QOpenGLTextureBlitter Class▲
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Header: QOpenGLTextureBlitter
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Since: Qt 5.8
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CMake:
find_package(Qt6 REQUIRED COMPONENTS OpenGL)
target_link_libraries(mytarget PRIVATE Qt6::OpenGL)
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qmake: QT += opengl
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Group: QOpenGLTextureBlitter is part of painting-3D
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).
Member Type Documentation▲
enum QOpenGLTextureBlitter::Origin▲
|
Constant |
Value |
Description |
|---|---|---|
|
QOpenGLTextureBlitter::OriginBottomLeft |
0 |
Indicates that the data in the texture follows the OpenGL convention of coordinate systems, meaning Y is running from bottom to top. |
|
QOpenGLTextureBlitter::OriginTopLeft |
1 |
Indicates that the data in the texture has Y running from top to bottom, which is typical with regular, unflipped image data. |
See Also▲
See also blit()
Member Function Documentation▲
QOpenGLTextureBlitter::QOpenGLTextureBlitter()▲
Constructs a new QOpenGLTextureBlitter instance.
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().
QOpenGLTextureBlitter::~QOpenGLTextureBlitter()▲
Destructs the instance.
void QOpenGLTextureBlitter::bind(GLenum target = GL_TEXTURE_2D)▲
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▲
void QOpenGLTextureBlitter::blit(GLuint texture, const QMatrix4x4 &targetTransform, QOpenGLTextureBlitter::Origin sourceOrigin)▲
Performs the blit with the source texture texture.
targetTransform specifies the transformation applied. This is usually generated by the targetTransform() helper function.
sourceOrigin specifies if the image data needs flipping. When texture corresponds to a texture attached to an FBO pass OriginBottomLeft. On the other hand, when texture is based on unflipped image data, pass OriginTopLeft. This is more efficient than using QImage::mirrored().
See Also▲
See also targetTransform(), Origin, bind()
void QOpenGLTextureBlitter::blit(GLuint texture, const QMatrix4x4 &targetTransform, const QMatrix3x3 &sourceTransform)▲
Performs the blit with the source texture texture.
targetTransform specifies the transformation applied. This is usually generated by the targetTransform() helper function.
sourceTransform specifies the transformation applied to the source. This allows using only a sub-rect of the source texture. This is usually generated by the sourceTransform() helper function.
See Also▲
See also sourceTransform(), targetTransform(), Origin, bind()
bool QOpenGLTextureBlitter::create()▲
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▲
void QOpenGLTextureBlitter::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▲
See also create()
bool QOpenGLTextureBlitter::isCreated() const▲
void QOpenGLTextureBlitter::release()▲
void QOpenGLTextureBlitter::setOpacity(float opacity)▲
Changes the opacity to opacity. The default opacity is 1.0.
the blitter does not alter the blend state. It is up to the caller of blit() to ensure the correct blend settings are active.
void QOpenGLTextureBlitter::setRedBlueSwizzle(bool swizzle)▲
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] QMatrix3x3 QOpenGLTextureBlitter::sourceTransform(const QRectF &subTexture, const QSize &textureSize, QOpenGLTextureBlitter::Origin origin)▲
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.