I want to pass image data to a C++ DLL function that looks like this:
GLFWcursor* glfwCreateCursor (
const GLFWimage* image,
int xhot,
int yhot
)
It crashes supposedly because of this struct (C#):
[StructLayout(LayoutKind.Sequential)]
public struct GlfwImage
{
public int width;
public int height;
public byte[] pixels;
}
"pixels" is of type "unsigned char *", width and height are simple int-values.
While the method can be load with that signature, I always
get a System.AccessViolationException when actually calling it.
I tried several datatypes for "pixels", including IntPtr and
actual pointers but to no effect.
Here is how I get the data and call it:
var bufferSize = texture.Size.Width * texture.Size.Height * 4;
IntPtr imageData = Marshal.AllocHGlobal(bufferSize);
GL.GetTexImage(TextureTarget.Texture2D, 0, PixelFormat.Rgba, PixelType.Bitmap, imageData);
byte[] imageChars = new byte[bufferSize];
Marshal.Copy(imageData, imageChars, 0, bufferSize);
GlfwImage cursorImage = new GlfwImage
{
pixels = imageChars,
width = texture.Size.Width,
height = texture.Size.Height
};
GlfwCursor cursor = Glfw.CreateCursor(cursorImage, texture.Size.Width / 2, texture.Size.Height / 2);
Is there something I'm overlooking?
Related
I have a trouble in transferring an image from C++ to Unity3D(C#). I used OpenCV to read a Mat type image and get the data point with img.data. When I build the dll and call the corresponding function, I get error with all data in the bytes array is 0, so I want to know how to transfer an image from C++ to C#. Thank you.
Sorry for late reply,
code shown as the follows:
C++ code:
DLL_API BYTE* _stdcall MatToByte()
{
Mat srcImg = imread("F:\\3121\\image\\image_0\\000000.png");
nHeight = srcImg.rows;
nWidth = srcImg.cols;
nBytes = nHeight * nWidth * nFlag / 8;
if (pImg)
delete[] pImg;
pImg = new BYTE[nBytes];
memcpy(pImg, srcImg.data, nBytes);
return pImg;
}
C# code
[DllImport("Display")]
public static extern IntPtr MatToByte();
byte[] Bytes = new byte[nBytes];
IntPtr tmp = MatToByte();
Marshal.Copy(tmp, Bytes, 0, nBytes);
Texture2D texture = new Texture2D(width, height);
texture.LoadImage(Bytes);
left_plane.GetComponent<Renderer>().material.mainTexture = texture;
I'm loading C++ library from my C# code dynamically. I want to find small image inside large one, converting large image to byte[] and small image read from physical path. When I call imdecode then large_img always returns 0 cols and rows.
C#
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
private delegate ImageParams GetImageParams(IntPtr dataPtr, int size, string path);
// ...
byte[] largeImgByteArr = this.BitmapToByteArray(bmp);
IntPtr dataPtr = Marshal.AllocHGlobal(largeImgByteArr.Length);
Marshal.Copy(dataPtr, largeImgByteArr, 0, largeImgByteArr.Length);
C++
ImageParams GetImageParams(BYTE* largeImgBuf, int bufLength, const char* smallImgPath)
{
Mat large_img_data(bufLength, 1, CV_32FC1, largeImgBuf);
Mat large_img = imdecode(large_img_data, IMREAD_COLOR);
Mat small_img = imread(smallImgPath, IMREAD_COLOR);
int result_cols = large_img.cols - small_img.cols + 1;
int result_rows = large_img.rows - small_img.rows + 1;
Mat result;
result.create(result_cols, result_rows, CV_32FC1);
matchTemplate(large_img, small_img, result, CV_TM_SQDIFF_NORMED);
normalize(result, result, 0, 1, NORM_MINMAX, -1, Mat());
}
What I'm doing wrong here?
Note: I have checked that image path is correct and byte array not empty.
Edit 1
I changed my code a bit by providing the large image width and height, also got rid of imdecode and changed something like in this post.
