vg - Page 2 - Developer IT

Windows splash screen using GDI+

- by Luther

The eventual aim of this is to have a splash screen in windows that uses transparency but that's not what I'm stuck on at the moment. In order to create a transparent window, I'm first trying to composite the splash screen and text on an off screen buffer using GDI+. At the moment I'm just trying to composite the buffer and display it in response to a 'WM_PAINT' message. This isn't working out at the moment; all I see is a black window. I imagine I've misunderstood something with regards to setting up render targets in GDI+ and then rendering them (I'm trying to render the screen using straight forward GDI blit) Anyway, here's the code so far: //my window initialisation code void MyWindow::create_hwnd(HINSTANCE instance, const SIZE &dim) { DWORD ex_style = WS_EX_LAYERED ; //eventually I'll be making use of this layerd flag m_hwnd = CreateWindowEx( ex_style, szFloatingWindowClass , L"", WS_POPUP , 0, 0, dim.cx, dim.cy, null, null, instance, null); SetWindowLongPtr(m_hwnd ,0, (__int3264)(LONG_PTR)this); m_display_dc = GetDC(NULL); //This was sanity check test code - just loading a standard HBITMAP and displaying it in WM_PAINT. It worked fine //HANDLE handle= LoadImage(NULL , L"c:\\test_image2.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE); m_gdip_offscreen_bm = new Gdiplus::Bitmap(dim.cx, dim.cy); m_gdi_dc = Gdiplus::Graphics::FromImage(m_gdip_offscreen_bm);//new Gdiplus::Graphics(m_splash_dc );//window_dc ;m_splash_dc //this draws the conents of my splash screen - this works if I create a GDI+ context for the window, rather than for an offscreen bitmap. //For all I know, it might actually be working but when I try to display the contents on screen, it shows a black image draw_all(); //this is just to show that drawing something simple on the offscreen bit map seems to have no effect Gdiplus::Pen pen(Gdiplus::Color(255, 0, 0, 255)); m_gdi_dc->DrawLine(&pen, 0,0,100,100); DWORD last_error = GetLastError(); //returns '0' at this stage } And here's the snipit that handles the WM_PAINT message: ---8<----------------------- //Paint message snippit case WM_PAINT: { BITMAP bm; PAINTSTRUCT ps; HDC hdc = BeginPaint(vg->m_hwnd, &ps); //get the HWNDs DC HDC hdcMem = vg->m_gdi_dc->GetHDC(); //get the HDC from our offscreen GDI+ object unsigned int width = vg->m_gdip_offscreen_bm->GetWidth(); //width and height seem fine at this point unsigned int height = vg->m_gdip_offscreen_bm->GetHeight(); BitBlt(hdc, 0, 0, width, height, hdcMem, 0, 0, SRCCOPY); //this blits a black rectangle DWORD last_error = GetLastError(); //this was '0' vg->m_gdi_dc->ReleaseHDC(hdcMem); EndPaint(vg->m_hwnd, &ps); //end paint return 1; } ---8<----------------------- My apologies for the long post. Does anybody know what I'm not quite understanding regarding how you write to an offscreen buffer using GDI+ (or GDI for that matter)and then display this on screen? Thank you for reading.

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