此代码在两个线程中从窗口的顶部到底部绘制两条垂直条纹(每个线程的相应函数为thread_func
)。第一个线程绘制左边条纹的一部分,然后第二个线程绘制右边的一部分,然后再绘制第一个,依此类推。信号量和关键部分用于确保此顺序。
#include <windows.h>
#include <cstdint>
HDC hDC;
HDC hDCMem;
HBITMAP hbitmap;
HWND hwnd;
int ScreenMaxX;
int ScreenMaxY;
short pattern[8]={~0xFF, ~0xFF, ~0xFF, ~0xFF, ~0xFF, ~0xFF, ~0xFF, ~0xFF};
HBRUSH brush=::CreatePatternBrush(::CreateBitmap(8, 8, 1, 1, pattern));
void bar(int nLeft, int nTop, int nRight, int nBottom)
{
RECT rect;
rect.left = nLeft;
rect.right = nRight;
rect.top = nTop;
rect.bottom = nBottom;
::SetTextColor(hDCMem, 0xFF00FF);
::SetBkColor(hDCMem, 0xFF00FF);
//brush=::CreatePatternBrush(::CreateBitmap(8, 8, 1, 1, pattern));
::FillRect(hDCMem, &rect, brush);
}
void flush(){
::BitBlt(hDC, 0, 0, ScreenMaxX, ScreenMaxY, hDCMem, 0, 0, SRCCOPY);
}
CRITICAL_SECTION graphics_cs;
uint8_t thread_cnt=0;
uint8_t total_threads=2;
HANDLE turnstile1=CreateSemaphoreW(nullptr, 0, 2, nullptr);
void thread_func(int num){
int x,y;
if(num==0){
x=20; y=0;
} else {
x=110; y=0;
}
while(true) {
while(true) {
EnterCriticalSection(&graphics_cs);
if (thread_cnt == num) {
thread_cnt++;
bar(x, y, x+40, y+40);
y+=1;
//flush();
if(thread_cnt==total_threads){
thread_cnt = 0;
flush();
ReleaseSemaphore(turnstile1, total_threads, nullptr);
}
LeaveCriticalSection(&graphics_cs);
break;
} else {
LeaveCriticalSection(&graphics_cs);
}
}
WaitForSingleObject(turnstile1, INFINITE);
Sleep(100);
}
}
void mainx ()
{
InitializeCriticalSection(&graphics_cs);
for(int i=0; i<total_threads; i++){
CreateThread (nullptr, 0, (LPTHREAD_START_ROUTINE)thread_func, (LPVOID)i, 0, nullptr);
}
}
DWORD Th(LPVOID param)
{
(void)param;
::SetWindowPos(hwnd, HWND_TOP,
10,
10,
400,
500,
SWP_SHOWWINDOW
);
mainx();
flush();
return 0;
}
DWORD g_nMainThreadID;
//processing main window messages
long FAR PASCAL WindowProc(HWND hWnd,UINT message, WPARAM wParam,LPARAM lParam )
{
switch (message)
{
case WM_PAINT: flush();
break;
case WM_DESTROY: PostQuitMessage(0);
break;
}
return DefWindowProc(hWnd, message, wParam, lParam);
}
int PASCAL WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd )
{
(void)hPrevInstance, (void)lpCmdLine;
WNDCLASS wc;
MSG msg;
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = WindowProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = NULL;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
wc.lpszMenuName = "Menu_one";
wc.lpszClassName = "NAME";
if (!RegisterClass(&wc)) {return 0; };
//main window
hwnd = CreateWindow("NAME",
"!",
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
HWND_DESKTOP,
NULL,
hInstance,
NULL
);
ScreenMaxX = ::GetSystemMetrics(SM_CXSCREEN);
ScreenMaxY = ::GetSystemMetrics(SM_CYSCREEN);
hDC = ::GetDC(hwnd);
hDCMem = ::CreateCompatibleDC(hDC);
hbitmap = ::CreateCompatibleBitmap(hDC, ScreenMaxX, ScreenMaxY );
::SelectObject(hDCMem, hbitmap);
auto hbrush = (HBRUSH)::GetStockObject(WHITE_BRUSH);
::SelectObject(hDCMem, hbrush);
::PatBlt(hDCMem, 0,0, ScreenMaxX, ScreenMaxY, PATCOPY );
::DeleteObject(hbrush);
CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)Th, (LPVOID)hwnd, 0,&g_nMainThreadID);
ShowWindow(hwnd, nShowCmd);
UpdateWindow(hwnd);
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;
}
在Windows 7中,条纹以与预期相同的速度绘制。但在Windows XP中,速度是不同的:
如果我取消注释//brush=::CreatePatternBrush(::CreateBitmap(8, 8, 1, 1, pattern));
或//flush();
行,则Windows XP中的绘图速度将相同。为什么这会解决问题,为什么初始代码的行为在不同版本的Windows中会有所不同?
更新
当我在std::cout<<"num = "<<num<<" : bar call\n";
中的std::cout<<"num = "<<num<<" : flush call\n";
和bar
来电之后添加flush
和thread_func
时,输出为
num = 0 : bar call
num = 1 : bar call
num = 1 : flush call
num = 0 : bar call
num = 1 : bar call
num = 1 : flush call
num = 0 : bar call
num = 1 : bar call
num = 1 : flush call
num = 0 : bar call
num = 1 : bar call
num = 1 : flush call
...
订单似乎是正确的,但在刷新调用后不会立即绘制左边的条纹。
答案 0 :(得分:1)
从我的评论中抽取一些答案。
请注意,GDI会对可能导致较慢计算机上的突发呈现的操作进行批处理。虽然GDI在XP和7上都进行了批量处理,但实际上这在7上似乎不再是一个问题。尝试调用GdiSetBatchLimit将限制设置为1.这将导致GDI在每次调整后刷新呼叫,总体上可能较慢,但应消除突发行为。