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-rw-r--r--win-resize-mt/build.sh3
-rw-r--r--win-resize-mt/win-resize-mt.c277
2 files changed, 280 insertions, 0 deletions
diff --git a/win-resize-mt/build.sh b/win-resize-mt/build.sh
new file mode 100644
index 0000000..c7c4423
--- /dev/null
+++ b/win-resize-mt/build.sh
@@ -0,0 +1,3 @@
+#!/bin/bash
+mkdir -p bin
+cc -o bin/win-resize-mt -Wall -Wextra -Wpedantic -O0 -g ./win-resize-mt.c -ldwmapi -lgdi32
diff --git a/win-resize-mt/win-resize-mt.c b/win-resize-mt/win-resize-mt.c
new file mode 100644
index 0000000..2f9dd4e
--- /dev/null
+++ b/win-resize-mt/win-resize-mt.c
@@ -0,0 +1,277 @@
+// ================================================================================================
+// Example of how to draw while resizing / moving a window on Windows in C.
+//
+// This demo uses a dedicated render thread with basic synchronization with the event loop. There
+// is a single-threaded version called win-resize/ if that's more your style.
+//
+// Build (MSVC):
+// > cl /W4 /Od /Zi win-resize-mt.c /Fe:win-resize-mt.exe
+// Build (GCC/clang):
+// $ cc -o win-resize-mt.exe -Wall -Wextra -Wpedantic -O0 -g win-resize-mt.c -ldwmapi -lgdi32
+//
+// Changelog:
+// XX/XX/XXXX: Initial release
+//
+// License:
+// Copyright (c) 2026 Hunter Kvalevog
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE.
+// ================================================================================================
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#include <dwmapi.h>
+
+#include <assert.h>
+#include <math.h>
+#include <stdio.h>
+
+#ifdef _MSC_VER
+# pragma comment(lib, "dwmapi.lib")
+# pragma comment(lib, "gdi32.lib")
+# pragma comment(lib, "user32.lib")
+#endif
+
+#define UNUSED(Var) ((void)(Var))
+
+static void GfxInit(HWND wnd);
+static void GfxResize(UINT vpw, UINT vph);
+static void GfxDraw(void);
+
+#define THREAD_BIT_QUIT (1 << 0)
+#define THREAD_BIT_SIZE (1 << 1)
+#define THREAD_BIT_SYNC (1 << 2)
+
+typedef struct ThreadData ThreadData;
+struct ThreadData
+{
+ HWND wnd;
+ HANDLE init_sig;
+ HANDLE sync_sig;
+ volatile LONG bits;
+ volatile LONG size_w;
+ volatile LONG size_h;
+};
+
+//
+static DWORD WINAPI RenderThread(LPVOID opaque)
+{
+ ThreadData *td = opaque;
+ GfxInit(td->wnd);
+ GfxDraw();
+
+ SetEvent(td->init_sig);
+
+ while (TRUE) {
+ const LONG bits = InterlockedOr(&td->bits, 0);
+
+ if (bits & THREAD_BIT_QUIT) {
+ break;
+ }
+
+ if (bits & THREAD_BIT_SIZE) {
+ const LONG size_w = InterlockedOr(&td->size_w, 0);
+ const LONG size_h = InterlockedOr(&td->size_h, 0);
+ GfxResize(size_w, size_h);
+ InterlockedAnd(&td->bits, ~THREAD_BIT_SIZE);
+ }
+
+ GfxDraw();
+
+ if (bits & THREAD_BIT_SYNC) {
+ SetEvent(td->sync_sig);
+ InterlockedAnd(&td->bits, ~THREAD_BIT_SYNC);
+ }
+ }
+
+ return 0;
+}
+
+//
+static LRESULT CALLBACK WndProc(HWND wnd, UINT msg, WPARAM wparam, LPARAM lparam)
+{
+ ThreadData *td = (ThreadData *)GetWindowLongPtrW(wnd, GWLP_USERDATA);
+ switch (msg)
+ {
+ case WM_DESTROY:
+ PostQuitMessage(0);
+ return 0;
+ case WM_SIZE:
+ // Resize
+ InterlockedExchange(&td->size_w, LOWORD(lparam));
+ InterlockedExchange(&td->size_h, HIWORD(lparam));
+ InterlockedOr(&td->bits, THREAD_BIT_SIZE);
+
+ // Sync
+ InterlockedOr(&td->bits, THREAD_BIT_SYNC);
+ WaitForSingleObject(td->sync_sig, INFINITE);
+ ResetEvent(td->sync_sig);
+ break;
+ }
+ return DefWindowProcW(wnd, msg, wparam, lparam);
+}
+
+//
+int WinMain(HINSTANCE instance, HINSTANCE previnstance, LPSTR cmdline, int cmdshow)
+{
