c++ basic GDI bitmap not working

VooDooChicken 40 Reputation points
2024-10-02T04:43:50.6+00:00

hi, I want to draw a bitmap, as simple as that. From the beginning, the first step was to create a basic desktop app

Since the app Visual Studio creates does not include a Window class definition, I declared the bitmap as a global variable

// Global Variables:
HINSTANCE hInst;                                // current instance
WCHAR szTitle[MAX_LOADSTRING];                  // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING];            // the main window class name


// -- edit
Bitmap* bmap;

even though current GDI documentation says Bitmap is declared in gdiplusheaders.h, if I place

#include <gdiplusheaders.h>

it will show a lot of errors. What finally worked by copying from an example was

#include "framework.h"
#include "WindowsProject1.h"

// -- edit
#include <windows.h>
#include <objidl.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib,"Gdiplus.lib")

To initialize the bitmap, in the mWinMain function, before the message loop I placed this:

 // -- edit
 try {
     bmap = new Bitmap(L"test.png");
     //if (bmap->)
 }
 catch (int _exc) {
     return FALSE;
 }

I could not find any information on how to check if the bitmap was loaded correctly or not. The constructor does not throw an exception, and there was no difference whether I copied test.png in the source folder or not. I also could not find a property or a flag showing if the bitmap was able to load correctly in the bitmap object

I copied some lines from the GetPixel example, that is supposed to change pixels in a checker pattern, I was not able to see the patter either, so the bitmap may not render at all

To paint the bitmap, in the paint event I placed this:

case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hWnd, &ps);
        
        // TODO: Add any drawing code that uses hdc here...

        Graphics _gr(hWnd);
        _gr.DrawImage(bmap, 0, 0);


        EndPaint(hWnd, &ps);
    }
    break;

That's all. If there is a test.png file in the same folder as the program is supposed to create a bitmap from that file and render it, nothing complicated, but is not doing it. The window does not show any bitmap. I placed the file both in the same source folder and in the binary output folder, I tried to run it both ways and it does not show any bitmap. Any pointers?

Thanks

Windows API - Win32
Windows API - Win32
A core set of Windows application programming interfaces (APIs) for desktop and server applications. Previously known as Win32 API.
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Accepted answer
  1. RLWA32 45,396 Reputation points
    2024-10-02T06:27:47.6666667+00:00
    1 person found this answer helpful.
    0 comments

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  1. Castorix31 84,956 Reputation points
    2024-10-02T06:38:15.85+00:00

    You must initialize GdiPlus and you can test GetLastStatus

    Basic sample :

    #include <windows.h>
#include <tchar.h>

#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment(lib, "gdiplus.lib")

#pragma comment(linker,"\"/manifestdependency:type='win32' \
name='Microsoft.Windows.Common-Controls' version='6.0.0.0' \
processorArchitecture='*' publicKeyToken='6595b64144ccf1df' language='*'\"")

HINSTANCE hInst;
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int nWidth = 600, nHeight = 400;
Gdiplus::Bitmap* bitmap = NULL;

int APIENTRY wWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ LPWSTR lpCmdLine, _In_ int nCmdShow)
{
	 GdiplusStartupInput gdiplusStartupInput;
	 ULONG_PTR gdiplusToken;
	 GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

