Direct2D DC context rendered images doesn't appear on startup - c++

Question

I have simple application with a native winapi window, and a static control on it as a child window. I'd like to draw on the child window with Direct2D.
The drawing happens outside of the WM_PAINT message, so I decided to use ID2D1DCRenderTarget. Everything works except one thing. I can't make the drawing visible when the application starts.
If I do painting in any event (for example in WM_LBUTTONDOWN) the drawing shows up. But if I do painting in WM_CREATE I see nothing on the screen.
Here is my example code:
#include <iostream>
#include <windows.h>
#include <windowsx.h>
#include <d2d1.h>
#pragma comment(lib, "d2d1.lib")
HWND windowHandle = NULL;
HWND childWindowHandle = NULL;
ID2D1Factory* direct2DFactory = nullptr;
ID2D1DCRenderTarget* renderTarget = nullptr;
static void InitDirect2D ()
{
D2D1CreateFactory (D2D1_FACTORY_TYPE_SINGLE_THREADED, &direct2DFactory);
D2D1_RENDER_TARGET_PROPERTIES props = D2D1::RenderTargetProperties(
D2D1_RENDER_TARGET_TYPE_DEFAULT,
D2D1::PixelFormat(
DXGI_FORMAT_B8G8R8A8_UNORM,
D2D1_ALPHA_MODE_IGNORE),
0,
0,
D2D1_RENDER_TARGET_USAGE_NONE,
D2D1_FEATURE_LEVEL_DEFAULT
);
direct2DFactory->CreateDCRenderTarget (&props, &renderTarget);
renderTarget->SetAntialiasMode (D2D1_ANTIALIAS_MODE_ALIASED);
}
static void Paint ()
{
ID2D1SolidColorBrush* blackBrush = nullptr;
renderTarget->CreateSolidColorBrush (
D2D1::ColorF (D2D1::ColorF::Black),
&blackBrush
);
renderTarget->BeginDraw ();
renderTarget->SetTransform (D2D1::Matrix3x2F::Identity ());
renderTarget->Clear (D2D1::ColorF (D2D1::ColorF::LightGray));
D2D1_RECT_F rect = D2D1::RectF (10.0f, 10.0f, 100.0f, 100.0f);
renderTarget->DrawRectangle (&rect, blackBrush);
renderTarget->EndDraw ();
}
static LRESULT CALLBACK ChildWindowProc (HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch (msg) {
case WM_CREATE:
{
RECT rc;
GetClientRect (hwnd, &rc);
renderTarget->BindDC (GetDC (hwnd), &rc);
Paint ();
}
break;
case WM_LBUTTONDOWN:
Paint ();
break;
case WM_PAINT:
break;
case WM_SIZE:
{
RECT rc;
GetClientRect (hwnd, &rc);
renderTarget->BindDC (GetDC (hwnd), &rc);
Paint ();
}
break;
case WM_CLOSE:
DestroyWindow (hwnd);
break;
case WM_DESTROY:
PostQuitMessage (0);
break;
break;
}
LRESULT res = DefWindowProc (hwnd, msg, wParam, lParam);
return res;
}
static void CreateChildWindow (HWND parentHandle)
{
WNDCLASSEX windowClass;
memset (&windowClass, 0, sizeof (WNDCLASSEX));
windowClass.cbSize = sizeof(WNDCLASSEX);
windowClass.style = 0;
windowClass.lpfnWndProc = ChildWindowProc;
windowClass.style = CS_DBLCLKS;
windowClass.cbClsExtra = 0;
windowClass.cbWndExtra = 0;
windowClass.hInstance = NULL;
windowClass.hCursor = LoadCursor (NULL, IDC_ARROW);
windowClass.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1);
windowClass.lpszMenuName = NULL;
windowClass.lpszClassName = L"ChildWindowClass";
RegisterClassEx (&windowClass);
childWindowHandle = CreateWindowEx (
0, windowClass.lpszClassName, L"", WS_CHILD,
CW_USEDEFAULT, CW_USEDEFAULT, 0, 0, parentHandle, NULL, NULL, nullptr
);
ShowWindow (childWindowHandle, SW_SHOW);
UpdateWindow (childWindowHandle);
MoveWindow (childWindowHandle, 10, 10, 780, 580, TRUE);
}
static LRESULT CALLBACK MainWindowProc (HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
if (msg == WM_CREATE) {
CreateChildWindow (hwnd);
InvalidateRect (hwnd, NULL, FALSE);
}
switch (msg) {
case WM_SIZE:
{
int newWidth = LOWORD (lParam);
int newHeight = HIWORD (lParam);
MoveWindow (childWindowHandle, 10, 10, newWidth - 20, newHeight - 20, TRUE);
}
break;
case WM_CLOSE:
DestroyWindow (hwnd);
break;
case WM_DESTROY:
PostQuitMessage (0);
break;
}
return DefWindowProc (hwnd, msg, wParam, lParam);
}
static int CreateMainWindow ()
{
WNDCLASSEX windowClass;
memset (&windowClass, 0, sizeof (WNDCLASSEX));
windowClass.cbSize = sizeof (WNDCLASSEX);
windowClass.style = 0;
windowClass.lpfnWndProc = MainWindowProc;
windowClass.style = CS_DBLCLKS;
windowClass.cbClsExtra = 0;
windowClass.cbWndExtra = 0;
windowClass.hInstance = NULL;
windowClass.hIcon = LoadIcon (NULL, IDI_APPLICATION);
windowClass.hCursor = LoadCursor (NULL, IDC_ARROW);
windowClass.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1);
windowClass.lpszMenuName = NULL;
windowClass.lpszClassName = L"WindowClass";
windowClass.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
RegisterClassEx (&windowClass);
RECT requiredRect = { 0, 0, 800, 600 };
HWND windowHandle = CreateWindowEx (
WS_EX_WINDOWEDGE, windowClass.lpszClassName, L"Example", WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT, requiredRect.right - requiredRect.left, requiredRect.bottom - requiredRect.top, NULL, NULL, NULL, nullptr
);
if (windowHandle == NULL) {
return 1;
}
ShowWindow (windowHandle, SW_SHOW);
UpdateWindow (windowHandle);
MSG msg;
while (GetMessage (&msg, NULL, 0, 0)) {
TranslateMessage (&msg);
DispatchMessage (&msg);
}
return 0;
}
int main (int argc, char* argv[])
{
InitDirect2D ();
return CreateMainWindow ();
}
Do you have any idea how can I make the drawing visible on application startup?

Answer 1

During WM_CREATE window is not complitely created yet so painting does not work. You should write a proper WM_PAINT (and WM_ERASEBKGND) message handlers and perform all the painting operations there. Then when you need to redraw as a response to any other message (such as WM_LBUTTONDOWN) you need to invalidate window and trigger WM_PAINT instead of immediately calling Paint();.