Referencing MFC, the win32 AwtGraphics::FillRect() performance can be improved by using the following API calls

AwtGraphics::FillRect(...)
{
    // ...
    ::SetBkColor(m_hDC, clr);
    ::ExtTextOut(m_hDC, 0, 0, ETO_OPAQUE, lpRect, NULL, 0, NULL);
    // ...
}

Instead of the current coding,

void AwtGraphics::FillRect(JNIEnv* env, long nX, long nY, long nW, long nH)
{
    if (nW <= 0 || nH <= 0) {
        return;
    }
    HDC hDC = GetDC();
    if (hDC == NULL) {
        return;
    }
    SetBrushColor(TRUE);
    // Bug #4047723 (FillRect apears wrong (was using the wrong DC handle))
    // Bug #4055623 (Performance enhancements)
    VERIFY(::PatBlt(hDC, nX + m_originX, nY + m_originY, nW, nH,
                    ((m_rop == R2_XORPEN) ? PATINVERT : PATCOPY)));
    ReleaseDC();
}