Add double-buffering - No more flicker!

WatchfulEye/src/Application.cpp

@@ -39,6 +39,8 @@ namespace watchfuleye {
         , m_greenBrush(nullptr)
         , m_yellowBrush(nullptr)
         , m_redBrush(nullptr)
+        , m_offscreenDC(nullptr)
+        , m_offscreenBitmap(nullptr)
     {
         std::cout << std::format("{} {}\n", m_appName, m_appVersion);
     }
@@ -114,9 +116,9 @@ namespace watchfuleye {
                 app->m_yellowBrush =    CreateSolidBrush(RGB(255, 255, 150));
                 app->m_redBrush =       CreateSolidBrush(RGB(255, 150, 150));
 
-                // App will update (repaint) every second
+                // App will update (repaint) at 5 FPS
                 SendMessage(hWnd, WM_UPDATE, NULL, NULL);
-                SetTimer(hWnd, IDT_UPDATE, 1000, nullptr);
+                SetTimer(hWnd, IDT_UPDATE, 200, nullptr);
 
                 return 0;
             }
@@ -167,7 +169,7 @@ namespace watchfuleye {
                 if (HIWORD(wParam) == 0 && LOWORD(wParam) == IDM_ABOUT) {
                     MessageBox(hWnd, std::format("{} {}\nCopyright Grayson Riffe 2026\ngraysonriffe.com\n\n"
                         "\t{} is a simple countdown application\n"
-                        "specifically designed for this electronics testing labratory.\n\n"
+                        "specifically designed for this electronics testing labratory.\n"
                         "Hopefully, it's working!", app->m_appName, app->m_appVersion,
                         app->m_appName).c_str(), std::format("About {}", app->m_appName).c_str(), MB_OK);
 
@@ -198,12 +200,32 @@ namespace watchfuleye {
                 return 0;
             }
 
-            case WM_ERASEBKGND: {
+            case WM_ERASEBKGND: { // Don't erase the background, it is already done in WM_PAINT
-                HDC hDC = reinterpret_cast<HDC>(wParam);
+                return 1;
+            }
+
+            case WM_PAINT: {
+                PAINTSTRUCT ps = {};
+                HDC hDC = BeginPaint(hWnd, &ps);
 
                 RECT clientRect = {};
                 GetClientRect(hWnd, &clientRect);
 
+                // Create offscreen buffer if not already created
+                if (!app->m_offscreenDC) {
+                    app->m_offscreenDC = CreateCompatibleDC(hDC);
+                    app->m_offscreenBitmap = CreateCompatibleBitmap(hDC, clientRect.right - clientRect.left, clientRect.bottom - clientRect.top);
+                }
+
+                // Setup RECTs
+                RECT timeRect = clientRect;
+                timeRect.top -= 25, timeRect.bottom -= 25;
+
+                RECT lowerRect = { .top = WINDOW_HEIGHT - 65, .right = WINDOW_WIDTH, .bottom = WINDOW_HEIGHT };
+
+                HANDLE prevBitmap = SelectObject(app->m_offscreenDC, app->m_offscreenBitmap);
+
+                // Fill background
                 HBRUSH backgroundBrush = nullptr;
 
                 if (!app->m_active)
@@ -215,25 +237,11 @@ namespace watchfuleye {
                 else
                     backgroundBrush = app->m_yellowBrush;
 
-                FillRect(hDC, &clientRect, backgroundBrush);
+                FillRect(app->m_offscreenDC, &clientRect, backgroundBrush);
-
-                return 1;
-            }
-
-            case WM_PAINT: {
-                PAINTSTRUCT ps = {};
-                HDC hDC = BeginPaint(hWnd, &ps);
-
-                // Setup RECTs
-                RECT timeRect = {};
-                GetClientRect(hWnd, &timeRect);
-                timeRect.top -= 25, timeRect.bottom -= 25;
-
-                RECT lowerRect = { .top = WINDOW_HEIGHT - 65, .right = WINDOW_WIDTH, .bottom = WINDOW_HEIGHT };
 
                 // Setup text options
-                SetTextColor(hDC, RGB(0, 0, 0));
+                SetTextColor(app->m_offscreenDC, RGB(0, 0, 0));
-                SetBkMode(hDC, TRANSPARENT);
+                SetBkMode(app->m_offscreenDC, TRANSPARENT);
 
                 // Calculate time
                 Seconds elapsed = Duration(Clock::now() - app->m_startTime).count();
@@ -242,29 +250,33 @@ namespace watchfuleye {
                     remaining -= elapsed;
 
                 if (!app->m_active || (app->m_active && !app->m_overTime)) { // Draw time
-                    SelectObject(hDC, app->m_timeFont);
+                    SelectObject(app->m_offscreenDC, app->m_timeFont);
                     unsigned int minutes = remaining % (3600) / 60, seconds = remaining % 60;
-                    DrawText(hDC, std::format("{:02}:{:02}", minutes, seconds).c_str(), -1, &timeRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
+                    DrawText(app->m_offscreenDC, std::format("{:02}:{:02}", minutes, seconds).c_str(), -1, &timeRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
                 }
 
                 if (!app->m_active) { // Ready (green)
-                    SelectObject(hDC, app->m_lowerFont);
+                    SelectObject(app->m_offscreenDC, app->m_lowerFont);
-                    DrawText(hDC, "Ready", -1, &lowerRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
+                    DrawText(app->m_offscreenDC, "Ready", -1, &lowerRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
                 }
                 else if (!app->m_overTime) { // Counting (yellow)
-                    SelectObject(hDC, app->m_lowerFont);
+                    SelectObject(app->m_offscreenDC, app->m_lowerFont);
-                    DrawText(hDC, "Time Remaining on Tester", -1, &lowerRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
+                    DrawText(app->m_offscreenDC, "Time Remaining on Tester", -1, &lowerRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
                 }
                 else { // Over time (red)
-                    SelectObject(hDC, app->m_lowerFont);
+                    SelectObject(app->m_offscreenDC, app->m_lowerFont);
-                    DrawText(hDC, "Please Eject Your USB", -1, &lowerRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
+                    DrawText(app->m_offscreenDC, "Please Eject Your USB", -1, &lowerRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
-                    SelectObject(hDC, app->m_timeFont);
+                    SelectObject(app->m_offscreenDC, app->m_timeFont);
-                    DrawText(hDC, "STOP", -1, &timeRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
+                    DrawText(app->m_offscreenDC, "STOP", -1, &timeRect, DT_SINGLELINE | DT_NOCLIP | DT_CENTER | DT_VCENTER);
                 }
 
                 if (remaining <= 0)
                     app->m_overTime = true;
 
+                BitBlt(hDC, 0, 0, clientRect.right - clientRect.left, clientRect.bottom - clientRect.top, app->m_offscreenDC, 0, 0, SRCCOPY);
+
+                SelectObject(app->m_offscreenDC, prevBitmap);
+
                 EndPaint(hWnd, &ps);
                 return 0;
             }
@@ -335,5 +347,8 @@ namespace watchfuleye {
         DeleteObject(m_greenBrush);
         DeleteObject(m_yellowBrush);
         DeleteObject(m_redBrush);
+
+        DeleteObject(m_offscreenBitmap);
+        DeleteDC(m_offscreenDC);
     }
 }

WatchfulEye/src/Application.h

@@ -38,5 +38,7 @@ namespace watchfuleye {
         HRGN m_region;
         HFONT m_timeFont, m_lowerFont;
         HBRUSH m_greenBrush, m_yellowBrush, m_redBrush;
+        HDC m_offscreenDC;
+        HBITMAP m_offscreenBitmap;
     };
 }