Method AveragePixelArea

ColorCop/ColorCopDlg.cpp:2718–2774

Compute the average RGB value of a square region centered on `point`.

// Compute the average RGB value of a square region centered on `point`.
bool CColorCopDlg::AveragePixelArea(HDC hdc, int* m_R, int* m_G, int* m_B, CPoint point) {
    // Compute the average RGB value of a square region centered on `point`.
    // The region size is (2 * m_iSamplingOffset + 1) on each side.
    int64_t reddec = 0, greendec = 0, bluedec = 0;  // 64-bit to safely accumulate many pixel values
    int offset = m_iSamplingOffset;
    int elements = 0;  // count only valid pixels

    COLORREF crefxy;
    int xrel, yrel;

    // Compute unclamped bounds
    int xmin = point.x - offset;
    int ymin = point.y - offset;

    // Clamp lower bounds manually (avoids std::max(int, uint16_t) ambiguity)
    if (xmin < 0)
        xmin = 0;
    if (ymin < 0)
        ymin = 0;

    // Walk the sampling region and accumulate RGB components.
    for (xrel = xmin; xrel <= point.x + offset; xrel++) {
        for (yrel = ymin; yrel <= point.y + offset; yrel++) {
            crefxy = ::GetPixel(hdc, xrel, yrel);

            // Skip invalid pixels; GetPixel can fail near screen edges or on invalid DCs.
            if (crefxy == CLR_INVALID)
                continue;

            reddec += GetRValue(crefxy);
            greendec += GetGValue(crefxy);
            bluedec += GetBValue(crefxy);
            ++elements;  // count only valid samples
        }
    }

    if (elements == 0) {
        // No valid pixels sampled; treat as unchanged.
        return true;
    }

    // Convert accumulated totals into average RGB values.
    reddec /= elements;
    greendec /= elements;
    bluedec /= elements;

    // Check whether the averaged color differs from the previously stored sample.
    // This avoids unnecessary updates when the sampled color hasn't changed.
    if (reddec != m_Reddec || greendec != m_Greendec || bluedec != m_Bluedec) {
        *m_R = static_cast<int>(reddec);
        *m_G = static_cast<int>(greendec);
        *m_B = static_cast<int>(bluedec);
        return false;  // color changed
    }

    return true;  // color unchanged
}