屏幕截图 WinAPI - 可用内存
Screenshot WinAPI - Free Memory
一两天前我已经问过一个非常相似的问题，但我的问题不是很清楚，所以我尝试在这里重新表述：
我想截取屏幕截图，为此我搜索并找到了这段代码：
#include <windows.h>
#include <stdio.h>
inline int GetFilePointer(HANDLE FileHandle)
{
return SetFilePointer(FileHandle, 0, 0, FILE_CURRENT);
}
extern _Bool SaveBMPFile(char* filePath, HBITMAP bitmap, HDC bitmapDC, int width, int height)
{
_Bool Success = 0;
HDC SurfDC = NULL; // GDI-compatible device context for the surface
HBITMAP OffscrBmp = NULL; // bitmap that is converted to a DIB
HDC OffscrDC = NULL; // offscreen DC that we can select OffscrBmp into
LPBITMAPINFO lpbi = NULL; // bitmap format info; used by GetDIBits
LPVOID lpvBits = NULL; // pointer to bitmap bits array
HANDLE BmpFile = INVALID_HANDLE_VALUE; // destination .bmp file
BITMAPFILEHEADER bmfh; // .bmp file header
// We need an HBITMAP to convert it to a DIB:
if ((OffscrBmp = CreateCompatibleBitmap(bitmapDC, width, height)) == NULL)
return 0;
// The bitmap is empty, so let's copy the contents of the surface to it.
// For that we need to select it into a device context. We create one.
if ((OffscrDC = CreateCompatibleDC(bitmapDC)) == NULL)
return 0;
// Select OffscrBmp into OffscrDC:
HBITMAP OldBmp = (HBITMAP)SelectObject(OffscrDC, OffscrBmp);
// Now we can copy the contents of the surface to the offscreen bitmap:
BitBlt(OffscrDC, 0, 0, width, height, bitmapDC, 0, 0, SRCCOPY);
// GetDIBits requires format info about the bitmap. We can have GetDIBits
// fill a structure with that info if we pass a NULL pointer for lpvBits:
// Reserve memory for bitmap info (BITMAPINFOHEADER + largest possible
// palette):
if ((lpbi = (LPBITMAPINFO)malloc(sizeof(BITMAPINFOHEADER) + 256 * sizeof(RGBQUAD))) == NULL)
return 0;
ZeroMemory(&lpbi->bmiHeader, sizeof(BITMAPINFOHEADER));
lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
// Get info but first de-select OffscrBmp because GetDIBits requires it:
SelectObject(OffscrDC, OldBmp);
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, NULL, lpbi, DIB_RGB_COLORS))
return 0;
// Reserve memory for bitmap bits:
if ((lpvBits = malloc(lpbi->bmiHeader.biSizeImage)) == NULL)
return 0;
// Have GetDIBits convert OffscrBmp to a DIB (device-independent bitmap):
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, lpvBits, lpbi, DIB_RGB_COLORS))
return 0;
//ANSI->Unicode
LPCSTR szAnsi = filePath;
int Size = MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, NULL, 0);
LPWSTR filename = malloc(sizeof(LPWSTR) * Size);
MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, filename, Size);
// Create a file to save the DIB to:
if ((BmpFile = CreateFile(filename,
GENERIC_WRITE,
0, NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
NULL)) == INVALID_HANDLE_VALUE)
return 0;
DWORD Written; // number of bytes written by WriteFile
// Write a file header to the file:
bmfh.bfType = 19778; // 'BM'
// bmfh.bfSize = ??? // we'll write that later
bmfh.bfReserved1 = bmfh.bfReserved2 = 0;
// bmfh.bfOffBits = ??? // we'll write that later
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
// Write BITMAPINFOHEADER to the file:
if (!WriteFile(BmpFile, &lpbi->bmiHeader, sizeof(BITMAPINFOHEADER), &Written, NULL))
return 0;
if (Written < sizeof(BITMAPINFOHEADER))
return 0;
// Calculate size of palette:
int PalEntries;
// 16-bit or 32-bit bitmaps require bit masks:
if (lpbi->bmiHeader.biCompression == BI_BITFIELDS)
PalEntries = 3;
else
// bitmap is palettized?
PalEntries = (lpbi->bmiHeader.biBitCount <= 8) ?
