Unable to update window in consol application

Question

I am extending an old console application. Trying to add a window( for an animation ). Are able to display first image, but unable to update the window with later images. Have created a minimum application to demonstrate the problem. In this app I have a red window that should change at each update of the window( it is not ). What am I doing wrong ?

#include "pch.h"
#include <iostream>
#include <Windows.h>

using namespace std;

HWND hWindow;   

LRESULT __stdcall MyWindowProcedure(HWND hWnd, unsigned int msg, WPARAM wp, LPARAM lp)
{
    PAINTSTRUCT ps;
    HDC hdc;
    HBITMAP hBitmap;
    VOID * pvBits;
    RGBQUAD  *bmiColors;
    static int j = 128;
    HBITMAP hOldBmp;
    BITMAPINFO MyBitmap;
    BOOL qRetBlit;


    switch (msg)
    {

    case WM_DESTROY:
        std::cout << "\ndestroying window\n";
        PostQuitMessage(0);
        return 0L;

    case WM_LBUTTONDOWN:
        std::cout << "\nmouse left button down at (" << LOWORD(lp)
            << ',' << HIWORD(lp) << ")\n";
        // fall thru

    case WM_PAINT:

        hdc = BeginPaint(hWnd, &ps);
#if 1
        // Create a device context that is compatible with the window
        HDC hLocalDC;
        hLocalDC = ::CreateCompatibleDC(hdc);
        // Verify that the device context was created
        if (hLocalDC == NULL) {
            printf("CreateCompatibleDC Failed\n");
            //          return false;
            break;
        }

        MyBitmap.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
        MyBitmap.bmiHeader.biWidth = 256;
        MyBitmap.bmiHeader.biHeight = -256;
        MyBitmap.bmiHeader.biPlanes = 1;
        MyBitmap.bmiHeader.biBitCount = 32;
        MyBitmap.bmiHeader.biCompression = BI_RGB;
        MyBitmap.bmiHeader.biSizeImage = 256 * 256 * 4;
        MyBitmap.bmiHeader.biYPelsPerMeter = 1000;
        MyBitmap.bmiHeader.biXPelsPerMeter = 1000;
        MyBitmap.bmiHeader.biClrUsed = 0;
        MyBitmap.bmiHeader.biClrImportant = 0;

        hBitmap = CreateDIBSection(NULL, &MyBitmap, DIB_RGB_COLORS, &pvBits, NULL, NULL);
        bmiColors = (RGBQUAD*)pvBits;

        // note: BGR
        for (int i = 0; i < 256 * 256; i++)
        {
            bmiColors[i].rgbBlue = 0;
            bmiColors[i].rgbGreen = 0;
            bmiColors[i].rgbRed = j % 256;
            bmiColors[i].rgbReserved = 255;
        }
        j += 10;

        bmiColors[1000].rgbRed;

        // Select the bitmap into the device context
        hOldBmp = (HBITMAP)::SelectObject(hLocalDC, hBitmap);
        if (hOldBmp == NULL) {
            printf("SelectObject Failed");
            //          return false;
            break;
        }

        // Blit the dc which holds the bitmap onto the window's dc
        qRetBlit = ::BitBlt(hdc, 0, 0, 256, 256, hLocalDC, 0, 0, SRCCOPY);
        if (!qRetBlit) {
            printf("Blit Failed");
            //          return false;
            break;
        }

        // Unitialize and deallocate resources
        SelectObject(hLocalDC, hOldBmp);
        DeleteDC(hLocalDC);
        DeleteObject(hBitmap);
#endif
        EndPaint(hWnd, &ps);
        break;

    default:

        std::cout << '.';
        break;
    }
    return DefWindowProc(hWnd, msg, wp, lp);
}

int main()

{
    WNDCLASSEX wndclass = { sizeof(WNDCLASSEX), CS_DBLCLKS | CS_HREDRAW, MyWindowProcedure,
                                0,  0, GetModuleHandle(0), LoadIcon(0,IDI_APPLICATION),
                                LoadCursor(0,IDC_ARROW), HBRUSH(COLOR_WINDOW + 1),
                                0, L"myclass", LoadIcon(0,IDI_APPLICATION) };

    if (RegisterClassEx(&wndclass))
    {
        hWindow = CreateWindowEx(0, L"myclass", L"myclass", WS_OVERLAPPEDWINDOW, 1200, 600, 256 + 15, 256 + 38, 0, 0, GetModuleHandle(0), 0);

        ShowWindow(hWindow, SW_SHOWDEFAULT);
        UpdateWindow(hWindow);

        MSG msg;
        byte bRet;

        while ((bRet = GetMessage(&msg, hWindow, 0, 0)) != 0)
        {
            if (bRet == -1)
            {
                return 1;
            }
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
    }
}

You should not call [BeginPaint](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-beginpaint) except in response to a WM_PAINT message, and every call to `BeginPaint` must be matched with a call to `EndPaint`. — 1201ProgramAlarm, Dec 03 '19 at 19:21
So the error is in the "missing" break in the case WM_LBUTTONDOWN: std::cout << "\nmouse left button down at (" << LOWORD(lp) << ',' << HIWORD(lp) << ")\n"; // fall thru — enocknitti, Dec 03 '19 at 19:35
So BeginPaint() and EndPaint(); can only be used as a responce to WM_PAINT: Is that correct ? — enocknitti, Dec 03 '19 at 19:40
Ok that seems to be the problem. Then I have to update the image by som othe way than "fall thru" on the WM_LBUTTONDOWN btw: I found that code in some example on the net. I will try to find that example again and add a commet about this. — enocknitti, Dec 03 '19 at 19:59
On a side note, get rid of the check for `if (hOldBmp == NULL)` after the call to `::SelectObject(hLocalDC, hBitmap)`. And since the `HBITMAP` is not dependent on anything that is not known until `WM_PAINT` is processed, you should just create the `HBITMAP` when the window is first created (in `WM_CREATE`), re-use it every time `WM_PAINT` is received, and then destroy it in `WM_DESTROY`. — Remy Lebeau, Dec 03 '19 at 22:03

lakeweb · Accepted Answer · 2019-12-03T22:20:36.340

1

As pointed out. You do not want to call WM_PAINT your self. Let the system handle it. So in WM_LBUTTONDOWN do:

case WM_LBUTTONDOWN:
        std::cout << "\nmouse left button down at (" << LOWORD(lp)
            << ',' << HIWORD(lp) << ")\n";
        InvalidateRect(hWnd, nullptr, FALSE);
        return 0;

Do not fall through. Wnen you call RedrawWindow the window is invalidated and then needs to be repainted. I just tested this, the window lightens up on each click.

UPDATE: Thanks to Remy Lebeau

Difference between InvalidateRect and RedrawWindow

And yes, it is better to let windows use its own schedule for this kind of stuff.

edited Dec 03 '19 at 22:20

answered Dec 03 '19 at 20:03

lakeweb

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Unless you need an immediate repaint, you should generally use `InvalidateRect()` instead and let the OS generate `WM_PAINT` on its own time when appropriate – Remy Lebeau Dec 03 '19 at 22:05
@Remy Lebeau, thanks. I work with MFC and have rarely used a console method. I did not find `Invalidate()` for this. I'll update my post. – lakeweb Dec 03 '19 at 22:13
[`InvalidateRect()`](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-invalidaterect) – Remy Lebeau Dec 03 '19 at 22:19

Unable to update window in consol application

1 Answers1