mirror of
https://github.com/opencv/opencv.git
synced 2024-12-26 18:58:16 +08:00
98 lines
3.7 KiB
Markdown
98 lines
3.7 KiB
Markdown
# 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.
|