ImageParams GetImageParams(BYTE* largeImgBuf, int height, int width, int bufLength, const char* smallImgPath)
{
// Mat large_img = imdecode(large_img_data, IMREAD_COLOR);
Mat large_img = Mat(height, width, CV_8UC3, largeImgBuf);
Mat small_img = imread(templPath, 1);
/// ...
}
Now it returns rows and columns but when call matchTemplate method it throws an exception:
Remember that Bitmap structure in C# uses data padding (stride value as multiplicity of 4) whrereas OpenCV may not. Try creating Mat object directly from byte array but adjust step (stride) value as it just assigns data without any ownership or reallocation.
EDIT
Here's an example how create OpenCV Mat object from Bitmap. Data from bitmap is not copied, but only assigned. PixelFormat and OpenCV mat type must have corresponding single element size in bytes.
cv::Mat ImageBridge::cvimage(System::Drawing::Bitmap^ bitmap){
if(bitmap != nullptr){
switch(bitmap->PixelFormat){
case System::Drawing::Imaging::PixelFormat::Format24bppRgb:
return bmp2mat(bitmap, CV_8UC3);
case System::Drawing::Imaging::PixelFormat::Format8bppIndexed:
return bmp2mat(bitmap, CV_8U);
default: return cv::Mat();
}
}
else
return cv::Mat();
}
cv::Mat ImageBridge::bmp2mat(System::Drawing::Bitmap^ bitmap, int image_type){
auto bitmap_data = bitmap->LockBits(
System::Drawing::Rectangle(0, 0, bitmap->Width, bitmap->Height),
System::Drawing::Imaging::ImageLockMode::ReadWrite,
bitmap->PixelFormat);
char* bmpptr = (char*)bitmap_data->Scan0.ToPointer();
cv::Mat image(
cv::Size(bitmap->Width, bitmap->Height),
image_type,
bmpptr,
bitmap_data->Stride);
bitmap->UnlockBits(bitmap_data);
return image;
}
EDIT 2
Conversion in reverse - this time data from Mat image is copied as Bitmap allocates it's own memory.
System::Drawing::Bitmap^ ImageBridge::bitmap(cv::Mat& image){
if(!image.empty() && image.type() == CV_8UC3)
return mat2bmp(image, System::Drawing::Imaging::PixelFormat::Format24bppRgb);
else if(!image.empty() && image.type() == CV_8U)
return mat2bmp(image, System::Drawing::Imaging::PixelFormat::Format8bppIndexed);
else
return nullptr;
}
System::Drawing::Bitmap^ ImageBridge::mat2bmp(cv::Mat& image, System::Drawing::Imaging::PixelFormat pixel_format){
if(image.empty())
return nullptr;
System::Drawing::Bitmap^ bitmap = gcnew System::Drawing::Bitmap(image.cols, image.rows, pixel_format);
auto bitmap_data = bitmap->LockBits(
System::Drawing::Rectangle(0, 0, bitmap->Width, bitmap->Height),
System::Drawing::Imaging::ImageLockMode::ReadWrite,
pixel_format);
char* bmpptr = (char*)bitmap_data->Scan0.ToPointer();
int line_length = (int)image.step;
int bmp_stride = bitmap_data->Stride;
assert(!image.isSubmatrix());
assert(bmp_stride >= 0);
for(int l = 0; l < image.rows; l++){
char* cvptr = (char*)image.ptr(l);
int bmp_line_index = l * bmp_stride;
for(int i = 0; i < line_length; ++i)
bmpptr[bmp_line_index + i] = cvptr[i];
}
bitmap->UnlockBits(bitmap_data);
return bitmap;
}
Or if you have Mat image with step as multiplicity of 4 you can use non-copy version.