// 2^biBitCount palette entries max.:
(int)(1 << lpbi->bmiHeader.biBitCount)
// bitmap is TrueColor -> no palette:
: 0;
// If biClrUsed use only biClrUsed palette entries:
if (lpbi->bmiHeader.biClrUsed)
PalEntries = lpbi->bmiHeader.biClrUsed;
// Write palette to the file:
if (PalEntries) {
if (!WriteFile(BmpFile, &lpbi->bmiColors, PalEntries * sizeof(RGBQUAD), &Written, NULL))
return 0;
if (Written < PalEntries * sizeof(RGBQUAD))
return 0;
}
// The current position in the file (at the beginning of the bitmap bits)
// will be saved to the BITMAPFILEHEADER:
bmfh.bfOffBits = GetFilePointer(BmpFile);
// Write bitmap bits to the file:
if (!WriteFile(BmpFile, lpvBits, lpbi->bmiHeader.biSizeImage, &Written, NULL))
return 0;
if (Written < lpbi->bmiHeader.biSizeImage)
return 0;
// The current pos. in the file is the final file size and will be saved:
bmfh.bfSize = GetFilePointer(BmpFile);
// We have all the info for the file header. Save the updated version:
SetFilePointer(BmpFile, 0, 0, FILE_BEGIN);
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
return 1;
}
_Bool ScreenCapture(char* filePath, int xStart, int yStart, int width, int height)
{
// get a DC compat. w/ the screen
HDC hDc = CreateCompatibleDC(0);
// make a bmp in memory to store the capture in
HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
// join em up
SelectObject(hDc, hBmp);
// copy from the screen to my bitmap
BitBlt(hDc, 0, 0, width, height, GetDC(0), xStart, yStart, SRCCOPY);
// save my bitmap
_Bool ret = SaveBMPFile(filePath, hBmp, hDc, width, height);
// free the bitmap memory
DeleteObject(hBmp);
return ret;
}
main()
{
ScreenCapture("screenshot.bmp", 0, 0, 1920, 1080);
FILE* Screen = NULL;
Screen = fopen("screenshot.bmp", "r"); //Error, the image is "used" somewhere...
return 0;
}
我对 WinAPI 一个字都不知道，但我在 Viual Studio 中看到每次调用 ScreenCapture() 时，都会有未释放的 RAM，这是个问题。
如果你们中的一些人知道错误在哪里...
感谢帮助，谢谢 :)
这是最终代码，运行没有问题，没有内存泄漏：
#include <windows.h>
#include <stdio.h>
// Helper function to retrieve current position of file pointer:
inline int GetFilePointer(HANDLE FileHandle)
{
return SetFilePointer(FileHandle, 0, 0, FILE_CURRENT);
}
//---------------------------------------------------------------------------
// Screenshot
// -> FileName: Name of file to save screenshot to
// -> lpDDS: DirectDraw surface to capture
// <- Result: Success
//
extern _Bool SaveBMPFile(char* filePath, HBITMAP bitmap, HDC bitmapDC, int width, int height)
{
_Bool Success = 0;
HBITMAP OffscrBmp = NULL; // bitmap that is converted to a DIB
HDC OffscrDC = NULL; // offscreen DC that we can select OffscrBmp into
LPBITMAPINFO lpbi = NULL; // bitmap format info; used by GetDIBits
LPVOID lpvBits = NULL; // pointer to bitmap bits array
HANDLE BmpFile = INVALID_HANDLE_VALUE; // destination .bmp file
BITMAPFILEHEADER bmfh; // .bmp file header
// We need an HBITMAP to convert it to a DIB:
if ((OffscrBmp = CreateCompatibleBitmap(bitmapDC, width, height)) == NULL)
return 0;
// The bitmap is empty, so let's copy the contents of the surface to it.
