OpenGL interoperability

General Information

This section describes OpenGL interoperability.

To enable OpenGL support, configure OpenCV using CMake with WITH_OPENGL=ON . Currently OpenGL is supported only with WIN32, GTK and Qt backends on Windows and Linux (MacOS and Android are not supported). For GTK backend gtkglext-1.0 library is required.

To use OpenGL functionality you should first create OpenGL context (window or frame buffer). You can do this with namedWindow() function or with other OpenGL toolkit (GLUT, for example).

ogl::Buffer

Smart pointer for OpenGL buffer object with reference counting.

class ogl::Buffer

Buffer Objects are OpenGL objects that store an array of unformatted memory allocated by the OpenGL context. These can be used to store vertex data, pixel data retrieved from images or the framebuffer, and a variety of other things.

ogl::Buffer has interface similar with Mat interface and represents 2D array memory.

ogl::Buffer supports memory transfers between host and device and also can be mapped to CUDA memory.

ogl::Buffer::Target

The target defines how you intend to use the buffer object.

C++: enum ogl::Buffer::Target
ARRAY_BUFFER

The buffer will be used as a source for vertex data.

ELEMENT_ARRAY_BUFFER

The buffer will be used for indices (in glDrawElements or ogl::render(), for example).

PIXEL_PACK_BUFFER

The buffer will be used for reading from OpenGL textures.

PIXEL_UNPACK_BUFFER

The buffer will be used for writing to OpenGL textures.

ogl::Buffer::Buffer

The constructors.

C++: ogl::Buffer::Buffer()
C++: ogl::Buffer::Buffer(int arows, int acols, int atype, unsigned int abufId, bool autoRelease=false)
C++: ogl::Buffer::Buffer(Size asize, int atype, unsigned int abufId, bool autoRelease=false)
C++: ogl::Buffer::Buffer(int arows, int acols, int atype, Target target=ARRAY_BUFFER, bool autoRelease=false)
C++: ogl::Buffer::Buffer(Size asize, int atype, Target target=ARRAY_BUFFER, bool autoRelease=false)
C++: ogl::Buffer::Buffer(InputArray arr, Target target=ARRAY_BUFFER, bool autoRelease=false)
Parameters:
  • arows – Number of rows in a 2D array.
  • acols – Number of columns in a 2D array.
  • asize – 2D array size.
  • atype – Array type ( CV_8UC1, ..., CV_64FC4 ). See Mat for details.
  • abufId – Buffer object name.
  • arr – Input array (host or device memory, it can be Mat , cuda::GpuMat or std::vector ).
  • target – Buffer usage. See ogl::Buffer::Target .
  • autoRelease – Auto release mode (if true, release will be called in object’s destructor).

Creates empty ogl::Buffer object, creates ogl::Buffer object from existed buffer ( abufId parameter), allocates memory for ogl::Buffer object or copies from host/device memory.

ogl::Buffer::create

Allocates memory for ogl::Buffer object.

C++: void ogl::Buffer::create(int arows, int acols, int atype, Target target=ARRAY_BUFFER, bool autoRelease=false)
C++: void ogl::Buffer::create(Size asize, int atype, Target target=ARRAY_BUFFER, bool autoRelease=false)
Parameters:
  • arows – Number of rows in a 2D array.
  • acols – Number of columns in a 2D array.
  • asize – 2D array size.
  • atype – Array type ( CV_8UC1, ..., CV_64FC4 ). See Mat for details.
  • target – Buffer usage. See ogl::Buffer::Target .
  • autoRelease – Auto release mode (if true, release will be called in object’s destructor).

ogl::Buffer::release

Decrements the reference counter and destroys the buffer object if needed.

C++: void ogl::Buffer::release()

The function will call setAutoRelease(true) .

ogl::Buffer::setAutoRelease

Sets auto release mode.

C++: void ogl::Buffer::setAutoRelease(bool flag)
Parameters:
  • flag – Auto release mode (if true, release will be called in object’s destructor).

The lifetime of the OpenGL object is tied to the lifetime of the context. If OpenGL context was bound to a window it could be released at any time (user can close a window). If object’s destructor is called after destruction of the context it will cause an error. Thus ogl::Buffer doesn’t destroy OpenGL object in destructor by default (all OpenGL resources will be released with OpenGL context). This function can force ogl::Buffer destructor to destroy OpenGL object.

ogl::Buffer::copyFrom

Copies from host/device memory to OpenGL buffer.

C++: void ogl::Buffer::copyFrom(InputArray arr, Target target=ARRAY_BUFFER, bool autoRelease=false)
Parameters:
  • arr – Input array (host or device memory, it can be Mat , cuda::GpuMat or std::vector ).
  • target – Buffer usage. See ogl::Buffer::Target .
  • autoRelease – Auto release mode (if true, release will be called in object’s destructor).

ogl::Buffer::copyTo

Copies from OpenGL buffer to host/device memory or another OpenGL buffer object.