System::Drawing::Bitmap^ ImageBridge::bitmap2(cv::Mat& image){
System::Drawing::Bitmap^ bitmap;
assert(!image.isSubmatrix());
if(!image.empty() && image.type() == CV_8UC3){
bitmap = gcnew System::Drawing::Bitmap(
image.cols, image.rows,
3 * image.cols,
System::Drawing::Imaging::PixelFormat::Format24bppRgb,
System::IntPtr(image.data));
}
else if(!image.empty() && image.type() == CV_8U){
bitmap = gcnew System::Drawing::Bitmap(
image.cols, image.rows,
image.cols,
System::Drawing::Imaging::PixelFormat::Format8bppIndexed,
System::IntPtr(image.data));
}
return bitmap;
}
According to the documentation
The function reads an image from the specified buffer in the memory. If the buffer is too short or contains invalid data, the empty matrix/image is returned.
Try checking the error code after the imdecode part
#include <errno.h>
cout << errno;
I have a problem passing void pointer from unmanaged code to managed. There is a function's pointer in .cpp file
TESTCALLBACK_FUNCTION testCbFunc;
TESTCALLBACK_FUNCTION takes C++ structure
typedef void (*TESTCALLBACK_FUNCTION )(TImage image);
struct TImage
{
int Width; //width
int Height; //height
void *Buf; //data buffer
};
C# function and structure
public void TImageReceived(TImage image)
{
// logic
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1), Serializable]
public struct TImage
{
public int Width;
public int Height;
public IntPtr Buf;
}
TImageReceived passed to unmanaged code and when it's called I receive exception.
System.Runtime.InteropServices.SafeArrayTypeMismatchException
If I passed NULL in field Buf from unmanaged code everything will works fine.
I know about MarshalAs atrribute, but the problem is that I cannot use SizeConst because Buf size is always different. But it always has size of Width*Height.
[MarshalAs(UnmanagedType.ByValArray,SizeConst=???)]
How to cast void* from unmanaged to managed code?
Based on your comment, and assuming that TImage from your C++ code maps neatly on to your struct (Warning - if you're using TImage from the Borland VCL, then that might not map on as neatly as you're hoping)
Buf has a size Width*Height
Your best option is to use Marshal.Copy, for example
using System.Runtime.InteropServices;
/* ... */
[StructLayout(LayoutKind.Sequential)]
public struct TImage
{
public int Width;
public int Height;
public IntPtr Buf;
}
/* ... */
public void TImageReceived(TImage image)
{
var length = image.Height * image.Width;
var bytes = new byte[length];
Marshal.Copy(image.Buf, bytes, 0, length);
}
Related:
Marshalling struct with embedded pointer from C# to unmanaged driver
...However...
If TImage belongs to Borland's VCL then I would suggest re-thinking the struct, because it will involve marshalling other data inherited from TImage's base class (Borland's documentation is unclear about the class' layout) - in which case, it would be easier to pass the arguments directly:
public void TImageReceived(IntPtr buf, int width, int height)
{
var length = height * width;
var bytes = new byte[length];
Marshal.Copy(buf, bytes, 0, length);
// etc.
}
I am trying to pass a 2D mask (all 0s, expect for a region of interest as 1s) from C# ( as short[]) to C++ (as unsigned short*), but I cannot get the right value in C++.
C#
[DllImport("StatsManager.dll", EntryPoint = "SetStatsMask")]
private static extern int SetStatsMask(IntPtr mask, int imgWidth, int imgHeight);
short[] mask;
mask = new short[8*8];
// some operation here making a ROI in mask all 1. ex 0000111100000000 in 1D
IntPtr maskPtr = Marshal.AllocHGlobal(2 * mask.Length);
Marshal.Copy(mask, 0, maskPtr, mask.Length);
SetStatsMask(maskPtr, width, height);
C++
long StatsManager::SetStatsMask(unsigned short *mask, long width, long height)
{
//create memory to store the incoming mask
//memcpy the mask to the new buffer
//pMask = realloc(pMask,width*height*sizeof(unsigned short));
long ret = TRUE;
if (NULL == _pMask)
{
_pMask = new unsigned short[width * height];
}
else
{
realloc(_pMask,width*height*sizeof(unsigned short));
}
memcpy(mask,_pMask,width*height*sizeof(unsigned short));
SaveBuffer(_pMask, width, height);
return ret;
}
But all I can see for mask in C++ using watch window is 52536 instead of 0000111100000000, so I am wondering where I messed up? Anyone can help? Thanks.
