QSGTexture#

The QSGTexture class is the base class for textures used in the scene graph. More…

Synopsis#

Functions#

def anisotropyLevel ()
def convertToNormalizedSourceRect (rect)
def filtering ()
def horizontalWrapMode ()
def mipmapFiltering ()
def resolveInterface (name, revision)
def setAnisotropyLevel (level)
def setFiltering (filter)
def setHorizontalWrapMode (hwrap)
def setMipmapFiltering (filter)
def setVerticalWrapMode (vwrap)
def verticalWrapMode ()

Virtual functions#

def comparisonKey ()
def hasAlphaChannel ()
def hasMipmaps ()
def isAtlasTexture ()
def normalizedTextureSubRect ()
def textureSize ()

Detailed Description#

Users can freely implement their own texture classes to support arbitrary input textures, such as YUV video frames or 8 bit alpha masks. The scene graph provides a default implementation for RGBA textures.The default implementation is not instantiated directly, rather they are constructed via factory functions, such as createTextureFromImage() .

With the default implementation, each QSGTexture is backed by a QRhiTexture, which in turn contains a native texture object, such as an OpenGL texture or a Vulkan image.

The size in pixels is given by textureSize() . hasAlphaChannel() reports if the texture contains opacity values and hasMipmaps() reports if the texture contains mipmap levels.

Materials that work with textures reimplement updateSampledImage() to provide logic that decides which QSGTexture ‘s underlying native texture should be exposed at a given shader resource binding point.

QSGTexture does not separate image (texture) and sampler objects. The parameters for filtering and wrapping can be specified with setMipmapFiltering() , setFiltering() , setHorizontalWrapMode() and setVerticalWrapMode() . The scene graph and Qt’s graphics abstraction takes care of creating separate sampler objects, when applicable.

Texture Atlases#

Some scene graph backends use texture atlasses, grouping multiple small textures into one large texture. If this is the case, the function isAtlasTexture() will return true. Atlases are used to aid the rendering algorithm to do better sorting which increases performance. Atlases are also essential for batching (merging together geometry to reduce the number of draw calls), because two instances of the same material using two different QSGTextures are not batchable, whereas if both QSGTextures refer to the same atlas, batching can happen, assuming the materials are otherwise compatible.

The location of the texture inside the atlas is given with the normalizedTextureSubRect() function.

If the texture is used in such a way that atlas is not preferable, the function removedFromAtlas() can be used to extract a non-atlased copy.

Note

All classes with QSG prefix should be used solely on the scene graph’s rendering thread. See Scene Graph and Rendering for more information.

Constant	Description
QSGTexture.Repeat	Only the fractional part of the texture coordinate is used, causing values above 1 and below 0 to repeat.
QSGTexture.ClampToEdge	Values above 1 are clamped to 1 and values below 0 are clamped to 0.
QSGTexture.MirroredRepeat	When the texture coordinate is even, only the fractional part is used. When odd, the texture coordinate is set to `1 - fractional part`. This value has been introduced in Qt 5.10.

Constant	Description
QSGTexture.None	No filtering should occur. This value is only used together with `setMipmapFiltering()` .
QSGTexture.Nearest	Sampling returns the nearest texel.
QSGTexture.Linear	Sampling returns a linear interpolation of the neighboring texels.

Constant	Description
QSGTexture.AnisotropyNone	No anisotropic filtering.
QSGTexture.Anisotropy2x	2x anisotropic filtering.
QSGTexture.Anisotropy4x	4x anisotropic filtering.
QSGTexture.Anisotropy8x	8x anisotropic filtering.
QSGTexture.Anisotropy16x	16x anisotropic filtering.