C++: void ogl::Buffer::copyTo(OutputArray arr) const
Parameters:
  • arr – Destination array (host or device memory, can be Mat , cuda::GpuMat , std::vector or ogl::Buffer ).

ogl::Buffer::clone

Creates a full copy of the buffer object and the underlying data.

C++: Buffer ogl::Buffer::clone(Target target=ARRAY_BUFFER, bool autoRelease=false) const
Parameters:
  • target – Buffer usage for destination buffer.
  • autoRelease – Auto release mode for destination buffer.

ogl::Buffer::bind

Binds OpenGL buffer to the specified buffer binding point.

C++: void ogl::Buffer::bind(Target target) const
Parameters:

ogl::Buffer::unbind

Unbind any buffers from the specified binding point.

C++: static void ogl::Buffer::unbind(Target target)
Parameters:

ogl::Buffer::mapHost

Maps OpenGL buffer to host memory.

C++: Mat ogl::Buffer::mapHost(Access access)
Parameters:
  • access – Access policy, indicating whether it will be possible to read from, write to, or both read from and write to the buffer object’s mapped data store. The symbolic constant must be ogl::Buffer::READ_ONLY , ogl::Buffer::WRITE_ONLY or ogl::Buffer::READ_WRITE .

mapHost maps to the client’s address space the entire data store of the buffer object. The data can then be directly read and/or written relative to the returned pointer, depending on the specified access policy.

A mapped data store must be unmapped with ogl::Buffer::unmapHost() before its buffer object is used.

This operation can lead to memory transfers between host and device.

Only one buffer object can be mapped at a time.

ogl::Buffer::unmapHost

Unmaps OpenGL buffer.

C++: void ogl::Buffer::unmapHost()

ogl::Buffer::mapDevice

Maps OpenGL buffer to CUDA device memory.

C++: cuda::GpuMat ogl::Buffer::mapDevice()

This operatation doesn’t copy data. Several buffer objects can be mapped to CUDA memory at a time.

A mapped data store must be unmapped with ogl::Buffer::unmapDevice() before its buffer object is used.

ogl::Buffer::unmapDevice

Unmaps OpenGL buffer.

C++: void ogl::Buffer::unmapDevice()

ogl::Texture2D

Smart pointer for OpenGL 2D texture memory with reference counting.

class ogl::Texture2D

ogl::Texture2D::Format

An Image Format describes the way that the images in Textures store their data.

C++: enum ogl::Texture2D::Format
NONE
DEPTH_COMPONENT
RGB
RGBA

ogl::Texture2D::Texture2D

The constructors.

C++: ogl::Texture2D::Texture2D()
C++: ogl::Texture2D::Texture2D(int arows, int acols, Format aformat, unsigned int atexId, bool autoRelease=false)
C++: ogl::Texture2D::Texture2D(Size asize, Format aformat, unsigned int atexId, bool autoRelease=false)
C++: ogl::Texture2D::Texture2D(int arows, int acols, Format aformat, bool autoRelease=false)
C++: ogl::Texture2D::Texture2D(Size asize, Format aformat, bool autoRelease=false)
C++: ogl::Texture2D::Texture2D(InputArray arr, bool autoRelease=false)
Parameters:
  • arows – Number of rows.
  • acols – Number of columns.
  • asize – 2D array size.
  • aformat – Image format. See ogl::Texture2D::Format .
  • arr – Input array (host or device memory, it can be Mat , cuda::GpuMat or ogl::Buffer ).
  • autoRelease – Auto release mode (if true, release will be called in object’s destructor).

Creates empty ogl::Texture2D object, allocates memory for ogl::Texture2D object or copies from host/device memory.

ogl::Texture2D::create

Allocates memory for ogl::Texture2D object.

C++: void ogl::Texture2D::create(int arows, int acols, Format aformat, bool autoRelease=false)
C++: void ogl::Texture2D::create(Size asize, Format aformat, bool autoRelease=false)
Parameters:
  • arows – Number of rows.
  • acols – Number of columns.
  • asize – 2D array size.
  • aformat – Image format. See ogl::Texture2D::Format .
  • autoRelease – Auto release mode (if true, release will be called in object’s destructor).

ogl::Texture2D::release

Decrements the reference counter and destroys the texture object if needed.

C++: void ogl::Texture2D::release()

The function will call setAutoRelease(true) .

ogl::Texture2D::setAutoRelease

Sets auto release mode.

C++: void ogl::Texture2D::setAutoRelease(bool flag)
Parameters:
  • flag – Auto release mode (if true, release will be called in object’s destructor).

