feat: add window resize support

Added width/height tracking to the window class via a GLFW
resize callback. The callback stores the current size and
forwards it to a user-provided std::function.

Added context::set_size() to update the GL viewport when
the window is resized.

Changed scene::render() to accept (int width, int height)
parameters so scenes can compute the correct aspect ratio
for their projection matrix instead of hardcoding 1280/720.

Fixed parameter shadowing in resize_callback_impl
(glfw_window instead of window).

cbt/opengl/context.cpp

@@ -34,6 +34,9 @@ context::context(window const& win) {
         return;
     }
     m_valid = true;
+
+    // Set initial viewport to match window size
+    glViewport(0, 0, win.width(), win.height());
 }
 
 context::~context() {}
@@ -42,4 +45,8 @@ auto context::valid() const -> bool {
     return m_valid;
 }
 
+auto context::set_size(int width, int height) -> void {
+    glViewport(0, 0, width, height);
+}
+
 }

cbt/opengl/context.hpp

@@ -10,6 +10,7 @@ public:
     ~context();
 
     auto valid() const -> bool;
+    auto set_size(int width, int height) -> void;
 
 private:
     bool m_valid = false;

cbt/scene.cpp

@@ -8,6 +8,6 @@ auto scene::init() -> bool {
 
 auto scene::update(float) -> void {}
 
-auto scene::render() -> void {}
+auto scene::render(int, int) -> void {}
 
 }

cbt/scene.hpp

@@ -10,7 +10,7 @@ public:
 
     virtual auto init() -> bool;
     virtual auto update(float delta_time) -> void;
-    virtual auto render() -> void;
+    virtual auto render(int width, int height) -> void;
 };
 
 }

cbt/window.cpp

@@ -52,6 +52,12 @@ window::window(std::string title, int width, int height) {
         return;
     }
 
+    m_width = width;
+    m_height = height;
+
+    glfwSetWindowUserPointer(m_window, this);
+    glfwSetWindowSizeCallback(m_window, resize_callback_impl);
+
 #ifdef _WIN32
     auto hwnd = glfwGetWin32Window(m_window);
     BOOL use_dark_mode = TRUE;
@@ -94,6 +100,29 @@ auto window::stop() -> void {
     }
 }
 
+auto window::width() const -> int {
+    return m_width;
+}
+
+auto window::height() const -> int {
+    return m_height;
+}
+
+auto window::on_resize(resize_callback cb) -> void {
+    m_resize_cb = cb;
+}
+
+auto window::resize_callback_impl(GLFWwindow* glfw_window, int width, int height) -> void {
+    auto* self = static_cast<window*>(glfwGetWindowUserPointer(glfw_window));
+    if (self) {
+        self->m_width = width;
+        self->m_height = height;
+        if (self->m_resize_cb) {
+            self->m_resize_cb(width, height);
+        }
+    }
+}
+
 auto window::screenshot(std::string filepath) const -> bool {
     if (!m_window || !valid()) {
         return false;

cbt/window.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <functional>
 #include <string>
 
 #define GLFW_INCLUDE_NONE
@@ -19,13 +20,22 @@ public:
     auto raw() const -> GLFWwindow*;
     auto stop() -> void;
     auto screenshot(std::string filepath = "screenshot.png") const -> bool;
+    auto width() const -> int;
+    auto height() const -> int;
+
+    using resize_callback = std::function<void(int width, int height)>;
+    auto on_resize(resize_callback cb) -> void;
 
 private:
     GLFWwindow* m_window = nullptr;
+    int m_width = 0;
+    int m_height = 0;
+    resize_callback m_resize_cb;
     bool m_glfw_initialized = false;
 
     static auto init_glfw() -> bool;
     static auto terminate_glfw() -> void;
+    static auto resize_callback_impl(GLFWwindow* glfw_window, int width, int height) -> void;
 };
 
 }