How do i Use Fillrect or DrawText on 32bit HBITMAP in C++ - winapi

Question

i'm sorry for what i did. i edited.
i'd like to use Fillrect on 32bit HBITMAP which is Created with CreateDIBSection
but i can't make rect visible in color that i want to.
(i Drawed a fillrect with CreateSolidBrush blue(RGB(0, 0, 255)) on 32bit HBITMAP(hdcbmp), but it doesn't appear blue.)
here is source code
is there anyway to show rect color that i want to?
sorry for my poor english.
void DrawAlphaBitmap(HWND hWnd, ULONG uWidth, ULONG uHeight)
{
BLENDFUNCTION bf;
HBITMAP hbitmap;
HBITMAP hOldBitmap;
BITMAPINFO bmi;
PVOID pvBits;
HDC hdcwnd = GetDC(hWnd);
HDC hdcbmp = CreateCompatibleDC(hdcwnd);
ZeroMemory(&bmi, sizeof(BITMAPINFO));
bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth = uWidth;
bmi.bmiHeader.biHeight = uHeight;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
bmi.bmiHeader.biCompression = BI_RGB;
bmi.bmiHeader.biSizeImage = bmi.bmiHeader.biWidth * bmi.bmiHeader.biHeight * 4;
hbitmap = CreateDIBSection(hdcbmp, &bmi, DIB_RGB_COLORS, &pvBits, NULL, 0x0);
hOldBitmap = (HBITMAP)SelectObject(hdcbmp, hbitmap);
bf.BlendOp = AC_SRC_OVER;
bf.BlendFlags = 0;
bf.SourceConstantAlpha = 0xff;
bf.AlphaFormat = AC_SRC_ALPHA;
RECT rc2 = { 100, 100, 200, 200 };
FillRect(hdcbmp, &rc2, CreateSolidBrush(RGB(0, 0, 255)));
AlphaBlend(hdcwnd, 0, 0, uWidth, uHeight, hdcbmp, 0, 0, uWidth, uHeight, bf);
SelectObject(hdcbmp, hOldBitmap);
DeleteObject(hbitmap);
DeleteDC(hdcbmp);
ReleaseDC(hWnd, hdcwnd);
}

Answer 1

From documentation for BLENDFUNCTION:
AlphaFormat:
This flag is set when the bitmap has an Alpha channel (that is, per-pixel alpha).
In this case, alpha channel is not set. CreateDIBSection initializes the alpha values to zero. When AC_SRC_ALPHA is set, AlphaBlend ignores pixels whose alpha value is zero. Modify your code as follows:
//bf.AlphaFormat = AC_SRC_ALPHA; <- remove
bf.AlphaFormat = 0; //replace with 0
Side note, you have resource leak in creation of HBRUSH handle. Change the code to
HBRUSH hbrush = CreateSolidBrush(RGB(0, 0, 255));
RECT rc2 = { 0, 0, w, h };
FillRect(memdc, &rc2, hbrush);
DeleteObject(hbrush);
Ideally, your function prototype should be void DrawAlphaBitmap(HDC hdc, ULONG uWidth, ULONG uHeight); so that HDC can be passed directly, for example from BeginPaint/EndPaint in WM_PAINT message.