refactor(platform): Encapsulate state in PlatformState struct

- Replaced all global static variables in the platform layer with a single PlatformState struct.
- Updated all platform function signatures to accept a pointer to this struct, making the implementation stateless and more modular.
- Refactored main.cc, tests, and tools to instantiate and pass the PlatformState struct.
- This improves code organization and removes scattered global state.

1 files changed, 37 insertions, 16 deletions

diff --git a/src/platform.h b/src/platform.h
index 38a0568..2d2fc9e 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -1,25 +1,46 @@
-// This file is part of the 64k demo project.
-// It defines the platform abstraction layer for windowing and input.
-// Provides a consistent interface for GLFW-based operations.
+// Handles windowing, input, and native surface creation.
 
 #pragma once
 
-#include <webgpu.h>
-
 // Forward declare GLFWwindow to avoid including the full header here.
 struct GLFWwindow;
 
-void platform_init_window(bool fullscreen, int* width_ptr, int* height_ptr);
-void platform_shutdown();
-void platform_poll();
-bool platform_should_close();
+struct PlatformState {
+  GLFWwindow* window = nullptr;
+  int width = 1280;
+  int height = 720;
+  bool is_fullscreen = false;
+  // Store windowed geometry for fullscreen toggle
+  int windowed_x = 0, windowed_y = 0, windowed_w = 0, windowed_h = 0;
+};
+
+void platform_init(PlatformState* state, bool fullscreen, int* width_ptr, int* height_ptr);
+void platform_shutdown(PlatformState* state);
+void platform_poll(PlatformState* state);
+bool platform_should_close(PlatformState* state);
+void platform_toggle_fullscreen(PlatformState* state);
+
+// Inline getters for direct access
+inline GLFWwindow* platform_get_window(PlatformState* state) { return state->window; }
+inline int platform_get_width(PlatformState* state) { return state->width; }
+inline int platform_get_height(PlatformState* state) { return state->height; }
+inline float platform_get_aspect_ratio(PlatformState* state) {
+  if (state->height == 0) return 1.0f;
+  return (float)state->width / (float)state->height;
+}
 
-GLFWwindow* platform_get_window();
-double platform_get_time();
+// glfwGetTime is a simple global query, so it doesn't need the state struct.
+// Include the header directly to get the proper linkage.
+#include <GLFW/glfw3.h>
+inline double platform_get_time() {
+    return glfwGetTime();
+}
 
-// Add dimension getters
-int platform_get_width();
-int platform_get_height();
-float platform_get_aspect_ratio();
 
-WGPUSurface platform_create_wgpu_surface(WGPUInstance instance);
+// WebGPU specific surface creation
+#if defined(DEMO_CROSS_COMPILE_WIN32)
+#include <webgpu/webgpu.h>
+#else
+#include <wgpu.h>
+#endif
+WGPUSurface platform_create_wgpu_surface(WGPUInstance instance, PlatformState* state);