I try to control USB camera with libuvc on Ubuntu 20.04.
when the ctrl value = 0x400 and the unit value = 0x200,
I can call uvc_set_ctrl(device_handle, 0x4, 0x2, output_buffer, buffer_length), and it's successful to set value to specify register.
But how can I offer value to uvc_set_ctrl() when the unit value = 0x303?
These are library-specific functions -- different implementations of UVC (for example on Windows) won't have these, so I think your question would be better suited to the libuvc forum.
For what it's worth, I tried looking at the libuvc documentation to read about uvc_set_ctrl, but the URL for the documentation on the README page isn't valid anymore: https://int80k.com/libuvc/doc/
Related
According to the documentation, QCameraInfo::availableCameras should return list of available cameras. There's no catch to it according to the docs.
But still, I have two webcams and the array of available cameras is returned empty. What can I do? Is this even in the scope of programming, or does this mean Qt only supports limited subset of webcams?
The OS I'm using right now is Windows 7x64.
I have this Problem too.Then I read about the example.
I found that once you have declared QCamera object.it will return the right info.
Like this :`
QCamera *cam = new QCamera;
qDebug()<<QCameraInfo::availableCameras().count();`
I have one camera,so it returns 1 at last;
Try to copy the mediaservice plugin folder into your application dir (where the exe resides).
At least that solved this specific problem for me.
You need to resolve your dependencies (like Thomas D. mentioned).
(take a look at http://doc.qt.io/qt-5/windows-deployment.html )
From yourpathof\Qt\...subdir...\bin
execute
windeployqt.exe --debug YOURPATH\Debug
or
windeployqt.exe YOURPATH\Debug
I'm trying to reach a web page on an embedded device.
I'm using WinHttp on Win32.
When trying to read response I get error
ERROR_WINHTTP_INVALID_SERVER_RESPONSE
12152
The server response cannot be parsed.
But when I captured with WireShark I can see that response is coming.
So to test I wrote a simple C# program.
GetResponse was throwing exception
The server committed a protocol violation. Section=ResponseHeader
Detail=CR must be followed by LF
So according to below solution I set useUnsafeHeaderParsing to true. And it worked fine.
HttpWebRequestError: The server committed a protocol violation. Section=ResponseHeader Detail=CR must be followed by LF
Since I can't use C# I need to find a way to set useUnsafeHeaderParsing to true for WinHttp with win32 C++
Many thanks
I've briefly looked into the option flags of WinHttpSetOption and found the following entry:
WINHTTP_OPTION_UNSAFE_HEADER_BLOCKING
This option is reserved for internal use and should not be called.
Since the option looks linke an on/off switch I would try to do the following:
BOOL bResult;
BOOL bOption = FALSE;
bResult = WinHttpSetOption(hInternet,
WINHTTP_OPTION_UNSAFE_HEADER_BLOCKING,
&bOption,
sizeof(bOption));
if (bResult == FALSE)
{
/* handle error with GetLastError() */
}
Well but as MSDN says it's reserved for internal use and therefore the function may change in the future (or has already changed in the past). But it's worth a try... Good Luck!
Looks like the name of the option must have changed since then: with the current SDK it's WINHTTP_OPTION_UNSAFE_HEADER_PARSING. Also, I verified (by examining the Assembly code directly) that:
the option must be DWORD-sized
the value of the option doesn't matter, as long as it's nonzero
you can only enable unsafe parsing; trying to disable (by setting the option value to zero) causes an error to be returned
Obviously, since this undocumented, it's subject to change.
I have a code written in Atmel Studio to read/write data from a SD card. I am using FatFs here. My problem is the code doesn't compile when I use some of the functions (f_chdir, f_getcwd...) in FatFs. Some functions works fine (f_puts, f_open, f_mount, f_mkdir...). All these functions are located in same header file (ff.h, ff.c)
The error says "undefined reference to -function-, ld returned 1 exit status". When I go to the error it shows the end of the code while it is suppose to show where the error is.
I cannot understand the problem with my code. Any help is appreciated.
Just ran into this using the SD card for a project using SAM4S Xplained Pro (Atmel 7, ASF 3.20).
Make sure you have all the asf projects (fatfs, sd_mmc, memory access control, and then the other basics e.g. pmc, gpio, and maybe a few more). My asf did NOT include sd_mmc_mem.c and sd_mmc_mem.h for some reason, so I had to include those myself. Also remember to do the sd_mmc_init() at the top of your main loop. As for the configuration...
If you look closely at ffconf.h, the first thing it does is include conf_fatfs.h, which (wait for it!) is EXACTLY the same file line by line as ffconf.h. All the variables are defined there first and foremost (and guarded by an #ifndef FFCONF and NOT an CONF_FATFS) aka that's where it counts..
Go into conf_fatfs.h and change _USE_STRFUNC to 1 or 2 et voila.
Also note that in the places where you use it, you'll have to #include the ff.h preceded by either ffconf.h or conf_access.h
ASF is a real snake pit if you don't know what you're looking for.
Enjoy.
By default, the memory control access interface is disabled in the ASF wizard. In order to enable the memory control access, please follow the steps below.
Open the ASF wizard (Alt + W).
Enable the Memory Control Access as follows.
ASF SD sd_mmc_mem.h memory access enable
Finally, click the “Apply” option to make the changes.
This adds sd_mmc_mem.h /.c files
Open the ffconf.h in your favorite editor and set _FS_RPATH to 2. From ffconf.h:
#define _FS_RPATH 0
/* This option configures relative path feature.