// For that we need to select it into a device context. We create one.
if ((OffscrDC = CreateCompatibleDC(bitmapDC)) == NULL)
return 0;
// Select OffscrBmp into OffscrDC:
HBITMAP OldBmp = (HBITMAP)SelectObject(OffscrDC, OffscrBmp);
// Now we can copy the contents of the surface to the offscreen bitmap:
BitBlt(OffscrDC, 0, 0, width, height, bitmapDC, 0, 0, SRCCOPY);
// GetDIBits requires format info about the bitmap. We can have GetDIBits
// fill a structure with that info if we pass a NULL pointer for lpvBits:
// Reserve memory for bitmap info (BITMAPINFOHEADER + largest possible
// palette):
if ((lpbi = (LPBITMAPINFO)malloc(sizeof(BITMAPINFOHEADER) + 256 * sizeof(RGBQUAD))) == NULL)
return 0;
ZeroMemory(&lpbi->bmiHeader, sizeof(BITMAPINFOHEADER));
lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
// Get info but first de-select OffscrBmp because GetDIBits requires it:
SelectObject(OffscrDC, OldBmp);
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, NULL, lpbi, DIB_RGB_COLORS))
return 0;
// Reserve memory for bitmap bits:
if ((lpvBits = malloc(lpbi->bmiHeader.biSizeImage)) == NULL)
return 0;
// Have GetDIBits convert OffscrBmp to a DIB (device-independent bitmap):
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, lpvBits, lpbi, DIB_RGB_COLORS))
return 0;
//ANSI->Unicode
LPCSTR szAnsi = filePath;
int Size = MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, NULL, 0);
LPWSTR filename = malloc(sizeof(LPWSTR) * Size);
MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, filename, Size);
// Create a file to save the DIB to:
if ((BmpFile = CreateFile(filename,
GENERIC_WRITE,
0, NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
NULL)) == INVALID_HANDLE_VALUE)
return 0;
DWORD Written; // number of bytes written by WriteFile
// Write a file header to the file:
bmfh.bfType = 19778; // 'BM'
// bmfh.bfSize = ??? // we'll write that later
bmfh.bfReserved1 = bmfh.bfReserved2 = 0;
// bmfh.bfOffBits = ??? // we'll write that later
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
// Write BITMAPINFOHEADER to the file:
if (!WriteFile(BmpFile, &lpbi->bmiHeader, sizeof(BITMAPINFOHEADER), &Written, NULL))
return 0;
if (Written < sizeof(BITMAPINFOHEADER))
return 0;
// Calculate size of palette:
int PalEntries;
// 16-bit or 32-bit bitmaps require bit masks:
if (lpbi->bmiHeader.biCompression == BI_BITFIELDS)
PalEntries = 3;
else
// bitmap is palettized?
PalEntries = (lpbi->bmiHeader.biBitCount <= 8) ?
// 2^biBitCount palette entries max.:
(int)(1 << lpbi->bmiHeader.biBitCount)
// bitmap is TrueColor -> no palette:
: 0;
// If biClrUsed use only biClrUsed palette entries:
if (lpbi->bmiHeader.biClrUsed)
PalEntries = lpbi->bmiHeader.biClrUsed;
// Write palette to the file:
if (PalEntries) {
if (!WriteFile(BmpFile, &lpbi->bmiColors, PalEntries * sizeof(RGBQUAD), &Written, NULL))
return 0;
if (Written < PalEntries * sizeof(RGBQUAD))
return 0;
}
// The current position in the file (at the beginning of the bitmap bits)
// will be saved to the BITMAPFILEHEADER:
bmfh.bfOffBits = GetFilePointer(BmpFile);
// Write bitmap bits to the file:
if (!WriteFile(BmpFile, lpvBits, lpbi->bmiHeader.biSizeImage, &Written, NULL))
return 0;
if (Written < lpbi->bmiHeader.biSizeImage)
return 0;
// The current pos. in the file is the final file size and will be saved:
bmfh.bfSize = GetFilePointer(BmpFile);
// We have all the info for the file header. Save the updated version:
SetFilePointer(BmpFile, 0, 0, FILE_BEGIN);
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
DeleteObject(OffscrBmp);
DeleteObject(OldBmp);
DeleteDC(OffscrDC);
CloseHandle(BmpFile);
free(lpbi);
free(lpvBits);
free(filename);
return 1;
}
_Bool ScreenCapture(char* filePath, int xStart, int yStart, int width, int height)
{
// get a DC compat. w/ the screen
HDC hDc = CreateCompatibleDC(0);
// make a bmp in memory to store the capture in
HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
// join em up
SelectObject(hDc, hBmp);
// copy from the screen to my bitmap
BitBlt(hDc, 0, 0, width, height, GetDC(0), xStart, yStart, SRCCOPY);
// save my bitmap
_Bool ret = SaveBMPFile(filePath, hBmp, hDc, width, height);
// free the bitmap memory
DeleteObject(hBmp);
DeleteDC(hDc);
return ret;
}
main()
{
ScreenCapture("screenshot.png", 0, 0, 1920, 1080);
return 0;
}
HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
GetDC(0) 必须用 ReleasedDC 清理。那样写GetDC(0)的时候，是无法清理的。您的程序只有 10,000 个可用的 GDI 句柄，因此这种资源泄漏可能是一个严重的问题。
你应该这样做：
HDC hdc_desktop = GetDC(HWND_DESKTOP);
HBITMAP hBmp = CreateCompatibleBitmap(hdc_desktop, width, height);
...
