Win32 confusing flicker - c++

Question

I have a function in which a bunch of stuff is drawn into an offscreen buffer. At the end of the function, it calls InvalidateRect. For some reason, sometimes it redraws halfway through the function, causing a flicker. Here's the code for the function:
// Side Info
HBITMAP side = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_SIDEINFO));
hdcold = (HBITMAP)SelectObject(hbcmem, side);
BitBlt(hdcmem, 339, 26, 154, 300, hbcmem, 0, 0, SRCCOPY);
DrawLevelNumber(game.levelnumber);
if (color)
sprites = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_COLOR_SPRITES));
else sprites = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_BLACKWHITE_SPRITES));
hdcold = (HBITMAP)SelectObject(hbcmem, sprites);
// Find x and y coordinate for the top left of the visible screen
int x = game.Player_x, y = game.Player_y, ypos = 0;
if (x < 4) x = 4;
if (x > 27) x = 27;
if (y < 4) y = 4;
if (y > 27) y = 27;
x -= 4;
y -= 4;
// Draw lower layer
for (int i = 0; i < 9; i++)
{
for (int j = 0; j < 9; j++)
{
if (game.Layer_Two[x + i][y + j] != 0)
{
int xpos = game.get_pos(game.Layer_Two[x + i][y + j], ypos, false);
BitBlt(hdcmem, (i * 32) + 32, (j * 32) + 32, 32, 32, hbcmem, xpos, ypos, SRCCOPY);
}
}
}
// Draw upper layer
for (int i = 0; i < 9; i++)
{
for (int j = 0; j < 9; j++)
{
if ((game.Layer_Two[x + i][y + j] != 0 && game.Layer_One[x + i][y + j] >= 64 && game.Layer_One[x + i][y + j] <= 111))
{
int xpos = game.get_pos(game.Layer_One[x + i][y + j], ypos, true);
BitBlt(hdcmem, (i * 32) + 32, (j * 32) + 32, 32, 32, hbcmem, xpos + 96, ypos, SRCPAINT);
BitBlt(hdcmem, (i * 32) + 32, (j * 32) + 32, 32, 32, hbcmem, xpos, ypos, SRCAND);
} else {
int xpos = game.get_pos(game.Layer_One[x + i][y + j], ypos, false);
BitBlt(hdcmem, (i * 32) + 32, (j * 32) + 32, 32, 32, hbcmem, xpos, ypos, SRCCOPY);
}
}
}
// If it isn't started, show title
if (!game.started)
{
HDC tmphdc = CreateCompatibleDC(hdcmem);
HDC tmp = CreateCompatibleDC(tmphdc);
RECT rc;
GetClientRect(hWnd, &rc);
string str = game.leveltitle.substr(0, game.leveltitle.length() - 1) + "\nPassword: " + game.password;
TCHAR* tch = new TCHAR[str.length()];
mbstowcs_s(NULL, tch, _tcslen(tch), str.c_str(), str.length());
HFONT font = CreateFont(25, 0, 0, 0, FW_BOLD, false, false, false, ANSI_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY, FF_DONTCARE, NULL);
SelectObject(tmp, font);
DrawText(tmp, tch, str.length(), &rc, DT_CALCRECT);
rc.right += 16;
HBITMAP tmpbm = CreateCompatibleBitmap(hdcmem, rc.right, rc.bottom);
HBITMAP tmpold = (HBITMAP)SelectObject(tmphdc, tmpbm);
HBRUSH hbr = CreateSolidBrush(RGB(255, 255, 255));
HPEN pen = CreatePen(PS_SOLID, 1, RGB(255, 255, 255));
SelectObject(hdcmem, pen);
SelectObject(hdcmem, hbr);
Rectangle(hdcmem, 176 - (rc.right / 2), 243, 177 + (rc.right / 2), 248);
hbr = CreateSolidBrush(RGB(128, 128, 128));
pen = CreatePen(PS_SOLID, 1, RGB(128, 128, 128));
SelectObject(hdcmem, pen);
SelectObject(hdcmem, hbr);
Rectangle(hdcmem, 176 - (rc.right / 2), 294, 177 + (rc.right / 2), 299);
HBITMAP left = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_LEFT));
hdcold = (HBITMAP)SelectObject(hbcmem, left);
BitBlt(hdcmem, 176 - (rc.right / 2) - 4, 243, 4, 56, hbcmem, 0, 0, SRCCOPY);
HBITMAP right = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_RIGHT));
hdcold = (HBITMAP)SelectObject(hbcmem, right);
BitBlt(hdcmem, 176 + (rc.right / 2) + 1, 243, 4, 56, hbcmem, 0, 0, SRCCOPY);
SelectObject(tmphdc, font);
SetTextColor(tmphdc, RGB(255, 255, 0));
SetBkColor(tmphdc, RGB(0, 0, 0));
DrawText(tmphdc, tch, str.length(), &rc, DT_CENTER);
BITMAP structBitmapHeader;
