[英]Why is drawing to a hidden HDC giving different results than when drawing to the HDC returned by GetDC(HWND)
我有兩種方法,paintDoubleBuffered 和 paint。 他們都應該在屏幕上繪制這個圖像:
該圖像由大約 12 個較小的圖像組成,每個圖像的大小為 256x256,平鋪在一起。
我的標准繪畫方法按預期工作。 這里是:
void MainWindow::paint(HWND hwnd) {
HDC hdc{GetDC(hwnd)};
paint(hwnd, hdc);
ReleaseDC(hwnd, hdc);
}
void MainWindow::paint(HWND hwnd, HDC hdc) {
constexpr INT img_width{ MDNR_Map::pannel_width };
constexpr INT img_height{ MDNR_Map::pannel_height };
const INT width{ GetDeviceCaps(hdc, HORZRES) };
const INT height{ GetDeviceCaps(hdc, VERTRES) };
const INT num_width_pannels{ (width / img_width) + 1 };
const INT num_height_pannels{ (height / img_height) + 1 };
Gdiplus::Graphics g(hdc);
g.SetCompositingMode(CompositingMode::CompositingModeSourceCopy);
g.SetInterpolationMode(InterpolationMode::InterpolationModeNearestNeighbor);
for (INT y = 0; y < num_height_pannels; y++) {
for (INT x = 0; x < num_width_pannels; x++) {
Location_t get_loaction(x + map_location.x, y + map_location.y, map_location.layer);
const IMG_t v{ mdnr_map.get(get_loaction) };
const Point drawPoint((INT)(img_width * x), (INT)(img_height * y));
Status stat{ g.DrawImage(v, drawPoint) };
if (stat != Status::Ok)
{
throw std::runtime_error(":(");
}
}
}
}
該繪制方法的問題是 mdnr_map.get 是一個 io 綁定調用,可能需要幾微秒。 因為我需要調用它大約 12 次,所以它會導致閃爍。
為了解決這個問題,我嘗試寫了一個雙緩沖的paint方法,如下:
void MainWindow::paintDoubleBuffered(HWND hwnd) {
// Get DC for window
HDC hdc{ GetDC(hwnd) };
const INT win_width{ GetDeviceCaps(hdc, HORZRES) };
const INT win_height{ GetDeviceCaps(hdc, VERTRES) };
// Create an off-screen DC for double-buffering
HDC hdcMem{ CreateCompatibleDC(hdc) };
HBITMAP hbmMem{ CreateCompatibleBitmap(hdc, win_width, win_height) };
HANDLE hOld{ SelectObject(hdcMem, hbmMem) };
// Draw into hdcMem here
paint(hwnd, hdcMem);
// Transfer the off-screen DC to the screen
BitBlt(hdc, 0, 0, win_width, win_height, hdcMem, 0, 0, SRCCOPY);
// Free-up the off-screen DC
SelectObject(hdcMem, hOld);
DeleteObject(hbmMem);
DeleteDC(hdcMem);
}
稍微戳了一下,我發現如果我通過將圖像大小乘以 1.5 來改變我的雙緩沖繪畫方法,圖像不再那么亂碼,但現在放大了 1.5 倍
void MainWindow::paintDoubleBuffered(HWND hwnd) {
// Get DC for window
HDC hdc{ GetDC(hwnd) };
const INT win_width{ GetDeviceCaps(hdc, HORZRES) };
const INT win_height{ GetDeviceCaps(hdc, VERTRES) };
// Create an off-screen DC for double-buffering
HDC hdcMem{ CreateCompatibleDC(hdc) };
HBITMAP hbmMem{ CreateCompatibleBitmap(hdc, win_width, win_height) };
HANDLE hOld{ SelectObject(hdcMem, hbmMem) };
// Draw into hdcMem here
constexpr INT img_width{ MDNR_Map::pannel_width + 128 }; // MDNR_Map::pannel_width is 256
constexpr INT img_height{ MDNR_Map::pannel_height + 128}; // MDNR_Map::pannel_height is 256
const INT num_width_pannels{ (win_width / img_width) + 1 };
const INT num_height_pannels{ (win_height / img_height) + 1 };
Gdiplus::Graphics g(hdcMem);
g.SetCompositingMode(CompositingMode::CompositingModeSourceCopy);
g.SetInterpolationMode(InterpolationMode::InterpolationModeNearestNeighbor);
for (INT y = 0; y < num_height_pannels; y++) {
for (INT x = 0; x < num_width_pannels; x++) {
Location_t get_loaction(x + map_location.x, y + map_location.y, map_location.layer);
Gdiplus::Bitmap* pannel{ mdnr_map.get(get_loaction) };
const Point drawPoint((INT)(img_width * x), (INT)(img_height * y));
Status stat{ g.DrawImage(pannel, drawPoint) };
if (stat != Status::Ok)
{
throw std::runtime_error(":(");
}
}
}
// Transfer the off-screen DC to the screen
BitBlt(hdc, 0, 0, win_width, win_height, hdcMem, 0, 0, SRCCOPY);
// Free-up the off-screen DC
SelectObject(hdcMem, hOld);
DeleteObject(hbmMem);
DeleteDC(hdcMem);
}
我的問題是,為什么繪制到 CreateCompatibleBitmap 返回的 HDC 會產生與繪制到 GetDC 返回的 HDC 不同的結果?
我已經嘗試過: BltBlt 的所有光柵操作代碼。 我檢查過臨時 HDC 的大小與 window 相同。我嘗試替換代碼片段
const INT win_width{ GetDeviceCaps(hdc, HORZRES) };
const INT win_height{ GetDeviceCaps(hdc, VERTRES) };
和
RECT rect;
GetWindowRect(hwnd, &rect);
const INT win_width{ rect.right - rect.left };
const INT win_height{ rect.bottom - rect.top };
在繪圖之前,我還調用了 SetProcessDPIAware()。
根據@Paul Sanders 的反饋,我重寫了我的 paintDoubleBuffered 方法如下,注意,我在 object 構造函數中調用了 BufferedPaintInit :
void MainWindow::paintDoubleBuffered(HWND hwnd) {
PAINTSTRUCT ps;
HDC hdc{ BeginPaint(hwnd, &ps)};
RECT sz;
GetWindowRect(hwnd, &sz);
BP_PAINTPARAMS paintParams = { 0 };
paintParams.cbSize = sizeof(paintParams);
paintParams.dwFlags = BPPF_ERASE;
paintParams.pBlendFunction = NULL;
paintParams.prcExclude = NULL;
HDC hdcBuffer;
HPAINTBUFFER hBufferedPaint = BeginBufferedPaint(hdc, &sz, BPBF_COMPATIBLEBITMAP, &paintParams, &hdcBuffer);
if (hBufferedPaint && this->bufferedInitResult == Ok) {
// Application specific painting code
paint(hwnd, hdcBuffer);
EndBufferedPaint(hBufferedPaint, TRUE);
}
else{
paint(hwnd, hdc);
}
ReleaseDC(hwnd, hdc);
}
問題最終不是雙緩沖的方法,而是在我的繪畫方法中對Graphics::DrawImage(Image*, Gdiplus::Point)
的調用。 更改為DrawImage(Image* image, INT x, INT y, INT width, INT height)
解決了縮放問題。
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