ReleaseDC(HWND_DESKTOP, hdc_desktop);
HWND_DESKTOP 就是 0，为了清楚起见，我使用了它。 GetDC returns 句柄hdc_desktop 最后可以清理
DeleteObject(hBmp)是一个小bug，因为hBmp目前在hDc中选中，无法删除。很多程序员都犯了这个错误，所以更新的 Windows 版本（我认为从 XP 开始）已经开始期待这个，所以 Windows 修复了这个错误（至少在这种情况下）但是你真的应该保存一个处理旧位图，恢复旧位图，然后删除新位图。
GetDIBits 还有一个小错误。文档说调用函数时不得在 dc 中选择 hbitmap。但是再次 Windows 习惯于看到这个错误并修复它。
你的SaveBMPFile可以简化。您不是在保存调色板位图，您可以完全忽略调色板。
未解决的问题：您使用的是 Unicode 函数，因此您使用 UTF-16 字符串文字：L"screenshot.bmp" 而不是 "screenshot.bmp"
extern _Bool SaveBMPFile(const wchar_t* filePath,
HDC memdc, HBITMAP hbitmap, int width, int height)
{
_Bool success = 0;
WORD bpp = 24; //or 32 for 32-bit bitmap
DWORD size = ((width * bpp + 31) / 32) * 4 * height;
BITMAPFILEHEADER filehdr = { 0 };
filehdr.bfType = 19778;
filehdr.bfSize = 54 + size;
filehdr.bfOffBits = 54;
//54 = 14 + 40, sizeof BITMAPFILEHEADER & BITMAPINFOHEADER
BITMAPINFOHEADER infohdr = { sizeof(infohdr) };
infohdr.biWidth = width;
infohdr.biHeight = height;
infohdr.biPlanes = 1;
infohdr.biBitCount = bpp;
BYTE *bits = malloc(size);
GetDIBits(memdc, hbitmap, 0, height, bits, (BITMAPINFO*)&infohdr, DIB_RGB_COLORS);
HANDLE hfile = CreateFileW(filePath,
GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if(hfile != INVALID_HANDLE_VALUE)
{
DWORD temp;
WriteFile(hfile, &filehdr, 14, &temp, NULL);
WriteFile(hfile, &infohdr, 40, &temp, NULL);
WriteFile(hfile, bits, size, &temp, NULL);
CloseHandle(hfile);
success = 1;
}
free(bits);
return success;
}
_Bool ScreenCapture(const wchar_t* filePath, int x, int y, int width, int height)
{
HDC hdc = GetDC(HWND_DESKTOP);
HDC memdc = CreateCompatibleDC(hdc);
HBITMAP hbitmap = CreateCompatibleBitmap(hdc, width, height);
HBITMAP oldbitmap = SelectObject(memdc, hbitmap);
BitBlt(memdc, 0, 0, width, height, hdc, x, y, SRCCOPY);
SelectObject(memdc, oldbitmap);
_Bool ret = SaveBMPFile(filePath, memdc, hbitmap, width, height);
DeleteObject(hbitmap);
DeleteDC(memdc);
ReleaseDC(HWND_DESKTOP, hdc);
return ret;
}
int main(void)
{
ScreenCapture(L"screenshot.bmp", 0, 0,
GetSystemMetrics(SM_CXFULLSCREEN), GetSystemMetrics(SM_CYFULLSCREEN));
return 0;
}
您可以运行循环执行此操作并在 Taskman 中观察 GDI 句柄以确保没有泄漏。
一两天前我已经问过一个非常相似的问题，但我的问题不是很清楚，所以我尝试在这里重新表述：
我想截取屏幕截图，为此我搜索并找到了这段代码：
#include <windows.h>
#include <stdio.h>
inline int GetFilePointer(HANDLE FileHandle)
{
return SetFilePointer(FileHandle, 0, 0, FILE_CURRENT);
}
extern _Bool SaveBMPFile(char* filePath, HBITMAP bitmap, HDC bitmapDC, int width, int height)
{
_Bool Success = 0;
HDC SurfDC = NULL; // GDI-compatible device context for the surface
HBITMAP OffscrBmp = NULL; // bitmap that is converted to a DIB
HDC OffscrDC = NULL; // offscreen DC that we can select OffscrBmp into
LPBITMAPINFO lpbi = NULL; // bitmap format info; used by GetDIBits
LPVOID lpvBits = NULL; // pointer to bitmap bits array
