.h

@@ -238,6 +238,7 @@ enum initmode_flag
     INIT_UNICODE         = 0x20,  ///< Unicode字符消息 (等同于setunicodecharmessage(true))
     INIT_HIDE            = 0x40,  ///< 隐藏窗口
     INIT_WITHLOGO        = 0x100, ///< 启动时显示EGE Logo 动画 (Debug版本下默认不显示)
+    INIT_OPENGL          = 0x200, ///< 使用OpenGL渲染后端 (实验性功能，用于跨平台支持)
     INIT_ANIMATION       = INIT_DEFAULT | INIT_RENDERMANUAL | INIT_NOFORCEEXIT ///< 动画模式
 };