CODEWITHSUNDEEP
c++windowsbitmapgdi
Display name
Display name

Reputation: 780

How to translate a simple bitmap in GDI

I want to be able to move an image across the screen. This is the code I have that displays the image, but it always displays the image starting at the origin.

void drawBitmap(HDC hdc, int x1, int y1, int x2, int y2, LPWSTR path) {
    HBITMAP bmp = (HBITMAP)::LoadImage(NULL, path, IMAGE_BITMAP, SCREEN_WIDTH, SCREEN_HEIGHT, LR_LOADFROMFILE);
    HGDIOBJ B1 = CreatePatternBrush(bmp);
    SelectObject(hdc, B1);
    Rectangle(hdc, x1, y1, x2, y2);
    DeleteObject(B1);
}

Thank you Barmak Shemirani for the answer. For anyone curious about what my code looks like now, I have replaced the original code with code from the guy that answered my question and it now looks like this:

HBITMAP hbitmap = (HBITMAP)LoadImage(NULL, path, IMAGE_BITMAP, x2-x1, y2-y1, LR_LOADFROMFILE);
HDC memdc = CreateCompatibleDC(hdc);
SelectObject(memdc, hbitmap);
BitBlt(hdc, x1, y1, x2, y2, memdc, 0, 0, SRCCOPY);
DeleteDC(memdc);

Upvotes: 1

Views: 193

Answers (1)

Barmak Shemirani
Barmak Shemirani

Reputation: 31599

Create a child window and override WM_NCHITTEST to return HTCAPTION, this will cause the the child window to move around main window when it is clicked.

Next, just draw the bitmap in child window

#include "windows.h"

LRESULT CALLBACK wndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
{
    if (msg == WM_DESTROY)
    {
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd, msg, wp, lp);
}

LRESULT CALLBACK bitmapProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
{
    if (msg == WM_NCHITTEST)
    {
        return HTCAPTION;
    }

    if (msg == WM_PAINT)
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        RECT rc;
        GetClientRect(hwnd, &rc);
        HBITMAP hbitmap = (HBITMAP)LoadImage(NULL, L"c:\\test\\test.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);

        HDC memdc = CreateCompatibleDC(hdc);
        HBITMAP saveOldBitmap = (HBITMAP)SelectObject(memdc, hbitmap);
        BitBlt(hdc, 0, 0, rc.right, rc.bottom, memdc, 0, 0, SRCCOPY);

        SelectObject(memdc, saveOldBitmap); //add this
        DeleteObject(hbitmap); //*** add this, important
        DeleteDC(memdc);

        EndPaint(hwnd, &ps);
    }

    return DefWindowProc(hwnd, msg, wp, lp);
}

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, LPTSTR, int)
{
    WNDCLASSEX wcex = { sizeof(WNDCLASSEX) };
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.hInstance = hInstance;
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_BTNFACE + 1);
    wcex.lpszClassName = L"mainWnd-bitmapWnd";
    wcex.lpfnWndProc = wndProc;
    if (!RegisterClassEx(&wcex))
    {
        MessageBox(0, L"error 1", 0, 0);
    }

    HWND hmain = CreateWindow(wcex.lpszClassName, L"w32", WS_CLIPCHILDREN | WS_VISIBLE | WS_OVERLAPPEDWINDOW, 0, 0, 300, 200, 0, 0, hInstance, 0);

    wcex.lpszClassName = L"bitmapWnd";
    wcex.lpfnWndProc = bitmapProc;
    if (!RegisterClassEx(&wcex))
    {
        MessageBox(0, L"error 2", 0, 0);
    }

    CreateWindow(wcex.lpszClassName, L"w32", WS_VISIBLE | WS_CHILD | WS_BORDER, 0, 0, 50, 50, hmain, 0, hInstance, 0);

    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

change the X/Y position in BitBlt to print the bitmap in a different location

Upvotes: 1

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