Question

I don’t know what title should I use, but please read this.

I’m making an program that displays the color at the mouse pointer location. I want to use WM_INPUT because WM_MOUSEMOVE is not update quickly enough.

Here’s some of my main code.

#include <Windows.h>
#include <WindowsX.h>

/* void Cls_OnInput(HWND hWnd, UINT inputCode, HRAWINPUT hRawInput) */
#define HANDLE_WM_INPUT(hWnd, wParam, lParam, fn) \
  ((fn)((hWnd), GET_RAWINPUT_CODE_WPARAM(wParam), (HRAWINPUT)(lParam)), 0L)

static LPCTSTR main_window_class_name = TEXT("MainWindow");
static HDC hdc_screen;
static COLORREF color;

LRESULT CALLBACK MainWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
BOOL MainWindow_OnCreate(HWND hWnd, LPCREATESTRUCT lpCreateStruct);
void MainWindow_OnDestroy(HWND hWnd);
void MainWindow_OnPaint(HWND hWnd);
void MainWindow_OnInput(HWND hWnd, UINT inputCode, HRAWINPUT hRawInput);

ATOM RegisterMainWindowClass(HINSTANCE hInstance)
{
  WNDCLASSEX wcex;

  wcex.cbSize = sizeof(wcex);
  wcex.style = 0;
  wcex.lpfnWndProc = MainWindowProc;
  wcex.cbClsExtra = 0;
  wcex.cbWndExtra = 0;
  wcex.hInstance = hInstance;
  wcex.hIcon = (HICON)LoadImage(NULL, IDI_APPLICATION, IMAGE_ICON, 0, 0, LR_SHARED);
  wcex.hCursor = (HCURSOR)LoadImage(NULL, IDC_ARROW, IMAGE_CURSOR, 0, 0, LR_SHARED);
  wcex.hbrBackground = GetSysColorBrush(COLOR_BTNFACE);
  wcex.lpszMenuName = NULL;
  wcex.lpszClassName = main_window_class_name;
  wcex.hIconSm = wcex.hIcon;

  return RegisterClassEx(&wcex);
}

HWND CreateMainWindow(HINSTANCE hInstance)
{
  return CreateWindow(main_window_class_name, TEXT("WhatColor"), WS_CAPTION | WS_SYSMENU, CW_USEDEFAULT, CW_USEDEFAULT, 640, 480, HWND_DESKTOP, NULL, hInstance, NULL);
}

LRESULT CALLBACK MainWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
  switch (uMsg)
  {
    HANDLE_MSG(hWnd, WM_CREATE, MainWindow_OnCreate);
    HANDLE_MSG(hWnd, WM_DESTROY, MainWindow_OnDestroy);
    HANDLE_MSG(hWnd, WM_PAINT, MainWindow_OnPaint);
    HANDLE_MSG(hWnd, WM_INPUT, MainWindow_OnInput);
  default:
    return DefWindowProc(hWnd, uMsg, wParam, lParam);
  }
}

BOOL MainWindow_OnCreate(HWND hWnd, LPCREATESTRUCT lpCreateStruct)
{
  RAWINPUTDEVICE rid[1];

  UNREFERENCED_PARAMETER(lpCreateStruct);

  rid[0].usUsagePage = 1;
  rid[0].usUsage = 2;
  rid[0].dwFlags = 0;
  rid[0].hwndTarget = hWnd;
  RegisterRawInputDevices(rid, 1, sizeof(rid[0]));

  hdc_screen = CreateDC(TEXT("DISPLAY"), NULL, NULL, NULL);

  return TRUE;
}

void MainWindow_OnDestroy(HWND hWnd)
{
  UNREFERENCED_PARAMETER(hWnd);

  DeleteDC(hdc_screen);
  PostQuitMessage(EXIT_SUCCESS);
}

void MainWindow_OnPaint(HWND hWnd)
{
  static PAINTSTRUCT ps;

  BeginPaint(hWnd, &ps);
  EndPaint(hWnd, &ps);
}

void MainWindow_OnInput(HWND hWnd, UINT inputCode, HRAWINPUT hRawInput)
{
  static RAWINPUT raw_input;
  static UINT raw_input_size = sizeof(raw_input);
  static POINT point;

  UNREFERENCED_PARAMETER(inputCode);

  GetRawInputData(hRawInput, RID_HEADER, &raw_input, &raw_input_size, sizeof(raw_input.header));

  if (raw_input.header.dwType == RIM_TYPEMOUSE)
  {
    GetCursorPos(&point);
    color = GetPixel(hdc_screen, point.x, point.y);
    DeleteBrush(SetClassLong(hWnd, GCL_HBRBACKGROUND, (LONG)CreateSolidBrush(color)));
    InvalidateRect(hWnd, NULL, TRUE);
  }
}

The problem is the program seems to process WM_INPUT message again and again, and the main window is stuck. If I remove

color = GetPixel(hdc_screen, point.x, point.y);

the window is normal, but I can’t get the color I want.

I think it’s better if you try to test my code.

What should I do to fix this?

Answer 1

I’ll use Timer and process WM_TIMER message instead.