c ++使用GetDIBits()读取像素

Question

我正在尝试创建一个与 windows API GetPixel() 函数等效的函数，但我想创建屏幕的位图，然后读取该缓冲区。

这就是我所得到的（主要是从谷歌搜索中复制粘贴的），当我运行它时，它只打印出 0。我想我大部分都说对了，我的问题是我不知道如何读取 BYTE 变量。

所以我的问题是，我需要做什么才能让它用我的 for 循环打印出一些随机颜色（R、G 或 B）？

#include <Windows.h>
#include <iostream>
#include <math.h>
#include <stdio.h>

using namespace std;

int main() {

    HDC hdc,hdcMem;

    hdc = GetDC(NULL);
    hdcMem = CreateCompatibleDC(hdc); 

    HBITMAP hBitmap = CreateCompatibleBitmap(hdc, 1680, 1050);

    BITMAPINFO MyBMInfo = {0};
    MyBMInfo.bmiHeader.biSize = sizeof(MyBMInfo.bmiHeader); 
    // Get the BITMAPINFO structure from the bitmap
    if(0 == GetDIBits(hdcMem, hBitmap, 0, 0, NULL, &MyBMInfo, DIB_RGB_COLORS)) {
        cout << "error" << endl;
    }

    // create the bitmap buffer
    BYTE* lpPixels = new BYTE[MyBMInfo.bmiHeader.biSizeImage];

    MyBMInfo.bmiHeader.biSize = sizeof(MyBMInfo.bmiHeader);
    MyBMInfo.bmiHeader.biBitCount = 32;  
    MyBMInfo.bmiHeader.biCompression = BI_RGB;  
    MyBMInfo.bmiHeader.biHeight = abs(MyBMInfo.bmiHeader.biHeight); 

    // get the actual bitmap buffer
    if(0 == GetDIBits(hdc, hBitmap, 0, MyBMInfo.bmiHeader.biHeight, (LPVOID)lpPixels, &MyBMInfo, DIB_RGB_COLORS)) {
        cout << "error2" << endl;
    }

    for(int i = 0; i < 100; i++) {
        cout << (int)lpPixels[i] << endl;
    }

    return 0;
}

• Windows 7的
• C::B 13.12（控制台应用程序）
• 编译器：mingw32-gcc
• 库 gdi32 链接

Answer 1

按照约定，我正在添加一个带有工作代码片段的新答案（我添加了丢失的 lpPixels 清理）。请参阅我之前的回答中的讨论以及@enhzflep 所做的讨论。

#include <Windows.h>
#include <iostream>
#include <math.h>
#include <stdio.h>
using namespace std;

HBITMAP GetScreenBmp( HDC hdc) {
    // Get screen dimensions
    int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
    int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);

    // Create compatible DC, create a compatible bitmap and copy the screen using BitBlt()
    HDC hCaptureDC  = CreateCompatibleDC(hdc);
    HBITMAP hBitmap = CreateCompatibleBitmap(hdc, nScreenWidth, nScreenHeight);
    HGDIOBJ hOld = SelectObject(hCaptureDC, hBitmap); 
    BOOL bOK = BitBlt(hCaptureDC,0,0,nScreenWidth, nScreenHeight, hdc,0,0,SRCCOPY|CAPTUREBLT); 

    SelectObject(hCaptureDC, hOld); // always select the previously selected object once done
    DeleteDC(hCaptureDC);
    return hBitmap;
}

int main() {
    HDC hdc = GetDC(0);

    HBITMAP hBitmap = GetScreenBmp(hdc);

    BITMAPINFO MyBMInfo = {0};
    MyBMInfo.bmiHeader.biSize = sizeof(MyBMInfo.bmiHeader); 

    // Get the BITMAPINFO structure from the bitmap
    if(0 == GetDIBits(hdc, hBitmap, 0, 0, NULL, &MyBMInfo, DIB_RGB_COLORS)) {
        cout << "error" << endl;
    }

    // create the bitmap buffer
    BYTE* lpPixels = new BYTE[MyBMInfo.bmiHeader.biSizeImage];

    // Better do this here - the original bitmap might have BI_BITFILEDS, which makes it
    // necessary to read the color table - you might not want this.
    MyBMInfo.bmiHeader.biCompression = BI_RGB;  

    // get the actual bitmap buffer
    if(0 == GetDIBits(hdc, hBitmap, 0, MyBMInfo.bmiHeader.biHeight, (LPVOID)lpPixels, &MyBMInfo, DIB_RGB_COLORS)) {
        cout << "error2" << endl;
    }

    for(int i = 0; i < 100; i++) {
        cout << (int)lpPixels[i];
    }

    DeleteObject(hBitmap);
    ReleaseDC(NULL, hdc);
    delete[] lpPixels;
    return 0;
}