Thread: Lagged GDI paint. can't find source of problem

I'm working on a networked paint program which is starting to work fine, except that after a paint command is sent to the server and the server echos it back, there is a a 10-30 second lag in the program, then it goes back to normal. Does anyone know what might be causing this? There is a lot of code, so I have only posted select pieces. The lag occurs after the command is received and drawn, but I don't see what the program is doing after that, where the lag could come from.


This is the process which handles all the socket programming. I'm working with a winsock wrapper class to handle all network programming (of which I've worked through and tested and am positive works fine).

Code:

LRESULT WINAPI TopDlgProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{

	//socket activity on the server half of the program.
	if (uMsg == perServer.getEvent())
	{
		nEventCode = WSAGETSELECTEVENT(lParam);
		nErrorCode = WSAGETSELECTERROR(lParam);
		switch (nEventCode)
		{
			case FD_READ:
				ZeroMemory(crchat, 1024);

				lstUser.reset();
				while (lstUser.next()) {
					if (lstUser.getData().getSocket() == (SOCKET)wParam) break;
				}
				lstUser.getData().perReadLine(crchat, 1024, "DELIMITER");

				perServer.perSend(crchat, 1024, lstUser.getData().getSocket());

				//lstUser.reset();
				//while (lstUser.next()) {
				//	perServer.perSend(crchat, 1024, lstUser.getData().getSocket());
				//}

				return false;
				break;
			case FD_WRITE:
				return false;
				break;
			case FD_ACCEPT:
				lstUser.insert(perServer.perAccept());
				AppendChatBuff("[Server] User Connected!");
				return false;
				break;
			case FD_CLOSE:
				AppendChatBuff("[Server] User Left!");
				return false;
				break;
			default:
				return false;
				break;
		}
	}

	//occurs when socket activity occurs on client
	if (uMsg == perClient.getEvent())
	{
		nEventCode = WSAGETSELECTEVENT(lParam);
		nErrorCode = WSAGETSELECTERROR(lParam);
		switch (nEventCode)
		{
			case FD_READ:
				ZeroMemory(crchat, 1024);
				perClient.perReadLine(crchat, 1024, "DELIMITER");
				DecodeMessage(crchat, 1024);
				break;
			case FD_WRITE:
				break;
			case FD_CONNECT:
				if (nErrorCode)
				{
					perClient.perClose();
					AppendChatBuff("[Client] Connection failed!");
					break;
				}
				AppendChatBuff("[Client] Connected!");
				break;
			case FD_CLOSE:
				perClient.perClose();
				AppendChatBuff("[Client] Disconnected!");
				break;
			default:
				break;
		}
	}

Here is the canvas dialog process, in which everything is painted.

Code:

LRESULT WINAPI CanvasDlgProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam){
	switch(uMsg)
	{
	case WM_LBUTTONDOWN:
		if (GetForegroundWindow() != hDlgCanvas) return false;
		crDrawing.pStart.x = LOWORD(lParam);
		crDrawing.pStart.y = HIWORD(lParam);
		crDrawing.LineWidth = 5;
		crDrawing.cRed = GetRValue(crForeground);
		crDrawing.cBlue = GetBValue(crForeground);
		crDrawing.cGreen = GetGValue(crForeground);
		if (crDrawing.ToolID == PIXELBRUSH)
		{
			crDrawing.MakePacket();
			perClient.perSend(crDrawing.szPacket, 17);
		}
		break;
	case WM_LBUTTONUP:
		if (GetForegroundWindow() != hDlgCanvas) return false;
		crDrawing.pEnd.x = LOWORD(lParam);
		crDrawing.pEnd.y = HIWORD(lParam);
		crDrawing.MakePacket();
		perClient.perSend(crDrawing.szPacket, 17);
		break;
	case WM_MOUSEMOVE:
		if (GetForegroundWindow() != hDlgCanvas) return false;
		if ((wParam == MK_LBUTTON) && (crDrawing.ToolID == PIXELBRUSH))
		{
			crDrawing.pStart.x = LOWORD(lParam);
			crDrawing.pStart.y = HIWORD(lParam);
			crDrawing.LineWidth = 5;
			crDrawing.cRed = GetRValue(crForeground);
			crDrawing.cBlue = GetBValue(crForeground);
			crDrawing.cGreen = GetGValue(crForeground);	
			crDrawing.MakePacket();
			perClient.perSend(crDrawing.szPacket, 17);
		}
	case WM_CTLCOLORDLG:
		HBRUSH hbrTemp;
		hbrTemp = CreateSolidBrush(RGB(255, 255, 255));
		return (LRESULT)hbrTemp;
		break;
	case WM_DESTROY:
		break;
	}
	return false;
}

Here is the function which recieves a command to draw an object and then draws it accordingly. I know it's a bad idea to create an HDC everytime, but I changed it to this way to try and isolate the problem. Even when hdcCanvas was a global (and hPen as well), it still did the lagging.

Code:

void DrawObj(CPaintTool crPaintTool)
{
	HDC hdcCanvas = GetDC(hDlgCanvas);
	COLORREF crColor = RGB(crPaintTool.cRed, crPaintTool.cGreen, crPaintTool.cBlue);
	HPEN hPen = CreatePen(PS_SOLID, crPaintTool.LineWidth, crColor);
	SelectObject(hdcCanvas, (HGDIOBJ)hPen);

	switch (crPaintTool.ToolID)
	{
	case PIXELBRUSH:
		MoveToEx(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pStart.y, NULL);
		LineTo(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pStart.y);
		break;

	case LINE:
		MoveToEx(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pStart.y, NULL);
		LineTo(hdcCanvas, crPaintTool.pEnd.x, crPaintTool.pEnd.y);
		break;

	case RECTANGLE:
		MoveToEx(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pStart.y, NULL);
		LineTo(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pEnd.y);
		LineTo(hdcCanvas, crPaintTool.pEnd.x, crPaintTool.pEnd.y);
		LineTo(hdcCanvas, crPaintTool.pEnd.x, crPaintTool.pStart.y);
		LineTo(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pStart.y);
		break;

	case CIRCLE:
		Ellipse(hdcCanvas, crPaintTool.pStart.x, crPaintTool.pStart.y, crPaintTool.pEnd.x, crPaintTool.pEnd.y);
		break;

	default:
		break;
	}
	DeleteObject(hPen);
	ReleaseDC(hDlgCanvas, hdcCanvas);
	DeleteDC(hdcCanvas);
}

I can't even trace where the lag is comming from. Doing a debug and stepping through leads me nowhere. I appreciate time taken to look through this.