allocating a backbuffer

code/Makefile

@@ -1,5 +1,5 @@
 comp:
-	zig c++ --target=x86_64-windows -o ../build/win32_handmade.exe win32_handmade.cpp -lgdi32
+	zig c++ --target=x86_64-windows -o ../build/win32_handmade.exe win32_handmade.cpp -lgdi32 -g
 .PHONY: clean
 clean: 
 	rm ../build/*

code/win32_handmade.cpp

@@ -2,17 +2,64 @@
 #include <windows.h>
 #include <wingdi.h>
 
-LRESULT CALLBACK MainWindowCallback(HWND window, UINT message, WPARAM wParam,
-                                    LPARAM lParam) {
+#define internal static
+#define local_persist static
+#define global_variable static
+
+// NOTE: this is a global for now
+global_variable bool running;
+global_variable BITMAPINFO bitmapInfo;
+global_variable void *bitmapMemory;
+global_variable HBITMAP bitmapHandle;
+global_variable HDC bitmapDeviceContext;
+
+internal void Win32ResizeDIBSection(int width, int height) {
+  // TODO: bulletproof this.
+  // perhaps don't free first, free after, then free first if that fails
+
+  if (bitmapHandle) {
+    DeleteObject(bitmapHandle);
+  }
+  if (!bitmapDeviceContext) {
+    // TODO: should we recreate these under certain special circumstances?
+    bitmapDeviceContext = CreateCompatibleDC(0);
+  }
+  bitmapInfo.bmiHeader.biSize = sizeof(bitmapInfo.bmiHeader);
+  bitmapInfo.bmiHeader.biWidth = width;
+  bitmapInfo.bmiHeader.biHeight = height;
+  bitmapInfo.bmiHeader.biPlanes = 1;
+  bitmapInfo.bmiHeader.biBitCount = 24;
+  bitmapInfo.bmiHeader.biCompression = BI_RGB;
+
+  bitmapHandle = CreateDIBSection(bitmapDeviceContext, &bitmapInfo,
+                                  DIB_RGB_COLORS, &bitmapMemory, 0, 0);
+}
+internal void Win32UpdateWindow(HDC deviceContext, int x, int y, int width,
+                                int height) {
+  StretchDIBits(deviceContext, x, y, width, height, x, y, width, height,
+                bitmapMemory, &bitmapInfo, DIB_RGB_COLORS, SRCCOPY);
+}
+
+LRESULT CALLBACK Win32MainWindowCallback(HWND window, UINT message,
+                                         WPARAM wParam, LPARAM lParam) {
   LRESULT res = 0;
   switch (message) {
   case WM_SIZE: {
+    RECT rect;
+    GetClientRect(window, &rect);
+    int width = rect.right - rect.left;
+    int height = rect.top - rect.bottom;
+    Win32ResizeDIBSection(width, height);
     printf("WM_SIZE\n");
   } break;
   case WM_DESTROY: {
+    running = false;
+    // TODO: handle this as an error - recreate window?
     printf("WM_DESTROY\n");
   } break;
   case WM_CLOSE: {
+    // TODO: handle this as a message to the user?
+    running = false;
     printf("WM_CLOSE\n");
   } break;
   case WM_PAINT: {
@@ -22,14 +69,8 @@ LRESULT CALLBACK MainWindowCallback(HWND window, UINT message, WPARAM wParam,
     int width = paint.rcPaint.right - paint.rcPaint.left;
     int x = paint.rcPaint.left;
     int y = paint.rcPaint.top;
+    Win32UpdateWindow(deviceContext, x, y, width, height);
 
-    static DWORD operation = WHITENESS;
-    PatBlt(deviceContext, x, y, width, height, operation);
-    if (operation == WHITENESS) {
-      operation = BLACKNESS;
-    } else {
-      operation = WHITENESS;
-    }
     EndPaint(window, &paint);
   } break;
   case WM_ACTIVATEAPP: {
@@ -44,11 +85,15 @@ LRESULT CALLBACK MainWindowCallback(HWND window, UINT message, WPARAM wParam,
   return res;
 }
 
+#undef RegisterClass
+#undef CreateWindowEx
+#undef GetMessage
+#undef DispatchMessage
+
 int CALLBACK WinMain(HINSTANCE instance, HINSTANCE prevInstance,
                      LPSTR commandLine, int showCode) {
   WNDCLASS WindowClass = {0};
-  WindowClass.style = CS_OWNDC | CS_HREDRAW | CS_VREDRAW;
-  WindowClass.lpfnWndProc = MainWindowCallback;
+  WindowClass.lpfnWndProc = Win32MainWindowCallback;
   // WindowClass.cbClsExtra = ;
   // WindowClass.cbWndExtra = ;
   WindowClass.hInstance = instance;
@@ -57,18 +102,19 @@ int CALLBACK WinMain(HINSTANCE instance, HINSTANCE prevInstance,
   // WindowClass.lpszMenuName = ;
   WindowClass.lpszClassName = "HandmadeHeroWindowClass";
 
-  if (RegisterClass(&WindowClass)) {
-    HWND windowHandle = CreateWindowEx(
+  if (RegisterClassA(&WindowClass)) {
+    HWND windowHandle = CreateWindowExA(
         0, WindowClass.lpszClassName, "Handmade Hero",
         WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT, CW_USEDEFAULT,
         CW_USEDEFAULT, CW_USEDEFAULT, 0, 0, instance, 0);
     if (windowHandle) {
+      running = true;
       MSG message;
-      for (;;) {
-        BOOL msgResult = GetMessage(&message, 0, 0, 0);
+      while (running) {
+        BOOL msgResult = GetMessageA(&message, 0, 0, 0);
         if (msgResult > 0) {
           TranslateMessage(&message);
-          DispatchMessage(&message);
+          DispatchMessageA(&message);
         } else {
           break;
         }