HANDLE BmpFile = INVALID_HANDLE_VALUE; // destination .bmp file
BITMAPFILEHEADER bmfh; // .bmp file header
// We need an HBITMAP to convert it to a DIB:
if ((OffscrBmp = CreateCompatibleBitmap(bitmapDC, width, height)) == NULL)
return 0;
// The bitmap is empty, so let's copy the contents of the surface to it.
// For that we need to select it into a device context. We create one.
if ((OffscrDC = CreateCompatibleDC(bitmapDC)) == NULL)
return 0;
// Select OffscrBmp into OffscrDC:
HBITMAP OldBmp = (HBITMAP)SelectObject(OffscrDC, OffscrBmp);
// Now we can copy the contents of the surface to the offscreen bitmap:
BitBlt(OffscrDC, 0, 0, width, height, bitmapDC, 0, 0, SRCCOPY);
// GetDIBits requires format info about the bitmap. We can have GetDIBits
// fill a structure with that info if we pass a NULL pointer for lpvBits:
// Reserve memory for bitmap info (BITMAPINFOHEADER + largest possible
// palette):
if ((lpbi = (LPBITMAPINFO)malloc(sizeof(BITMAPINFOHEADER) + 256 * sizeof(RGBQUAD))) == NULL)
return 0;
ZeroMemory(&lpbi->bmiHeader, sizeof(BITMAPINFOHEADER));
lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
// Get info but first de-select OffscrBmp because GetDIBits requires it:
SelectObject(OffscrDC, OldBmp);
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, NULL, lpbi, DIB_RGB_COLORS))
return 0;
// Reserve memory for bitmap bits:
if ((lpvBits = malloc(lpbi->bmiHeader.biSizeImage)) == NULL)
return 0;
// Have GetDIBits convert OffscrBmp to a DIB (device-independent bitmap):
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, lpvBits, lpbi, DIB_RGB_COLORS))
return 0;
//ANSI->Unicode
LPCSTR szAnsi = filePath;
int Size = MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, NULL, 0);
LPWSTR filename = malloc(sizeof(LPWSTR) * Size);
MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, filename, Size);
// Create a file to save the DIB to:
if ((BmpFile = CreateFile(filename,
GENERIC_WRITE,
0, NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
NULL)) == INVALID_HANDLE_VALUE)
return 0;
DWORD Written; // number of bytes written by WriteFile
// Write a file header to the file:
bmfh.bfType = 19778; // 'BM'
// bmfh.bfSize = ??? // we'll write that later
bmfh.bfReserved1 = bmfh.bfReserved2 = 0;
// bmfh.bfOffBits = ??? // we'll write that later
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
// Write BITMAPINFOHEADER to the file:
if (!WriteFile(BmpFile, &lpbi->bmiHeader, sizeof(BITMAPINFOHEADER), &Written, NULL))
return 0;
if (Written < sizeof(BITMAPINFOHEADER))
return 0;
// Calculate size of palette:
int PalEntries;
// 16-bit or 32-bit bitmaps require bit masks:
if (lpbi->bmiHeader.biCompression == BI_BITFIELDS)
PalEntries = 3;
else
// bitmap is palettized?
PalEntries = (lpbi->bmiHeader.biBitCount <= 8) ?