+ UNUSED(previnstance); UNUSED(cmdline);
+
+ // Register window class
+ WNDCLASSEXW wc = { 0 };
+ wc.cbSize = sizeof(wc);
+ wc.hCursor = LoadCursor(0, IDC_ARROW);
+ wc.hInstance = instance;
+ wc.lpfnWndProc = WndProc;
+ wc.lpszClassName = L"win-resize-mt";
+
+ ATOM atom = RegisterClassExW(&wc);
+ assert(atom && "Failed to register window class");
+
+ // Create window
+ HWND wnd = CreateWindowExW(WS_EX_APPWINDOW, wc.lpszClassName, wc.lpszClassName,
+ WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
+ CW_USEDEFAULT, 0, 0, wc.hInstance, 0);
+ assert(wnd && "Failed to create window");
+
+ //
+ ThreadData td = { 0 };
+ td.wnd = wnd;
+ td.init_sig = CreateEvent(0, TRUE, FALSE, 0);
+ td.sync_sig = CreateEvent(0, TRUE, FALSE, 0);
+
+ //
+ HANDLE th = CreateThread(0, 0, RenderThread, &td, 0, 0);
+ assert(th && "Failed to create render thread");
+
+ //
+ SetWindowLongPtrW(wnd, GWLP_USERDATA, (LONG_PTR)&td);
+ WaitForSingleObject(td.init_sig, INFINITE);
+
+ //
+ ShowWindow(wnd, cmdshow);
+
+ //
+ MSG msg;
+ while (GetMessageW(&msg, 0, 0, 0) > 0) {
+ TranslateMessage(&msg);
+ DispatchMessage(&msg);
+ }
+
+ //
+ InterlockedOr(&td.bits, THREAD_BIT_QUIT);
+ WaitForSingleObject(th, INFINITE);
+
+ return 0;
+}
+
+// ================================================================================================
+
+static UINT g_vpw = 0;
+static UINT g_vph = 0;
+static HDC g_hdc = 0;
+static HDC g_hdc_back = 0;
+static HBITMAP g_bmp = 0;
+static HBRUSH g_bgbr = 0;
+static HBRUSH g_fgbr = 0;
+static HPEN g_pen = 0;
+
+static void GfxInit(HWND wnd)
+{
+ g_hdc = GetDC(wnd);
+ g_hdc_back = CreateCompatibleDC(g_hdc);
+ g_bgbr = CreateSolidBrush(RGB(0x00, 0x20, 0x20));
+ g_fgbr = CreateSolidBrush(RGB(0xE0, 0xE0, 0xE0));
+ g_pen = CreatePen(PS_SOLID, 2, RGB(0xFF, 0x10, 0x10));
+
+ RECT rc;
+ GetClientRect(wnd, &rc);
+
+ GfxResize(rc.right, rc.bottom);
+}
+
+static void GfxResize(UINT vpw, UINT vph)
+{
+ if (g_bmp)
+ {
+ DeleteObject(g_bmp);
+ g_bmp = 0;
+ }
+
+ if (vpw > 0 && vph > 0)
+ {
+ g_bmp = CreateCompatibleBitmap(g_hdc, vpw, vph);
+ SelectObject(g_hdc_back, g_bmp);
+ }
+
+ g_vpw = vpw;
+ g_vph = vph;
+}
+
+static void GfxDraw(void)
+{
+ static UINT frame = 0;
+ ++frame;
+
+ if (g_bmp && g_vpw > 0 && g_vph > 0)
+ {
+ HDC hdc = g_hdc_back;
+
+ // Clear
+ {
+ RECT rc = { 0, 0, g_vpw, g_vph };
+ FillRect(hdc, &rc, g_bgbr);
+ }
+
+ // Draw X
+ {
+ SelectObject(hdc, g_pen);
+ MoveToEx(hdc, 0, 0, 0);
+ LineTo(hdc, g_vpw, g_vph);
+ MoveToEx(hdc, 0, g_vph, 0);
+ LineTo(hdc, g_vpw, 0);
+ }
+
+ // Draw rotating triangle
+ {
+ int cx = g_vpw / 2;
+ int cy = g_vph / 2;
+ int r = (g_vpw < g_vph ? g_vpw : g_vph) / 3;
+
+ POINT verts[3];
+ for (int i = 0; i < 3; ++i)
+ {
+ float ang = ((float)frame / 100.0f) + (float)i * (2.0f * 3.14159265f / 3.0f);
+ verts[i].x = cx + (int)(cosf(ang) * r);
+ verts[i].y = cy + (int)(sinf(ang) * r);
+ }
+
+ SelectObject(hdc, g_pen);
+ SelectObject(hdc, g_fgbr);
+ Polygon(hdc, verts, ARRAYSIZE(verts));
+ }
+
+ // Draw text
+ {
+ WCHAR txtbuf[256];
+ _snwprintf_s(txtbuf, ARRAYSIZE(txtbuf), _TRUNCATE, L"win-resize-mt (frame %u)", frame);
+
+ SIZE sz;
+ GetTextExtentPoint32W(hdc, txtbuf, (int)wcslen(txtbuf), &sz);
+
+ SetBkMode(hdc, TRANSPARENT);
+ SetTextColor(hdc, RGB(0xE0, 0xE0, 0xE0));
+ TextOutW(hdc, (g_vpw - sz.cx) / 2, 19, txtbuf, (int)wcslen(txtbuf));
+ }
+
+ // Present
+ BitBlt(g_hdc, 0, 0, g_vpw, g_vph, g_hdc_back, 0, 0, SRCCOPY);
+
+ // Wait for dwm to display a frame
+ DwmFlush();
+ }
+}
+
generated by cgit v1.2.3 (git 2.46.0) at 2026-06-19 10:39:26 +0000