I believe you misplaced the parameters of memcpy:
memcpy(mask,_pMask,width*height*sizeof(unsigned short));
As I understand you want to copy from mask to _pMask, so you should write:
memcpy(_pMask, mask, width*height*sizeof(unsigned short));
I have a byte array that needs to be displayed on the desktop (or Form). I'm using WinApi for that and not sure how to set all pixels at once. The byte array is in my memory and needs to be displayed as quickly as possible (with just WinApi).
I'm using C# but simple pseudo-code would be ok for me:
// create bitmap
byte[] bytes = ...;// contains pixel data, 1 byte per pixel
HDC desktopDC = GetWindowDC(GetDesktopWindow());
HDC bitmapDC = CreateCompatibleDC(desktopDC);
HBITMAP bitmap = CreateCompatibleBitmap(bitmapDC, 320, 240);
DeleteObject(SelectObject(bitmapDC, bitmap));
BITMAPINFO info = new BITMAPINFO();
info.bmiColors = new tagRGBQUAD[256];
for (int i = 0; i < info.bmiColors.Length; i++)
{
info.bmiColors[i].rgbRed = (byte)i;
info.bmiColors[i].rgbGreen = (byte)i;
info.bmiColors[i].rgbBlue = (byte)i;
info.bmiColors[i].rgbReserved = 0;
}
info.bmiHeader = new BITMAPINFOHEADER();
info.bmiHeader.biSize = (uint) Marshal.SizeOf(info.bmiHeader);
info.bmiHeader.biWidth = 320;
info.bmiHeader.biHeight = 240;
info.bmiHeader.biPlanes = 1;
info.bmiHeader.biBitCount = 8;
info.bmiHeader.biCompression = BI_RGB;
info.bmiHeader.biSizeImage = 0;
info.bmiHeader.biClrUsed = 256;
info.bmiHeader.biClrImportant = 0;
// next line throws wrong parameter exception all the time
// SetDIBits(bitmapDC, bh, 0, 240, Marshal.UnsafeAddrOfPinnedArrayElement(info.bmiColors, 0), ref info, DIB_PAL_COLORS);
// how do i store all pixels into the bitmap at once ?
for (int i = 0; i < bytes.Length;i++)
SetPixel(bitmapDC, i % 320, i / 320, random(0x1000000));
// draw the bitmap
BitBlt(desktopDC, 0, 0, 320, 240, bitmapDC, 0, 0, SRCCOPY);
When I just try to set each pixel by itself with SetPixel() I see a monochrome image without gray colors only black and white. How can I correctly create a gray scale bitmap for displaying ? And how do I do that quick ?
Update:
The call ends up in an error outside of my program in WinApi. Can't catch exception:
public const int DIB_RGB_COLORS = 0;
public const int DIB_PAL_COLORS = 1;
[DllImport("gdi32.dll")]
public static extern int SetDIBits(IntPtr hdc, IntPtr hbmp, uint uStartScan, uint cScanLines, byte[] lpvBits, [In] ref BITMAPINFO lpbmi, uint fuColorUse);
// parameters as above
SetDIBits(bitmapDC, bitmap, 0, 240, bytes, ref info, DIB_RGB_COLORS);
Two of the SetDIBits parameters are wrong:
lpvBits - this is the image data but you're passing the palette data. You should be passing your bytes array.
lpBmi - this is OK - the BITMAPINFO structure contains both the BITMAPINFOHEADER and the palette so you don't need to pass the palette separately. My answer to your other question describes how to declare the structure.
fuColorUse - this describes the format of the palette. You are using an RGB palette so you should pass DIB_RGB_COLORS.