Creating an HBITMAP from pixel buffer then rendering

Question

I want to create an HBITMAP object from a simple unsigned char pixel buffer (3-bytes per pixel) using CreateBitmap() like this...

HBITMAP hbm = CreateBitmap(width, height, 1, 24, buffer);

That appears to work fine until I try rendering it. For now, I just wanted to keep it simple and draw a 100 by 100 black pixel square on the screen but nothing shows up.

Here is a minimal setup I made:

HBITMAP hbm = NULL;

void window_init(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {

    static unsigned char buffer[30000] = {0};
    hbm = CreateBitmap(100, 100, 1, 24, buffer);

}
void window_draw(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {

    HDC hdc = BeginPaint(hwnd, &ps);
    HDC hdcMem = CreateCompatibleDC(hdc);

    HBITMAP hbmOld = SelectObject(hdcMem, hbm);
    BitBlt(hdc, 100, 100, 100, 100, hdcMem, 0, 0, SRCCOPY);

    SelectObject(hdcMem, hbmOld);
    DeleteDC(hdcMem);

    EndPaint(hwnd, &ps);

}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    switch (msg) {

        case WM_CREATE: window_init(hwnd, msg, wParam, lParam); break;
        case WM_PAINT: window_draw(hwnd, msg, wParam, lParam); break;
        case WM_CLOSE: DestroyWindow(hwnd); break;
        case WM_DESTROY: PostQuitMessage(0); break;
        default: return DefWindowProc(hwnd, msg, wParam, lParam);

    }

    return 0;

}

Here's my entire code in case you want to copy it...

#include <windows.h>
#include <stdlib.h>
#include <stdio.h>

typedef struct {

    const char *wc_name;
    const char *title;

    unsigned int width;
    unsigned int height;

} Window;

static HBITMAP hbmp = NULL;
static PAINTSTRUCT ps;

void window_create(Window *window, const char *wc_name, const char *title, unsigned int width, unsigned int height) {

    window->wc_name = wc_name;
    window->title = title;

    window->width = width;
    window->height = height;

}
void window_init(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {

    static unsigned char buffer[30000] = {0};
    hbmp = CreateBitmap(100, 100, 1, 24, buffer);

}
void window_draw(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {

    HDC hdc = BeginPaint(hwnd, &ps);
    HDC hdcMem = CreateCompatibleDC(hdc);

    HBITMAP hbmOld = SelectObject(hdcMem, hbmp);
    BitBlt(hdc, 100, 100, 100, 100, hdcMem, 0, 0, SRCCOPY);

    SelectObject(hdcMem, hbmOld);
    DeleteDC(hdcMem);;

    EndPaint(hwnd, &ps);

}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    switch (msg) {

        case WM_CREATE: window_init(hwnd, msg, wParam, lParam); break;
        case WM_PAINT: window_draw(hwnd, msg, wParam, lParam); break;
        case WM_CLOSE: DestroyWindow(hwnd); break;
        case WM_DESTROY: PostQuitMessage(0); break;
        default: return DefWindowProc(hwnd, msg, wParam, lParam);

    }

    return 0;

}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd) {

    Window window;
    window_create(&window, "Parent Window", "My Window", 1000, 1000 / 16 * 9);

    WNDCLASSEX wc = {0};
    MSG msg = {0};
    HWND hwnd = NULL;

    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = WndProc;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1);
    wc.lpszClassName = window.wc_name;
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

    if (!RegisterClassEx(&wc)) {

        MessageBox(NULL, "Failed to register application window!", "WC Registration Error!", MB_ICONEXCLAMATION | MB_OK);
        return -1;

    }

    hwnd = CreateWindowEx(

        0, window.wc_name, window.title,
        WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
        window.width, window.height, NULL, NULL, hInstance, NULL

    );

    if (!hwnd) {

        MessageBox(NULL, "Failed to launch application window!", "HWND Creation Error!", MB_ICONEXCLAMATION | MB_OK);
        return -1;

    }

    ShowWindow(hwnd, SW_MAXIMIZE);
    UpdateWindow(hwnd);

    while (GetMessage(&msg, NULL, 0, 0) > 0) {

        TranslateMessage(&msg);
        DispatchMessage(&msg);

    }

    return msg.wParam;

}

Answer 1

CreateBitmap produces a handle to a device dependent bitmap unlike CreateDIBSection which is guaranteed to create a device-independent bitmap with the device context if it succeeds, and allows you access to the actual bits in the bitmap, unlike CreateCompatibleBitmap.

How to use CreateDIBSection:

HDC hdc = GetDC(hwnd);
BITMAPINFO bi = { 0 };
static BYTE *bits = NULL;
static unsigned char buffer[30000] = { 0 };

bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bi.bmiHeader.biWidth = 100;
bi.bmiHeader.biHeight = -100;
bi.bmiHeader.biPlanes = 1;
bi.bmiHeader.biBitCount = 24;
bi.bmiHeader.biCompression = BI_RGB;

hbmp = CreateDIBSection(hdc, &bi, DIB_RGB_COLORS, (void**)&bits, NULL, 0);
CopyMemory(bits, buffer, 30000);
ReleaseDC(hwnd, hdc);