Failed in Creating DDB Grayscale Bitmap with 24bit RGB by C++ - c++

Question

I am trying to create a DDB Grayscale Bitmap using 24BitRGB format by C++. But I always get a bitmap with black block at bottom. It will be very appreciated if someone can help me on this issue. Many thanks.
The bitmap is : 1024x408 widthxheight
Below is my code:
enter code here
#include "stdafx.h"
#include "Win32Project19.h"
#include <windows.h>
#include <wingdi.h>
#include <algorithm>
#define MAX_LOADSTRING 100
// 全局变量:
HINSTANCE hInst; // 当前实例
WCHAR szTitle[MAX_LOADSTRING]; // 标题栏文本
WCHAR szWindowClass[MAX_LOADSTRING]; // 主窗口类名
// 此代码模块中包含的函数的前向声明:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM);
int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPWSTR lpCmdLine,
_In_ int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
// TODO: 在此放置代码。
// 初始化全局字符串
LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadStringW(hInstance, IDC_WIN32PROJECT19, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance);
// 执行应用程序初始化:
if (!InitInstance (hInstance, nCmdShow))
{
return FALSE;
}
HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WIN32PROJECT19));
MSG msg;
// 主消息循环:
while (GetMessage(&msg, nullptr, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return (int) msg.wParam;
}
//
// 函数: MyRegisterClass()
//
// 目的: 注册窗口类。
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEXW wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_WIN32PROJECT19));
wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_WIN32PROJECT19);
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));
return RegisterClassExW(&wcex);
}
//
// 函数: InitInstance(HINSTANCE, int)
//
// 目的: 保存实例句柄并创建主窗口
//
// 注释:
//
// 在此函数中，我们在全局变量中保存实例句柄并
// 创建和显示主程序窗口。
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance; // 将实例句柄存储在全局变量中
HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);
if (!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
//
// 函数: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// 目的: 处理主窗口的消息。
//
// WM_COMMAND - 处理应用程序菜单
// WM_PAINT - 绘制主窗口
// WM_DESTROY - 发送退出消息并返回
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
static HBITMAP hBitmap;
HDC hdcMem, hdc;
static BYTE* lpBits = new BYTE[1024*3*408];
static BYTE* p;
static int cxClient, cyClient;
int i = 0;
int c = 0;
switch (message)
{
case WM_COMMAND:
{
int wmId = LOWORD(wParam);
// 分析菜单选择:
switch (wmId)
{
case IDM_ABOUT:
DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
}
break;
case WM_CREATE:
cxClient = LOWORD(lParam);
cyClient = HIWORD(lParam);
for (int y = 0; y < 408; y++)
{
for (int x = 0; x < 1024; x++)
{
lpBits[c + 0] = i;
lpBits[c + 1] = i;
lpBits[c + 2] = i;
c += 3;
}
i++;
if (i > 255)
i = 0;
}
break;
case WM_PAINT:
{
PAINTSTRUCT ps;
hdc = BeginPaint(hWnd, &ps);
RECT rect;
// TODO: Please add code here....
hBitmap = CreateCompatibleBitmap(hdc, 1024, 408);
SetBitmapBits(hBitmap, 1024 * 3 * 408, lpBits);
GetClientRect(hWnd, &rect);
hdcMem = CreateCompatibleDC(hdc);
SelectObject(hdcMem, hBitmap);
StretchBlt(hdc, rect.left, rect.top, rect.right, rect.bottom, hdcMem, 0, 0, 1024,
408, SRCCOPY);
DeleteDC(hdcMem);
EndPaint(hWnd, &ps);
}
break;
case WM_DESTROY:
DeleteObject(hBitmap);
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
I always get below results (always a black block in the bottom):

Answer 1

You are assuming that bitmap uses 3 bytes per pixel, but it appears that you need 4 (one for alpha channel).
I got your code to work by simply replacing all 3 with 4:
static BYTE* lpBits = new BYTE[WIDTH * 4 * HEIGHT];
...
c += 4;
...
SetBitmapBits(hBitmap, WIDTH * 4 * HEIGHT, lpBits);
Also, you create your hBitmap for each WM_PAINT message you get, but delete only once, in WM_DESTROY. That causes a resource leak, that may lead to other issues. Since hBitmap is static, you can create it like this:
if (!hBitmap) {
hBitmap = CreateCompatibleBitmap(hdc, WIDTH, HEIGHT);
SetBitmapBits(hBitmap, WIDTH * 4 * HEIGHT, lpBits);
}