memset( &structBitmapHeader, 0, sizeof(BITMAP) );
HGDIOBJ hBitmap = GetCurrentObject(tmphdc, OBJ_BITMAP);
GetObject(hBitmap, sizeof(BITMAP), &structBitmapHeader);
BitBlt(hdcmem, 176 - (rc.right / 2), 247, structBitmapHeader.bmWidth, structBitmapHeader.bmHeight, tmphdc, 0, 0, SRCCOPY);
}
// If paused
if (game.paused)
{
RECT rc;
rc.top = 32;
rc.left = 32;
rc.bottom = 330;
rc.right = 330;
BitBlt(hdcmem, 32, 32, 288, 288, NULL, 0, 0, BLACKNESS);
HFONT font = CreateFont(50, 0, 0, 0, FW_NORMAL, false, false, false, ANSI_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY, FF_DONTCARE, NULL);
SelectObject(hdcmem, font);
SetTextColor(hdcmem, RGB(255, 0, 0));
SetBkColor(hdcmem, RGB(0, 0, 0));
DrawText(hdcmem, L"PAUSED", 6, &rc, (DT_CENTER + DT_SINGLELINE + DT_VCENTER));
}
nums = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_NUMBERS));
hdcold = (HBITMAP)SelectObject(hbcmem, nums);
for (int i = 100; i > 0; i /= 10) // Coins left
{
int tmp;
if (i == 100)
tmp = game.coinsleft / 100;
if (i == 10)
tmp = ((game.coinsleft % 100) - (game.coinsleft % 10)) / 10;
if (i == 1)
tmp = game.coinsleft % 10;
if (game.coinsleft < i && i > 1)
tmp = 10;
int ypos = game.get_num_pos(tmp, (game.coinsleft == 0));
BitBlt(hdcmem, 369 + ((3 - log10((double)i)) * 17), 215, 17, 23, hbcmem, 0, ypos, SRCCOPY);
if (i == 100)
tmp = game.timeleft / 100;
if (i == 10)
tmp = ((game.timeleft % 100) - (game.timeleft % 10)) / 10;
if (i == 1)
tmp = game.timeleft % 10;
if (game.timeleft < i && i > 1)
tmp = 10;
if (game.timelimit == 0)
tmp = 11;
ypos = game.get_num_pos(tmp, (game.timeleft < 16 || game.timelimit == 0));
BitBlt(hdcmem, 369 + ((3 - log10((double)i)) * 17), 125, 17, 23, hbcmem, 0, ypos, SRCCOPY);
}
if (game.onhint)
{
HBITMAP sidebg = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_SIDEBG));
hdcold = (HBITMAP)SelectObject(hbcmem, sidebg);
BitBlt(hdcmem, 353, 165, 127, 146, hbcmem, 0, 0, SRCCOPY);
} else {
hdcold = (HBITMAP)SelectObject(hbcmem, sprites); // LOWER SIDE INFO
if (game.key1 > 0)
BitBlt(hdcmem, 352, 247, 32, 32, hbcmem, 192, 160, SRCCOPY);
else BitBlt(hdcmem, 352, 247, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.key2 > 0)
BitBlt(hdcmem, 384, 247, 32, 32, hbcmem, 192, 128, SRCCOPY);
else BitBlt(hdcmem, 384, 247, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.key3 > 0)
BitBlt(hdcmem, 416, 247, 32, 32, hbcmem, 192, 224, SRCCOPY);
else BitBlt(hdcmem, 416, 247, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.key4)
BitBlt(hdcmem, 448, 247, 32, 32, hbcmem, 192, 192, SRCCOPY);
else BitBlt(hdcmem, 448, 247, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.water)
BitBlt(hdcmem, 352, 279, 32, 32, hbcmem, 192, 256, SRCCOPY);
else BitBlt(hdcmem, 352, 279, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.fire)
BitBlt(hdcmem, 384, 279, 32, 32, hbcmem, 192, 288, SRCCOPY);
else BitBlt(hdcmem, 384, 279, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.ice)
BitBlt(hdcmem, 416, 279, 32, 32, hbcmem, 192, 320, SRCCOPY);
else BitBlt(hdcmem, 416, 279, 32, 32, hbcmem, 0, 0, SRCCOPY);
if (game.suction)
BitBlt(hdcmem, 448, 279, 32, 32, hbcmem, 192, 352, SRCCOPY);
else BitBlt(hdcmem, 448, 279, 32, 32, hbcmem, 0, 0, SRCCOPY);
}
RECT rc;
rc.left = 0;
rc.top = 0;
rc.right = 518;
rc.bottom = 401;
InvalidateRect(hWnd, &rc, false);
What is causing the flicker?

Answer 1

Ensure that you handle the WM_ERASEBKGND message and return TRUE, this will prevent the window base class from drawing the background.
Instead of calling InvalidateRect at the end of your drawing routine, place your drawing code inside a WM_PAINT message handler, this ensures your drawing code is called whenever the window is being repainted.