C++中扫描内存位图特定RGB像素并获取坐标的问题

Hey there! Let's figure out why your red=60 pixel search is returning wonky results. Based on what you've shared, these are the most common pitfalls and fixes to get accurate x/y coordinates:

1. You're Using RGB Order Instead of BGR #

Windows GDI bitmaps store pixel data in BGR order (blue first, green middle, red last) by default—this is a super easy mistake to make! If you're checking the first byte of a pixel as red, you're actually looking at blue. Here's how to correctly extract the red channel:

// Assuming you have a pointer to your bitmap's raw bits (BYTE* pBits)
// And you've calculated the correct pitch (stride) of the bitmap
int pixelOffset = (y * pitch) + (x * 3); // For 24-bit color (3 bytes per pixel)

BYTE blue = pBits[pixelOffset];
BYTE green = pBits[pixelOffset + 1];
BYTE red = pBits[pixelOffset + 2]; // This is the actual red value!

if (red == 60) {
    // Found your target pixel—return x and y here
    return true;
}

2. Ignoring Bitmap Pitch/Stride Alignment #

Bitmap rows are padded to the nearest 4-byte boundary by Windows, so the pitch (stride) isn't just width * 3 for 24-bit images. If you skip this alignment, you'll read off-byte data and get incorrect color values. Here's how to calculate the correct pitch:

BITMAPINFO bmi = {0};
bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth = w;
bmi.bmiHeader.biHeight = h;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 24; // 24-bit color (no alpha)
bmi.bmiHeader.biCompression = BI_RGB;

// Calculate aligned pitch
int pitch = (w * 3 + 3) & ~3; // Rounds up to next multiple of 4
int bitmapSize = pitch * h;

BYTE* pBits = new BYTE[bitmapSize];
// Extract bits from your captured bitmap
GetDIBits(hdcSource, hBitmap, 0, h, pBits, &bmi, DIB_RGB_COLORS);

3. Misaligned Capture Coordinates #

Double-check that the x,y,w,h parameters you're passing to findColor are relative to the window's client area (not screen coordinates). If you're using screen coordinates, convert them with ScreenToClient:

POINT screenPos = {x, y};
ScreenToClient(window, &screenPos);
// Use screenPos.x and screenPos.y for your BitBlt or GetDIBits call

4. Incomplete Bitmap Capture Cleanup #

If you don't properly select the original bitmap back into the memory DC before cleaning up, you might corrupt your bitmap data. Make sure your capture code follows this flow:

HWND window = FindWindowA(NULL, "windownamehere");
HDC hdcWindow = GetDC(window);
HDC hdcMem = CreateCompatibleDC(hdcWindow);
HBITMAP hBitmap = CreateCompatibleBitmap(hdcWindow, w, h);
HBITMAP hOldBitmap = (HBITMAP)SelectObject(hdcMem, hBitmap);

// Copy window content to memory DC
BitBlt(hdcMem, 0, 0, w, h, hdcWindow, x, y, SRCCOPY);

// Extract bits and search for color here...

// Critical cleanup steps
SelectObject(hdcMem, hOldBitmap); // Re-select original bitmap
DeleteDC(hdcMem);
ReleaseDC(window, hdcWindow);
DeleteObject(hBitmap);

Putting it all together, your corrected findColor function should account for BGR order, aligned pitch, and proper coordinate handling. That should fix those unexpected results!

内容的提问来源于stack exchange，提问作者Billy Penley