/
/ 0: Disable relative path feature and remove related functions.
/ 1: Enable relative path feature. f_chdir() and f_chdrive() are available.
/ 2: f_getcwd() function is available in addition to 1.
/
/ Note that directory items read via f_readdir() are affected by this option. */
Which features of the fatfs library are included in your build is configurable, so that you don't have to lose valuable ROM space (as well as a few bytes of RAM) for functions you're not using.
For versions of the FatFS library prior to 0.8a, _FS_RPATH supports only values 0 and 1; f_getcwd is not available in these versions.
Additionally, in versions prior to 0.8, it is necessary for C++ code to explicitly include its headers as C headers to avoid name mangling:
extern "C" {
#include "ff.h"
}
From version 0.8 onwards, it does this internally. You can find the new versions here if you're still working with an old one -- the comment you left leads me to believe that this might be the case.
Check if _FS_MINIMZE in ffconf.h is 0 to have all functions available.
In my version that I downloaded from elm-chan it was by default set to 3 and lead to the compiler error: undefined reference.
In file ffconf.h, set #define _USE_FIND to 1.
/* This option switches filtered directory read functions, f_findfirst() and
/ f_findnext(). (0:Disable, 1:Enable 2:Enable with matching altname[] too) */
I needed to use f_findfirst() and f_findnext() functions and i was getting undefined reference errors.
Now this solved my problem.
Drive/directory handling functions are under #if _FS_RPATH >= 1 (or similar preprocessors) .
Say I have an application I write, that relies for some task on an externat app (lets call it "tool") that is installed on my machine. In my program, I call it with system( "tool myarguments" ); , works fine.
Now, I want to distribute my app. Of course, the end-user might not have "tool" installed on his machine, so I would like my app to check this, and printout a message for the user. So my question is:
Is there a portable way to check for the existence of an app on the machine? (assuming we know its name and it is accessible through the machine's shell).
Additional information: First idea was to check the existence of the binary file, but:
This is platform dependent,
depending on how it has been installed (build from sources, installed through package,...), it might not always be in the same place, although it can be accessed through local path.
My first opinion on this question is "No", but maybe somebody has an idea ?
Reference: system()
Related: stackoverflow.com/questions/7045879
If you use the Qt toolkit, QProcess may help you.
Edit: and look for QProcess::error() return value: if it is QProcess::FailedToStart , then either it is not installed, or you have insufficient permissions.
If running the tool without argument has no side-effect, and is expected to return an exit code of 0, you can use system("tool") to check tool's existence.
You can check whether the command has been found by checking system's return value like this:
int ret = system("tool");
if (ret != 0) {
std::cout << "tool is not here, move along\n";
}
It is portable in the sense that system is expected to return 0 if all goes well and the command return status is 0 too.
For example, on Linux, running system("non_existing_command") returns 0x7F00 (same type of value as returned by wait()).
On Windows, it returns 1 instead.
I am using TWAIN in C++ and I am trying to set the DPI manually so that a user is not displayed with the scan dialog but instead the page just scans with set defaults and is stored for them. I need to set the DPI manually but I can not seem to get it to work. I have tried setting the capability using the ICAP_XRESOLUTION and the ICAP_YRESOLUTION. When I look at the image's info though it always shows the same resolution no matter what I set it to using the ICAPs. Is there another way to set the resolution of a scanned in image or is there just an additional step that needs to be done that I can not find in the documentation anywhere?
Thanks
I use ICAP_XRESOLUTION and the ICAP_YRESOLUTION to set the scan resolution for a scanner, and it works at least for a number of HP scanners.
Code snipset:
float x_res = 1200;
cap.Cap = ICAP_XRESOLUTION;
cap.ConType = TWON_ONEVALUE;
cap.hContainer = GlobalAlloc(GHND, sizeof(TW_ONEVALUE));
if(cap.hContainer)
{
val_p = (pTW_ONEVALUE)GlobalLock(cap.hContainer);
val_p->ItemType = TWTY_FIX32;
TW_FIX32 fix32_val = FloatToFIX32(x_res);
val_p->Item = *((pTW_INT32) &fix32_val);
GlobalUnlock(cap.hContainer);
ret_code = SetCapability(cap);
GlobalFree(cap.hContainer);
}
TW_FIX32 FloatToFIX32(float i_float)
{
TW_FIX32 Fix32_value;
TW_INT32 value = (TW_INT32) (i_float * 65536.0 + 0.5);
Fix32_value.Whole = LOWORD(value >> 16);
Fix32_value.Frac = LOWORD(value & 0x0000ffffL);
return Fix32_value;
}
The value should be of type TW_FIX32 which is a floating point format defined by twain (strange but true).
I hope it works for you!
It should work the way.
But unfortunately we're not living in a perfect world. TWAIN drivers are among the most buggy drivers out there. Controlling the scanning process with TWAIN has always been a big headache because most drivers have never been tested without the scan dialog.
As far as I know there is also no test-suite for twain-drivers, so each of them will behave slightly different.
I wrote an OCR application back in the 90th and had to deal with these issues as well. What I ended up was having a list of supported scanners and a scanner module with lots of hacks and work-arounds for each different driver.
Take the ICAP_XRESOLUTION for example: The TWAIN documentation sais you have to send the resolution as a 32 bit float. Have you tried to set it using an integer instead? Or send it as float but put the bit-representation of an integer into the float, or vice versa. All this could work for the driver you're working with. Or it could not work at all.
I doubt the situation has changed much since then. So good luck getting it working on at least half of the machines that are out there.