Open Source Computer Vision Library https://opencv.org/
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 

97 lines
3.7 KiB

# C++ wrappers for OpenVX-1.x C API
## Core ideas:
* lightweight - minimal overhead vs standard C API
* automatic references counting
* exceptions instead of return codes
* object-oriented design
* (NYI) helpers for user-defined kernels & nodes
* C++ 11 friendly
## Quick start sample
The following short sample gives basic knowledges on the wrappers usage:
```cpp
#include "ivx.hpp"
#include "ivx_lib_debug.hpp" // ivx::debug::*
int main()
{
vx_uint32 width = 640, height = 480;
try
{
ivx::Context context = ivx::Context::create();
ivx::Graph graph = ivx::Graph::create(context);
ivx::Image
gray = ivx::Image::create(context, width, height, VX_DF_IMAGE_U8),
gb = ivx::Image::createVirtual(graph),
res = ivx::Image::create(context, width, height, VX_DF_IMAGE_U8);
context.loadKernels("openvx-debug"); // ivx::debug::*
ivx::debug::fReadImage(context, inputPath, gray);
ivx::Node::create(graph, VX_KERNEL_GAUSSIAN_3x3, gray, gb);
ivx::Node::create(
graph,
VX_KERNEL_THRESHOLD,
gb,
ivx::Threshold::createBinary(context, VX_TYPE_UINT8, 50),
res
);
graph.verify();
graph.process();
ivx::debug::fWriteImage(context, res, "ovx-res-cpp.pgm");
}
catch (const ivx::RuntimeError& e)
{
printf("ErrorRuntime: code = %d(%x), message = %s\n", e.status(), e.status(), e.what());
return e.status();
}
catch (const ivx::WrapperError& e)
{
printf("ErrorWrapper: message = %s\n", e.what());
return -1;
}
catch(const std::exception& e)
{
printf("runtime_error: message = %s\n", e.what());
return -1;
}
return 0;
}
```
## C++ API overview
The wrappers have **header-only** implementation that simplifies their integration to projects.
All the API is inside `ivx` namespace (E.g. `class ivx::Graph`).
While the C++ API is pretty much the same for underlying OpenVX version **1.0** and **1.1**, there are alternative code branches for some features implementation that are selected at **compile time** via `#ifdef` preprocessor directives.
E.g. external ref-counting is implemented for 1.0 version and native OpenVX one is used (via `vxRetainReference()` and `vxReleaseXYZ()`) for version 1.1.
Also there are some **C++ 11** features are used (e.g. rvalue ref-s) when their availability is detected at ***compile time***.
C++ exceptions are used for errors indication instead of return codes. There are two types of exceptions are defined: `RuntimeError` is thrown when OpenVX C call returned unsuccessful result and `WrapperError` is thrown when a problem is occurred in the wrappers code. Both exception calsses are derived from `std::exception` (actually from its inheritants).
The so called **OpenVX objects** (e.g. `vx_image`) are represented as C++ classes in wrappers.
All these classes use automatic ref-counting that allows development of exception-safe code.
All these classes have `create()` or `createXYZ()` `static` methods for instances creation. (E.g. `Image::create()`, `Image::createVirtual()` and `Image::createFromHandle()`)
Most of the wrapped OpenVX functions are represented as methods of the corresponding C++ classes, but in most cases they still accept C "object" types (e.g. `vx_image` or `vx_context`) that allows mixing of C and C++ OpenVX API use.
E.g.:
```cpp
class Image
{
static Image create(vx_context context, vx_uint32 width, vx_uint32 height, vx_df_image format);
static Image createVirtual(vx_graph graph, vx_uint32 width = 0, vx_uint32 height = 0, vx_df_image format = VX_DF_IMAGE_VIRT);
// ...
}
```
All the classes instances can automatically be converted to the corresponding C "object" types.
For more details please refer to C++ wrappers reference manual or directly to their source code.