The lifetime of the OpenGL object is tied to the lifetime of the context. If OpenGL context was bound to a window it could be released at any time (user can close a window). If object’s destructor is called after destruction of the context it will cause an error. Thus ogl::Texture2D doesn’t destroy OpenGL object in destructor by default (all OpenGL resources will be released with OpenGL context). This function can force ogl::Texture2D destructor to destroy OpenGL object.

ogl::Texture2D::copyFrom

Copies from host/device memory to OpenGL texture.

C++: void ogl::Texture2D::copyFrom(InputArray arr, bool autoRelease=false)
Parameters:
  • arr – Input array (host or device memory, it can be Mat , cuda::GpuMat or ogl::Buffer ).
  • autoRelease – Auto release mode (if true, release will be called in object’s destructor).

ogl::Texture2D::copyTo

Copies from OpenGL texture to host/device memory or another OpenGL texture object.

C++: void ogl::Texture2D::copyTo(OutputArray arr, int ddepth=CV_32F, bool autoRelease=false) const
Parameters:
  • arr – Destination array (host or device memory, can be Mat , cuda::GpuMat , ogl::Buffer or ogl::Texture2D ).
  • ddepth – Destination depth.
  • autoRelease – Auto release mode for destination buffer (if arr is OpenGL buffer or texture).

ogl::Texture2D::bind

Binds texture to current active texture unit for GL_TEXTURE_2D target.

C++: void ogl::Texture2D::bind() const

ogl::Arrays

Wrapper for OpenGL Client-Side Vertex arrays.

class ogl::Arrays

ogl::Arrays stores vertex data in ogl::Buffer objects.

ogl::Arrays::setVertexArray

Sets an array of vertex coordinates.

C++: void ogl::Arrays::setVertexArray(InputArray vertex)
Parameters:
  • vertex – array with vertex coordinates, can be both host and device memory.

ogl::Arrays::resetVertexArray

Resets vertex coordinates.

C++: void ogl::Arrays::resetVertexArray()

ogl::Arrays::setColorArray

Sets an array of vertex colors.

C++: void ogl::Arrays::setColorArray(InputArray color)
Parameters:
  • color – array with vertex colors, can be both host and device memory.

ogl::Arrays::resetColorArray

Resets vertex colors.

C++: void ogl::Arrays::resetColorArray()

ogl::Arrays::setNormalArray

Sets an array of vertex normals.

C++: void ogl::Arrays::setNormalArray(InputArray normal)
Parameters:
  • normal – array with vertex normals, can be both host and device memory.

ogl::Arrays::resetNormalArray

Resets vertex normals.

C++: void ogl::Arrays::resetNormalArray()

ogl::Arrays::setTexCoordArray

Sets an array of vertex texture coordinates.

C++: void ogl::Arrays::setTexCoordArray(InputArray texCoord)
Parameters:
  • texCoord – array with vertex texture coordinates, can be both host and device memory.

ogl::Arrays::resetTexCoordArray

Resets vertex texture coordinates.

C++: void ogl::Arrays::resetTexCoordArray()

ogl::Arrays::release

Releases all inner buffers.

C++: void ogl::Arrays::release()

ogl::Arrays::setAutoRelease

Sets auto release mode all inner buffers.

C++: void ogl::Arrays::setAutoRelease(bool flag)
Parameters:
  • flag – Auto release mode.

ogl::Arrays::bind

Binds all vertex arrays.

C++: void ogl::Arrays::bind() const

ogl::Arrays::size

Returns the vertex count.

C++: int ogl::Arrays::size() const

ogl::render

Render OpenGL texture or primitives.

C++: void ogl::render(const Texture2D& tex, Rect_<double> wndRect=Rect_<double>(0.0, 0.0, 1.0, 1.0), Rect_<double> texRect=Rect_<double>(0.0, 0.0, 1.0, 1.0))
C++: void ogl::render(const Arrays& arr, int mode=POINTS, Scalar color=Scalar::all(255))
C++: void ogl::render(const Arrays& arr, InputArray indices, int mode=POINTS, Scalar color=Scalar::all(255))
Parameters:
  • tex – Texture to draw.
  • wndRect – Region of window, where to draw a texture (normalized coordinates).
  • texRect – Region of texture to draw (normalized coordinates).
  • arr – Array of privitives vertices.
  • indices – Array of vertices indices (host or device memory).
  • mode

    Render mode. Available options:

    • POINTS
    • LINES
    • LINE_LOOP
    • LINE_STRIP
    • TRIANGLES
    • TRIANGLE_STRIP
    • TRIANGLE_FAN
    • QUADS
    • QUAD_STRIP
    • POLYGON
  • color – Color for all vertices. Will be used if arr doesn’t contain color array.

cuda::setGlDevice

Sets a CUDA device and initializes it for the current thread with OpenGL interoperability.

C++: void cuda::setGlDevice(int device=0 )
Parameters:
  • device – System index of a CUDA device starting with 0.

This function should be explicitly called after OpenGL context creation and before any CUDA calls.