docs: update math API docs

docs/api/math/viewport/getaspectratio.md

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+# Viewport::GetAspectRatio
+
+```cpp
+float GetAspectRatio() const;
+```
+
+获取视口宽高比。
+
+**返回：** 宽高比 (width / height)，如果 height 为 0 则返回 0.0f
+
+**线程安全：** ✅
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+#include "XCEngine/Math/Rect.h"
+#include <iostream>
+
+using namespace XCEngine::Math;
+
+int main() {
+    Viewport viewport(0.0f, 0.0f, 1920.0f, 1080.0f);
+    float aspect = viewport.GetAspectRatio();
+    std::cout << "Aspect Ratio: " << aspect << "\n";
+    return 0;
+}
+```
+
+## 相关文档
+
+- [`Viewport::GetRect`](getrect.md) - 转换为 Rect
+- [Viewport 总览](viewport.md)

docs/api/math/viewport/getrect.md

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+# Viewport::GetRect
+
+```cpp
+Rect GetRect() const;
+```
+
+将视口转换为 Rect。
+
+**返回：** 对应的 Rect（x, y, width, height），不包含深度范围
+
+**线程安全：** ✅
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+#include "XCEngine/Math/Rect.h"
+#include <iostream>
+
+using namespace XCEngine::Math;
+
+int main() {
+    Viewport viewport(0.0f, 0.0f, 1920.0f, 1080.0f, 0.0f, 1.0f);
+    Rect rect = viewport.GetRect();
+    std::cout << "Rect: (" << rect.x << ", " << rect.y << ", " << rect.width << ", " << rect.height << ")\n";
+    return 0;
+}
+```
+
+## 相关文档
+
+- [`Viewport::GetAspectRatio`](getaspectratio.md) - 获取宽高比
+- [Viewport 总览](viewport.md)

docs/api/math/viewport/viewport.md

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+# Viewport
+
+**命名空间**: `XCEngine::Math`
+
+**类型**: `struct`
+
+**头文件**: `XCEngine/Math/Viewport.h`
+
+**描述**: 视口，用于渲染目标区域和坐标映射
+
+## 概述
+
+Viewport 结构体表示一个渲染视口，除了位置和尺寸外，还包含深度范围 `(minDepth, maxDepth)`。主要用于屏幕到归一化设备坐标（NDC）的映射，以及渲染目标区域的定义。
+
+## 公共方法
+
+| 方法 | 描述 |
+|------|------|
+| [`GetAspectRatio`](getaspectratio.md) | 获取视口宽高比 |
+| [`GetRect`](getrect.md) | 转换为 Rect |
+
+## 使用示例
+
+```cpp
+#include "XCEngine/Math/Rect.h"
+#include <iostream>
+
+using namespace XCEngine::Math;
+
+int main() {
+    Viewport viewport(0.0f, 0.0f, 1920.0f, 1080.0f, 0.0f, 1.0f);
+    
+    std::cout << "Position: (" << viewport.x << ", " << viewport.y << ")\n";
+    std::cout << "Size: " << viewport.width << " x " << viewport.height << "\n";
+    std::cout << "Depth: " << viewport.minDepth << " to " << viewport.maxDepth << "\n";
+    std::cout << "Aspect Ratio: " << viewport.GetAspectRatio() << "\n";
+    
+    Rect rect = viewport.GetRect();
+    std::cout << "As Rect: (" << rect.x << ", " << rect.y << ", " << rect.width << ", " << rect.height << ")\n";
+    
+    return 0;
+}
+```
+
+## 相关文档
+
+- [`Rect`](../rect/rect.md) - 浮点矩形
+- [`RectInt`](../rect/rectint.md) - 整数矩形
+- [`Vector2`](../vector2/vector2.md) - 二维向量