// 2^biBitCount palette entries max.:
(int)(1 << lpbi->bmiHeader.biBitCount)
// bitmap is TrueColor -> no palette:
: 0;
// If biClrUsed use only biClrUsed palette entries:
if (lpbi->bmiHeader.biClrUsed)
PalEntries = lpbi->bmiHeader.biClrUsed;
// Write palette to the file:
if (PalEntries) {
if (!WriteFile(BmpFile, &lpbi->bmiColors, PalEntries * sizeof(RGBQUAD), &Written, NULL))
return 0;
if (Written < PalEntries * sizeof(RGBQUAD))
return 0;
}
// The current position in the file (at the beginning of the bitmap bits)
// will be saved to the BITMAPFILEHEADER:
bmfh.bfOffBits = GetFilePointer(BmpFile);
// Write bitmap bits to the file:
if (!WriteFile(BmpFile, lpvBits, lpbi->bmiHeader.biSizeImage, &Written, NULL))
return 0;
if (Written < lpbi->bmiHeader.biSizeImage)
return 0;
// The current pos. in the file is the final file size and will be saved:
bmfh.bfSize = GetFilePointer(BmpFile);
// We have all the info for the file header. Save the updated version:
SetFilePointer(BmpFile, 0, 0, FILE_BEGIN);
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
return 1;
}
_Bool ScreenCapture(char* filePath, int xStart, int yStart, int width, int height)
{
// get a DC compat. w/ the screen
HDC hDc = CreateCompatibleDC(0);
// make a bmp in memory to store the capture in
HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
// join em up
SelectObject(hDc, hBmp);
// copy from the screen to my bitmap
BitBlt(hDc, 0, 0, width, height, GetDC(0), xStart, yStart, SRCCOPY);
// save my bitmap
_Bool ret = SaveBMPFile(filePath, hBmp, hDc, width, height);
// free the bitmap memory
DeleteObject(hBmp);
return ret;
}
main()
{
ScreenCapture("screenshot.bmp", 0, 0, 1920, 1080);
FILE* Screen = NULL;
Screen = fopen("screenshot.bmp", "r"); //Error, the image is "used" somewhere...
return 0;
}
我对 WinAPI 一个字都不知道，但我在 Viual Studio 中看到每次调用 ScreenCapture() 时，都会有未释放的 RAM，这是个问题。
如果你们中的一些人知道错误在哪里...
感谢帮助，谢谢 :)
这是最终代码，运行没有问题，没有内存泄漏：
#include <windows.h>
#include <stdio.h>
// Helper function to retrieve current position of file pointer:
inline int GetFilePointer(HANDLE FileHandle)
{
return SetFilePointer(FileHandle, 0, 0, FILE_CURRENT);
}
//---------------------------------------------------------------------------
// Screenshot
// -> FileName: Name of file to save screenshot to
// -> lpDDS: DirectDraw surface to capture
// <- Result: Success
//
extern _Bool SaveBMPFile(char* filePath, HBITMAP bitmap, HDC bitmapDC, int width, int height)
{
_Bool Success = 0;
HBITMAP OffscrBmp = NULL; // bitmap that is converted to a DIB
HDC OffscrDC = NULL; // offscreen DC that we can select OffscrBmp into
LPBITMAPINFO lpbi = NULL; // bitmap format info; used by GetDIBits
LPVOID lpvBits = NULL; // pointer to bitmap bits array
HANDLE BmpFile = INVALID_HANDLE_VALUE; // destination .bmp file
BITMAPFILEHEADER bmfh; // .bmp file header
// We need an HBITMAP to convert it to a DIB:
if ((OffscrBmp = CreateCompatibleBitmap(bitmapDC, width, height)) == NULL)
return 0;
// The bitmap is empty, so let's copy the contents of the surface to it.
