class QOpenGLTextureBlitter#

The QOpenGLTextureBlitter class provides a convenient way to draw textured quads via OpenGL. More…

Synopsis#

Methods#

def __init__()
def bind()
def blit()
def create()
def destroy()
def isCreated()
def release()
def setOpacity()
def setRedBlueSwizzle()
def supportsExternalOESTarget()
def supportsRectangleTarget()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

Drawing textured quads, in order to get the contents of a texture onto the screen, is a common operation when developing 2D user interfaces. QOpenGLTextureBlitter provides a convenience class to avoid repeating vertex data, shader sources, buffer and program management and matrix calculations.

For example, a QOpenGLWidget subclass can do the following to draw the contents rendered into a framebuffer at the pixel position (x, y):

void OpenGLWidget::initializeGL()
{
    m_blitter.create();
    m_fbo = new QOpenGLFramebufferObject(size);
}

void OpenGLWidget::paintGL()
{
    m_fbo->bind();
    // update offscreen content
    m_fbo->release();

    m_blitter.bind();
    const QRect targetRect(QPoint(x, y), m_fbo->size());
    const QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, QRect(QPoint(0, 0), m_fbo->size()));
    m_blitter.blit(m_fbo->texture(), target, QOpenGLTextureBlitter::OriginBottomLeft);
    m_blitter.release();
}

The blitter implements GLSL shaders both for GLSL 1.00 (suitable for OpenGL (ES) 2.x and compatibility profiles of newer OpenGL versions) and version 150 (suitable for core profile contexts with OpenGL 3.2 and newer).

class Origin#

Constant	Description
QOpenGLTextureBlitter.OriginBottomLeft	Indicates that the data in the texture follows the OpenGL convention of coordinate systems, meaning Y is running from bottom to top.
QOpenGLTextureBlitter.OriginTopLeft	Indicates that the data in the texture has Y running from top to bottom, which is typical with regular, unflipped image data.

See also

blit()

__init__()#

Constructs a new QOpenGLTextureBlitter instance.

Note

no graphics resources are initialized in the constructor. This makes it safe to place plain QOpenGLTextureBlitter members into classes because the actual initialization that depends on the OpenGL context happens only in create() .

bind([target=GL_TEXTURE_2D])#

Parameters:: target – int

Binds the graphics resources used by the blitter. This must be called before calling blit() . Code modifying the OpenGL state should be avoided between the call to bind() and blit() because otherwise conflicts may arise.

target is the texture target for the source texture and must be either GL_TEXTURE_2D, GL_TEXTURE_RECTANGLE, or GL_OES_EGL_image_external.

See also

release() blit()

blit(texture, targetTransform, sourceOrigin)#

Parameters:

texture – int
targetTransform – QMatrix4x4
sourceOrigin – Origin

blit(texture, targetTransform, sourceTransform)

Parameters:

texture – int
targetTransform – QMatrix4x4
sourceTransform – QMatrix3x3

create()#

Return type:: bool

Initializes the graphics resources used by the blitter.

Returns true if successful, false if there was a failure. Failures can occur when there is no OpenGL context current on the current thread, or when shader compilation fails for some reason.

See also

isCreated() destroy()

destroy()#

Frees all graphics resources held by the blitter. Assumes that the OpenGL context, or another context sharing resources with it, that was current on the thread when invoking create() is current.

The function has no effect when the blitter is not in created state.

See also

create()

isCreated()#

Return type:: bool

Returns true if create() was called and succeeded. false otherwise.

See also

create() destroy()

release()#

Unbinds the graphics resources used by the blitter.

See also

bind()

setOpacity(opacity)#

Parameters:: opacity – float

Changes the opacity to opacity. The default opacity is 1.0.

Note

the blitter does not alter the blend state. It is up to the caller of blit() to ensure the correct blend settings are active.

setRedBlueSwizzle(swizzle)#

Parameters:: swizzle – bool

Sets whether swizzling is enabled for the red and blue color channels to swizzle. An BGRA to RGBA conversion (occurring in the shader on the GPU, instead of a slow CPU-side transformation) can be useful when the source texture contains data from a QImage with a format like QImage::Format_ARGB32 which maps to BGRA on little endian systems.

By default the red-blue swizzle is disabled since this is what a texture attached to an framebuffer object or a texture based on a byte ordered QImage format (like QImage::Format_RGBA8888) needs.

static sourceTransform(subTexture, textureSize, origin)#

Parameters:

subTexture – QRectF
textureSize – QSize
origin – Origin

Return type:

QMatrix3x3

Calculates a 3x3 matrix suitable as the input to blit() . This is used when only a part of the texture is to be used in the blit.

subTexture is the desired source rectangle in pixels, textureSize is the full width and height of the texture data. origin specifies the orientation of the image data when it comes to the Y axis.

See also

blit() Origin

supportsExternalOESTarget()#

Return type:: bool

Returns true when bind() accepts GL_TEXTURE_EXTERNAL_OES as its target argument.

See also

bind() blit()

supportsRectangleTarget()#

Return type:: bool

Returns true when bind() accepts GL_TEXTURE_RECTANGLE as its target argument.

See also

bind() blit()

static targetTransform(target, viewport)#

Parameters:

target – QRectF
viewport – QRect

Return type:

QMatrix4x4

Calculates a target transform suitable for blit() .

target is the target rectangle in pixels. viewport describes the source dimensions and will in most cases be set to (0, 0, image width, image height).

For unscaled output the size of target and viewport should match.

See also

blit()