Background changes after images are drawn on the screen - c++

Question

We are learning about windows raw touch events in class using Visual Studios 2012 in C++. I got my demo working and it does exactly what it is supposed to, which is drawing circles beneath your fingertips to detect that a touch event has been raised. But after a certain time has passed and if you are still pressing on the screen with the circles drawn the screen turns blue! The circles still show but they are blue as well with black contours and I can still move them around. I showed the professor and he can't seem to figure it out which is why I came here. Can anyone take a look at my code to let me know what seems to be the cause of it?
// GT_HelloWorldWin32.cpp
// compile with: /D_UNICODE /DUNICODE /DWIN32 /D_WINDOWS /c
#ifndef WINVER // Specifies that the minimum required platform is Windows 7.
#define WINVER 0x0601 // Change this to the appropriate value to target other versions of Windows.
#endif
#ifndef _WIN32_WINNT // Specifies that the minimum required platform is Windows 7.
#define _WIN32_WINNT 0x0601 // Change this to the appropriate value to target other versions of Windows.
#endif
#include <windows.h> // for windows touch
#include <windowsx.h> // included for point conversion
#include <stdlib.h>
#include <string.h>
#include <tchar.h>
#include "wtypes.h"
#include <iostream>
using namespace std;
// The main window class name.
TCHAR szWindowClass[] = _T("win32app");
// The string that appears in the application's title bar.
TCHAR szTitle[] = _T("Hello World!");
//Instancing the handler
HINSTANCE hInst;
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
//Maximum ammount of touches allowed
#define MAXPOINTS 10
// You will use this array to track touch points
int points[MAXPOINTS][2];
// You will use this array to switch the color / track ids
int idLookup[MAXPOINTS];
// You can make the touch points larger
// by changing this radius value
static int radius = 30;
// There should be at least as many colors
// as there can be touch points so that you
// can have different colors for each point
COLORREF colors[] = { RGB(153,255,51),
RGB(153,0,0),
RGB(0,153,0),
RGB(255,255,0),
RGB(255,51,204),
RGB(0,0,0),
RGB(0,153,0),
RGB(153, 255, 255),
RGB(153,153,255),
RGB(0,51,153)
};
int wmId, wmEvent, i, x, y, index;
UINT cInputs;
PTOUCHINPUT pInputs;
POINT ptInput;
// This function is used to return an index given an ID
int GetContactIndex(int dwID){
for (int i=0; i < MAXPOINTS; i++){
if (idLookup[i] == -1){
idLookup[i] = dwID;
return i;
}else{
if (idLookup[i] == dwID){
return i;
}
}
}
// Out of contacts
return -1;
}
int WINAPI WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
WNDCLASSEX wcex;
int width = 0, height = 0; // Screen resolution
GetScreenResolution(width, height);
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = NULL;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
if (!RegisterClassEx(&wcex))
{
MessageBox(NULL,
_T("Call to RegisterClassEx failed!"),
_T("Win32 Guided Tour"),
NULL);
return 1;
}
hInst = hInstance; // Store instance handle in our global variable
// The parameters to CreateWindow explained:
// szWindowClass: the name of the application
// szTitle: the text that appears in the title bar
// WS_OVERLAPPEDWINDOW: the type of window to create
// CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
// 500, 100: initial size (width, length)
// NULL: the parent of this window
// NULL: this application does not have a menu bar
// hInstance: the first parameter from WinMain
// NULL: not used in this application
HWND hWnd = CreateWindow(
szWindowClass,
szTitle,
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT,
800, 600,
NULL,
NULL,
hInstance,
NULL
);
if (!hWnd) {
MessageBox(NULL,
_T("Call to CreateWindow failed!"),
_T("Win32 Guided Tour"),
NULL);
return 1;
}
// register the window for touch instead of gestures
RegisterTouchWindow(hWnd, 0);
// the following code initializes the points
for (int i=0; i< MAXPOINTS; i++){
points[i][0] = -1;
points[i][1] = -1;
idLookup[i] = -1;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
// Main message loop:
MSG msg;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int) msg.wParam;
}
//
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes touch messages for the main window.
//
// WM_TOUCH - handles WM_TOUCH messages in the application
// WM_DESTROY - post a quit message and return
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
// For double buffering
static HDC memDC = 0;
static HBITMAP hMemBmp = 0;
HBITMAP hOldBmp = 0;
//For drawing / fills
PAINTSTRUCT ps;
HDC hdc;
switch (message)
{
case WM_TOUCH:
//LOWORD(wParam) = number of touch points in this message
//HIWORD(wParam) = reserved for future use
//lParam = handle for use with GetTouchInputInfo
cInputs = LOWORD(wParam);
pInputs = new TOUCHINPUT[ cInputs ];
if(pInputs)
{
if( GetTouchInputInfo((HTOUCHINPUT)lParam, cInputs, pInputs, sizeof(TOUCHINPUT)) )
{
for (int i=0; i < static_cast<INT>(cInputs); i++)
{
TOUCHINPUT ti = pInputs[i];
index = GetContactIndex(ti.dwID);
if(ti.dwID != 0 && index < MAXPOINTS )
{
//get screen corrdinates of touch
ptInput.x = TOUCH_COORD_TO_PIXEL(ti.x);
ptInput.y = TOUCH_COORD_TO_PIXEL(ti.y);
//get coordinates relative to the top left of the application window
ScreenToClient(hWnd, &ptInput);
if(ti.dwFlags & TOUCHEVENTF_UP)
{
points[index][0] = -1;
points[index][1] = -1;
}
else
{
points[index][0] = ptInput.x;
points[index][1] = ptInput.y;
}
}
}
}
CloseTouchInputHandle((HTOUCHINPUT)lParam);
delete [] pInputs;
}
InvalidateRect(hWnd, NULL, FALSE);
break;
case WM_PAINT:
hdc = BeginPaint(hWnd, &ps);
RECT client;
GetClientRect(hWnd, &client);
//START DOUBLE BUFFERING
if (!memDC)
{
memDC = CreateCompatibleDC(hdc);
}
hMemBmp = CreateCompatibleBitmap(hdc, client.right, client.bottom);
hOldBmp = (HBITMAP)SelectObject(memDC, hMemBmp);
FillRect(memDC, &client, CreateSolidBrush(RGB(255,255,255)));
//Draw Touched Points
for (i=0; i < MAXPOINTS; i++)
{
SelectObject( memDC, CreateSolidBrush(colors[i]));
x = points[i][0];
y = points[i][1];
if (x >0 && y>0)
{
Ellipse(memDC, x - radius, y - radius, x + radius, y + radius);
}
}
BitBlt(hdc, 0,0, client.right, client.bottom, memDC, 0,0, SRCCOPY);
EndPaint(hWnd, &ps);
ReleaseDC(hWnd, hdc);
//DeleteObject(hMemBmp);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}

Answer 1

I see the problem now. You have a GDI resource leak.
In two places you call CreateSolidBrush but you never delete the brushes you created. You do it here
FillRect(memDC, &client, CreateSolidBrush(RGB(255,255,255)));
and here
SelectObject( memDC, CreateSolidBrush(colors[i]));
Really, you should assign the result of eachCreateSolidBrush function to a HBRUSH and then call DeleteObject on it when you've finished with it.
You also need to release your bitmap: DeleteObject(hMemBmp) which you have commented out and also remove the call to ReleaseDC as I said in the comments.
Generally, you should keep a careful track of all of the GDI objects you have created and make sure you delete them when you've finished with them.