// For that we need to select it into a device context. We create one.
if ((OffscrDC = CreateCompatibleDC(bitmapDC)) == NULL)
return 0;
// Select OffscrBmp into OffscrDC:
HBITMAP OldBmp = (HBITMAP)SelectObject(OffscrDC, OffscrBmp);
// Now we can copy the contents of the surface to the offscreen bitmap:
BitBlt(OffscrDC, 0, 0, width, height, bitmapDC, 0, 0, SRCCOPY);
// GetDIBits requires format info about the bitmap. We can have GetDIBits
// fill a structure with that info if we pass a NULL pointer for lpvBits:
// Reserve memory for bitmap info (BITMAPINFOHEADER + largest possible
// palette):
if ((lpbi = (LPBITMAPINFO)malloc(sizeof(BITMAPINFOHEADER) + 256 * sizeof(RGBQUAD))) == NULL)
return 0;
ZeroMemory(&lpbi->bmiHeader, sizeof(BITMAPINFOHEADER));
lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
// Get info but first de-select OffscrBmp because GetDIBits requires it:
SelectObject(OffscrDC, OldBmp);
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, NULL, lpbi, DIB_RGB_COLORS))
return 0;
// Reserve memory for bitmap bits:
if ((lpvBits = malloc(lpbi->bmiHeader.biSizeImage)) == NULL)
return 0;
// Have GetDIBits convert OffscrBmp to a DIB (device-independent bitmap):
if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, lpvBits, lpbi, DIB_RGB_COLORS))
return 0;
//ANSI->Unicode
LPCSTR szAnsi = filePath;
int Size = MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, NULL, 0);
LPWSTR filename = malloc(sizeof(LPWSTR) * Size);
MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, filename, Size);
// Create a file to save the DIB to:
if ((BmpFile = CreateFile(filename,
GENERIC_WRITE,
0, NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
NULL)) == INVALID_HANDLE_VALUE)
return 0;
DWORD Written; // number of bytes written by WriteFile
// Write a file header to the file:
bmfh.bfType = 19778; // 'BM'
// bmfh.bfSize = ??? // we'll write that later
bmfh.bfReserved1 = bmfh.bfReserved2 = 0;
// bmfh.bfOffBits = ??? // we'll write that later
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
// Write BITMAPINFOHEADER to the file:
if (!WriteFile(BmpFile, &lpbi->bmiHeader, sizeof(BITMAPINFOHEADER), &Written, NULL))
return 0;
if (Written < sizeof(BITMAPINFOHEADER))
return 0;
// Calculate size of palette:
int PalEntries;
// 16-bit or 32-bit bitmaps require bit masks:
if (lpbi->bmiHeader.biCompression == BI_BITFIELDS)
PalEntries = 3;
else
// bitmap is palettized?
PalEntries = (lpbi->bmiHeader.biBitCount <= 8) ?
// 2^biBitCount palette entries max.:
(int)(1 << lpbi->bmiHeader.biBitCount)
// bitmap is TrueColor -> no palette:
: 0;
// If biClrUsed use only biClrUsed palette entries:
if (lpbi->bmiHeader.biClrUsed)
PalEntries = lpbi->bmiHeader.biClrUsed;
// Write palette to the file:
if (PalEntries) {
if (!WriteFile(BmpFile, &lpbi->bmiColors, PalEntries * sizeof(RGBQUAD), &Written, NULL))
return 0;
if (Written < PalEntries * sizeof(RGBQUAD))
return 0;
}
// The current position in the file (at the beginning of the bitmap bits)
// will be saved to the BITMAPFILEHEADER:
bmfh.bfOffBits = GetFilePointer(BmpFile);
// Write bitmap bits to the file:
if (!WriteFile(BmpFile, lpvBits, lpbi->bmiHeader.biSizeImage, &Written, NULL))
return 0;
if (Written < lpbi->bmiHeader.biSizeImage)
return 0;
// The current pos. in the file is the final file size and will be saved:
bmfh.bfSize = GetFilePointer(BmpFile);
// We have all the info for the file header. Save the updated version:
SetFilePointer(BmpFile, 0, 0, FILE_BEGIN);
if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
return 0;
if (Written < sizeof(bmfh))
return 0;
DeleteObject(OffscrBmp);
DeleteObject(OldBmp);
DeleteDC(OffscrDC);
CloseHandle(BmpFile);
free(lpbi);
free(lpvBits);
free(filename);
return 1;
}
_Bool ScreenCapture(char* filePath, int xStart, int yStart, int width, int height)
{
// get a DC compat. w/ the screen
HDC hDc = CreateCompatibleDC(0);
// make a bmp in memory to store the capture in
HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
// join em up
SelectObject(hDc, hBmp);
// copy from the screen to my bitmap
BitBlt(hDc, 0, 0, width, height, GetDC(0), xStart, yStart, SRCCOPY);
// save my bitmap
_Bool ret = SaveBMPFile(filePath, hBmp, hDc, width, height);
// free the bitmap memory
DeleteObject(hBmp);
DeleteDC(hDc);
return ret;
}
main()
{
ScreenCapture("screenshot.png", 0, 0, 1920, 1080);
return 0;
}
HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
GetDC(0) 必须用 ReleasedDC 清理。那样写GetDC(0)的时候，是无法清理的。您的程序只有 10,000 个可用的 GDI 句柄，因此这种资源泄漏可能是一个严重的问题。
你应该这样做：
HDC hdc_desktop = GetDC(HWND_DESKTOP);
HBITMAP hBmp = CreateCompatibleBitmap(hdc_desktop, width, height);
...
