Winapi GetDIBits访问冲突

Question

我希望在python中获得BITMAPINFO的原始字节。这是我的完整代码：

import ctypes
from ctypes import wintypes
windll = ctypes.windll
user32 = windll.user32
gdi32 = windll.gdi32


class RECT(ctypes.Structure):
    _fields_ = [
        ('left', ctypes.c_long),
        ('top', ctypes.c_long),
        ('right', ctypes.c_long),
        ('bottom', ctypes.c_long)
    ]


class BITMAPINFOHEADER(ctypes.Structure):
    _fields_ = [
        ("biSize", wintypes.DWORD),
        ("biWidth", ctypes.c_long),
        ("biHeight", ctypes.c_long),
        ("biPlanes", wintypes.WORD),
        ("biBitCount", wintypes.WORD),
        ("biCompression", wintypes.DWORD),
        ("biSizeImage", wintypes.DWORD),
        ("biXPelsPerMeter", ctypes.c_long),
        ("biYPelsPerMeter", ctypes.c_long),
        ("biClrUsed", wintypes.DWORD),
        ("biClrImportant", wintypes.DWORD)
    ]


class RGBQUAD(ctypes.Structure):
    _fields_ = [
        ("rgbBlue", wintypes.BYTE),
        ("rgbGreen", wintypes.BYTE),
        ("rgbRed", wintypes.BYTE),
        ("rgbReserved", ctypes.c_void_p)
    ]


class BITMAP(ctypes.Structure):
    _fields_ = [
        ("bmType", ctypes.c_long),
        ("bmWidth", ctypes.c_long),
        ("bmHeight", ctypes.c_long),
        ("bmWidthBytes", ctypes.c_long),
        ("bmPlanes", wintypes.DWORD),
        ("bmBitsPixel", wintypes.DWORD),
        ("bmBits", ctypes.c_void_p)
    ]


whandle = 327756  # Just a handle of an open application
rect = RECT()
user32.GetClientRect(whandle, ctypes.byref(rect))
# bbox = (rect.left, rect.top, rect.right, rect.bottom)

hdcScreen = user32.GetDC(None)
hdc = gdi32.CreateCompatibleDC(hdcScreen)
hbmp = gdi32.CreateCompatibleBitmap(
    hdcScreen,
    rect.right - rect.left,
    rect.bottom - rect.top
)
gdi32.SelectObject(hdc, hbmp)

PW_CLIENTONLY = 1

if not user32.PrintWindow(whandle, hdc, PW_CLIENTONLY):
    raise Exception("PrintWindow failed")

bmap = BITMAP()
if not gdi32.GetObjectW(hbmp, ctypes.sizeof(BITMAP), ctypes.byref(bmap)):
    raise Exception("GetObject failed")


class BITMAPINFO(ctypes.Structure):
    _fields_ = [
        ("BITMAPINFOHEADER", BITMAPINFOHEADER),
        ("RGBQUAD", RGBQUAD * 1000)
    ]

bminfo = BITMAPINFO()
bminfo.BITMAPINFOHEADER.biSize = ctypes.sizeof(BITMAPINFOHEADER)
bminfo.BITMAPINFOHEADER.biWidth = bmap.bmWidth
bminfo.BITMAPINFOHEADER.biHeight = bmap.bmHeight
bminfo.BITMAPINFOHEADER.biPlanes = bmap.bmPlanes
bminfo.BITMAPINFOHEADER.biBitCount = bmap.bmBitsPixel
bminfo.BITMAPINFOHEADER.biCompression = 0
bminfo.BITMAPINFOHEADER.biClrImportant = 0

out = ctypes.create_string_buffer(1000)

if not gdi32.GetDIBits(hdc, hbmp, 0, bmap.bmHeight, None, bminfo, 0):
    raise Exception("GetDIBits failed")