	hInst = hInstance;
	WNDCLASSEX wcex =
	{
		sizeof(WNDCLASSEX), CS_HREDRAW | CS_VREDRAW, WndProc, 0, 0, hInst, LoadIcon(NULL, IDI_APPLICATION),
		LoadCursor(NULL, IDC_ARROW), (HBRUSH)(COLOR_WINDOW + 1), NULL, TEXT("WindowClass"), NULL,
	};
	if (!RegisterClassEx(&wcex))
		return MessageBox(NULL, TEXT("Cannot register class !"), TEXT("Error"), MB_ICONERROR | MB_OK);
	int nX = (GetSystemMetrics(SM_CXSCREEN) - nWidth) / 2, nY = (GetSystemMetrics(SM_CYSCREEN) - nHeight) / 2;
	HWND hWnd = CreateWindowEx(0, wcex.lpszClassName, TEXT("Test"), WS_OVERLAPPEDWINDOW, nX, nY, nWidth, nHeight, NULL, NULL, hInst, NULL);
	if (!hWnd)
		return MessageBox(NULL, TEXT("Cannot create window !"), TEXT("Error"), MB_ICONERROR | MB_OK);
	ShowWindow(hWnd, SW_SHOWNORMAL);
	UpdateWindow(hWnd);
	MSG msg;
	while (GetMessage(&msg, NULL, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}
	GdiplusShutdown(gdiplusToken);
	return (int)msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	static HWND hWndButton = NULL, hWndStatic = NULL;
	int wmId, wmEvent;
	switch (message)
	{
	case WM_CREATE:
	{
		bitmap = new Gdiplus::Bitmap(L"Hulk.png");
		if (bitmap->GetLastStatus() != Ok)
		{
			delete bitmap;
			bitmap = NULL;
		}
		return 0;
	}
	break;
	case WM_PAINT:
	{
		PAINTSTRUCT ps;
		HDC hDC = BeginPaint(hWnd, &ps);
		if (bitmap != NULL)
		{			
			Graphics graphics(hDC);
			graphics.DrawImage(bitmap, 0, 0);
		}
		EndPaint(hWnd, &ps);
	}
	break;
	case WM_DESTROY:
	{
		if (bitmap != NULL)
		{
			delete bitmap;
			bitmap = NULL;
		}
		PostQuitMessage(0);
		return 0;
	}
	break;
	default:
		return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return 0;
}
    1 person found this answer helpful.
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  2. VooDooChicken 40 Reputation points
    2024-10-03T03:12:48.74+00:00

    thank you both, it seems it had to do with not initializing GDI.

    Initially I changed my wWinMain (for default app created by wizard) for this, it still did not work not sure why:

    int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
    _In_opt_ HINSTANCE hPrevInstance,
    _In_ LPWSTR    lpCmdLine,
    _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // TODO: Place code here.

    // Initialize global strings
    LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadStringW(hInstance, IDC_WINDOWSPROJECT1, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

    // Perform application initialization:
    if (!InitInstance(hInstance, nCmdShow))
    {
        return FALSE;
    }

    // -- edit
    try {
        if (GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL) != Ok)
            return FALSE;
        bmap = new Bitmap(L"test.png");         //if (bmap->)
    }
    catch (int _exc) {
        return FALSE;
    }

    HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WINDOWSPROJECT1));

    MSG msg;

    // Main message loop:
    while (GetMessage(&msg, nullptr, 0, 0))
    {
        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    // -- edit
    GdiplusShutdown(gdiplusToken);

    return (int)msg.wParam;
}

    but then I copied/pasted the example that shows how to start GDI in desktop app, I commented the first line which was giving error and did not add any value

    //#include <stdafx.h>

    and I edited the on paint handler (is ugly but is a test, is not supposed to look pretty)

    VOID OnPaint(HDC hdc)
{
    Graphics graphics(hdc);
    Pen      pen(Color(255, 0, 0, 255));
    graphics.DrawLine(&pen, 0, 0, 200, 100);
    // --
    Bitmap* bmap;
    bmap = new Bitmap(L"test.png");
    graphics.DrawImage(bmap, 0, 0);
}

    and now it works, it does show the bitmap. Thank you

  3. Tong Xu - MSFT 2,456 Reputation points Microsoft Vendor
    2024-10-03T03:17:12.8333333+00:00

    You are missing a call to GdiplusStartup. It is necessary.

    GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    No need to be so complicated. Image::FromFile from gdiplus will be easier. https://stackoverflow.com/questions/78143741/winapi-32-and-gdi-move-window-when-draggin-a-png-image-with-some-region-with-tr

    Image* image; // Declare the image pointer globally
int imageWidth = 0;
int imageHeight = 0;
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    // Initialize GDI+
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    // Load the PNG image
    image = Image::FromFile(L"C:\\Users\\hacktooth\\Downloads\\bg.png"); // Replace with your image path
    if (image) {
        imageWidth = image->GetWidth();
        imageHeight = image->GetHeight();
...
...
    }
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