ReleaseDC(HWND_DESKTOP, hdc_desktop);
HWND_DESKTOP 就是 0，为了清楚起见，我使用了它。 GetDC returns 句柄hdc_desktop 最后可以清理
DeleteObject(hBmp)是一个小bug，因为hBmp目前在hDc中选中，无法删除。很多程序员都犯了这个错误，所以更新的 Windows 版本（我认为从 XP 开始）已经开始期待这个，所以 Windows 修复了这个错误（至少在这种情况下）但是你真的应该保存一个处理旧位图，恢复旧位图，然后删除新位图。
GetDIBits 还有一个小错误。文档说调用函数时不得在 dc 中选择 hbitmap。但是再次 Windows 习惯于看到这个错误并修复它。
你的SaveBMPFile可以简化。您不是在保存调色板位图，您可以完全忽略调色板。
未解决的问题：您使用的是 Unicode 函数，因此您使用 UTF-16 字符串文字：L"screenshot.bmp" 而不是 "screenshot.bmp"
extern _Bool SaveBMPFile(const wchar_t* filePath,
HDC memdc, HBITMAP hbitmap, int width, int height)
{
_Bool success = 0;
WORD bpp = 24; //or 32 for 32-bit bitmap
DWORD size = ((width * bpp + 31) / 32) * 4 * height;
BITMAPFILEHEADER filehdr = { 0 };
filehdr.bfType = 19778;
filehdr.bfSize = 54 + size;
filehdr.bfOffBits = 54;
//54 = 14 + 40, sizeof BITMAPFILEHEADER & BITMAPINFOHEADER
BITMAPINFOHEADER infohdr = { sizeof(infohdr) };
infohdr.biWidth = width;
infohdr.biHeight = height;
infohdr.biPlanes = 1;
infohdr.biBitCount = bpp;
BYTE *bits = malloc(size);
GetDIBits(memdc, hbitmap, 0, height, bits, (BITMAPINFO*)&infohdr, DIB_RGB_COLORS);
HANDLE hfile = CreateFileW(filePath,
GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if(hfile != INVALID_HANDLE_VALUE)
{
DWORD temp;
WriteFile(hfile, &filehdr, 14, &temp, NULL);
WriteFile(hfile, &infohdr, 40, &temp, NULL);
WriteFile(hfile, bits, size, &temp, NULL);
CloseHandle(hfile);
success = 1;
}
free(bits);
return success;
}
_Bool ScreenCapture(const wchar_t* filePath, int x, int y, int width, int height)
{
HDC hdc = GetDC(HWND_DESKTOP);
HDC memdc = CreateCompatibleDC(hdc);
HBITMAP hbitmap = CreateCompatibleBitmap(hdc, width, height);
HBITMAP oldbitmap = SelectObject(memdc, hbitmap);
BitBlt(memdc, 0, 0, width, height, hdc, x, y, SRCCOPY);
SelectObject(memdc, oldbitmap);
_Bool ret = SaveBMPFile(filePath, memdc, hbitmap, width, height);
DeleteObject(hbitmap);
DeleteDC(memdc);
ReleaseDC(HWND_DESKTOP, hdc);
return ret;
}
int main(void)
{
ScreenCapture(L"screenshot.bmp", 0, 0,
GetSystemMetrics(SM_CXFULLSCREEN), GetSystemMetrics(SM_CYFULLSCREEN));
return 0;
}
您可以运行循环执行此操作并在 Taskman 中观察 GDI 句柄以确保没有泄漏。