我需要一种方法来知道RGBQUADS数组在BITMAPINFO结构中的长度以及out缓冲区的长度。1000作为占位符在那里。

访问冲突导致gdi32.GetDIBits失败。我想这是因为我必须有数组和缓冲区的正确长度。

我发了全部资料，因为我不知道是什么失败了。任何帮助都是非常感谢的。

更新

• 修正了BITMAP中的BITMAPs是WORDs，RGBQUAD中的空指针是BYTE
• 获取图像数据的大小： def round_up32(n)：multiple = 32，multiple < n: multiple += 32返回multiple data_len = round_up32(bmap.bmWidth * bmap.bmBitsPixel) * bmap.bmHeight

仍然违反了访问权限。

我也看到了那个没有用于32位/像素位图的RGBQUAD数组。。这是真的吗？

Answer 1

我所犯的错误：

• 结构(谢谢大卫)：
  • BITMAP没有DWORD；它有WORDs。
  • RGBQUAD的rgbReserved是一个BYTE，而不是一个空指针。
  • 对于每像素32位的位图，BITMAPINFO不需要RGBQUAD数组。

• 指针(谢谢罗杰，我来自python :P )：
  • GetDIBits参数lpvBits需要一个指向缓冲区的指针
  • GetDIBits参数lpbi需要指向结构的指针。

我不知道的是：

缓冲区必须有多大。引用乔纳森

位图的每一行在大小上都是bmWidth * bmBitsPixel位，舍入到下一个32位的倍数。用bmHeight乘以行长来计算图像数据的总大小。

我想出了这个：

def round_up32(n):
    multiple = 32

    while multiple < n:
        multiple += 32

    return multiple

scanline_len = round_up32(bmap.bmWidth * bmap.bmBitsPixel)
data_len = scanline_len * bmap.bmHeight

然后使用data_len对ctypes.create_string_buffer()进行无效化。

GetDIBits只返回像素数据，所以我必须构建标题。

在进行了所有这些更改后，没有什么失败的，但是图像被倒置了。我发现GetDIBits由于兼容的原因返回倒置的扫描行。我用字节做了一个新的PIL图像，然后翻转它。

全部资料来源如下：

import struct

from PIL import Image
from PIL.ImageOps import flip

import ctypes
from ctypes import wintypes
windll = ctypes.windll
user32 = windll.user32
gdi32 = windll.gdi32


class RECT(ctypes.Structure):
    _fields_ = [
        ('left', ctypes.c_long),
        ('top', ctypes.c_long),
        ('right', ctypes.c_long),
        ('bottom', ctypes.c_long)
    ]


class BITMAPINFOHEADER(ctypes.Structure):
    _fields_ = [
        ("biSize", wintypes.DWORD),
        ("biWidth", ctypes.c_long),
        ("biHeight", ctypes.c_long),
        ("biPlanes", wintypes.WORD),
        ("biBitCount", wintypes.WORD),
        ("biCompression", wintypes.DWORD),
        ("biSizeImage", wintypes.DWORD),
        ("biXPelsPerMeter", ctypes.c_long),
        ("biYPelsPerMeter", ctypes.c_long),
        ("biClrUsed", wintypes.DWORD),
        ("biClrImportant", wintypes.DWORD)
    ]


class BITMAPINFO(ctypes.Structure):
    _fields_ = [
        ("bmiHeader", BITMAPINFOHEADER)
    ]


class BITMAP(ctypes.Structure):
    _fields_ = [
        ("bmType", ctypes.c_long),
        ("bmWidth", ctypes.c_long),
        ("bmHeight", ctypes.c_long),
        ("bmWidthBytes", ctypes.c_long),
        ("bmPlanes", wintypes.WORD),
        ("bmBitsPixel", wintypes.WORD),
        ("bmBits", ctypes.c_void_p)
    ]


def get_window_image(whandle):
    def round_up32(n):
        multiple = 32

        while multiple < n:
            multiple += 32

        return multiple

    rect = RECT()
    user32.GetClientRect(whandle, ctypes.byref(rect))
    bbox = (rect.left, rect.top, rect.right, rect.bottom)

    hdcScreen = user32.GetDC(None)
    hdc = gdi32.CreateCompatibleDC(hdcScreen)
    hbmp = gdi32.CreateCompatibleBitmap(
        hdcScreen,
        bbox[2] - bbox[0],
        bbox[3] - bbox[1]
    )
    gdi32.SelectObject(hdc, hbmp)

    PW_CLIENTONLY = 1

    if not user32.PrintWindow(whandle, hdc, PW_CLIENTONLY):
        raise Exception("PrintWindow failed")

    bmap = BITMAP()
    if not gdi32.GetObjectW(hbmp, ctypes.sizeof(BITMAP), ctypes.byref(bmap)):
        raise Exception("GetObject failed")

    if bmap.bmBitsPixel != 32:
        raise Exception("WTF")

    scanline_len = round_up32(bmap.bmWidth * bmap.bmBitsPixel)
    data_len = scanline_len * bmap.bmHeight

    # http://msdn.microsoft.com/en-us/library/ms969901.aspx
    bminfo = BITMAPINFO()
    bminfo.bmiHeader.biSize = ctypes.sizeof(BITMAPINFOHEADER)
    bminfo.bmiHeader.biWidth = bmap.bmWidth
    bminfo.bmiHeader.biHeight = bmap.bmHeight
    bminfo.bmiHeader.biPlanes = 1
    bminfo.bmiHeader.biBitCount = 24  # bmap.bmBitsPixel
    bminfo.bmiHeader.biCompression = 0

    data = ctypes.create_string_buffer(data_len)

    DIB_RGB_COLORS = 0

    get_bits_success = gdi32.GetDIBits(
        hdc, hbmp,
        0, bmap.bmHeight,
        ctypes.byref(data), ctypes.byref(bminfo),
        DIB_RGB_COLORS
    )
    if not get_bits_success:
        raise Exception("GetDIBits failed")

    # http://msdn.microsoft.com/en-us/library/dd183376%28v=vs.85%29.aspx
    bmiheader_fmt = "LllHHLLllLL"

    unpacked_header = [
        bminfo.bmiHeader.biSize,
        bminfo.bmiHeader.biWidth,
        bminfo.bmiHeader.biHeight,
        bminfo.bmiHeader.biPlanes,
        bminfo.bmiHeader.biBitCount,
        bminfo.bmiHeader.biCompression,
        bminfo.bmiHeader.biSizeImage,
        bminfo.bmiHeader.biXPelsPerMeter,
        bminfo.bmiHeader.biYPelsPerMeter,
        bminfo.bmiHeader.biClrUsed,
        bminfo.bmiHeader.biClrImportant
    ]

    # Indexes: biXPelsPerMeter = 7, biYPelsPerMeter = 8
    # Value from https://stackoverflow.com/a/23982267/2065904
    unpacked_header[7] = 3779
    unpacked_header[8] = 3779

    image_header = struct.pack(bmiheader_fmt, *unpacked_header)

    image = image_header + data

    return flip(Image.frombytes("RGB", (bmap.bmWidth, bmap.bmHeight), image))

将窗口句柄(int)传递给get_window_image()，它将返回一个PIL映像。

唯一的问题是颜色是..。奇怪吗？，我改天再想办法。

Answer 2

以下代码是错误的

def round_up32(n):
    multiple = 32

    while multiple < n:
        multiple += 32

    return multiple

scanline_len = round_up32(bmap.bmWidth * bmap.bmBitsPixel)
data_len = scanline_len * bmap.bmHeight

您正在试图找到创建数组的字节数，或者只是分配一个内存块。内存总是字节。因此，bmap.bmBitsPixel应该转换为字节。32位是4字节。因为您已经在检查bmap.bmBitsPixel的32位，所以用4替换bmap.bmBitsPixel并删除round_up32函数。

scanline_len = bmap.bmWidth * 4
data_len = scanline_len * bmap.bmHeight