This will be used in RenderMode3D only in practice, where Qt Quick 3D
is going to pass in multiple matrices to the QSGRenderer.

Task-number: QTBUG-114871
Change-Id: Icae7f05958729d9e51948e1f38621ec4a541192d
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

We would pixel-align native text *before* applying the
model-view matrix, which would cause GL_NEAREST artifacts to
show up when the text was positioned at a subpixel offset in
some cases. Instead, we pixel-align the coordinates after mapping
them to the view frustum, but before applying the projection to the
screen.

To make it easier to modify the buffer layout for the shaders the
next time, this also adds some constants for offsets.

[ChangeLog][Text] Fixed an issue where text using NativeRendering
would look slightly skewed if it was inside a parent that had
been positioned at a subpixel offset.

Pick-to: 5.15 6.2
Fixes: QTBUG-96112
Fixes: QTBUG-83626
Task-number: QTBUG-55638
Change-Id: Ifb785ad5830093df94afc75a7bc288e24ca7aa38
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

Add the dpr-related modifications to the shaders used on the QRhi-based
rendering path.

Change-Id: Ice980a80cbf9910d06a95a957817ff3d689c5e0f
Fixes: QTBUG-80297
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

Opt in via environment variables:
QSG_RHI=1 -> enable using QRhi instead of GL
QSG_RHI_BACKEND -> set to vulkan, metal, d3d11, gl to override the default
(the default is d3d11 on Windows, metal on Mac, gl elsewhere)

Or force a given rhi backend via the existing
QQuickWindow::setSceneGraphBackend().

Otherwise the default behavior is the same as before, the rhi code path
is never active by default.

-no-opengl builds are supported in the sense that they work and default
to the software backend. However, the rhi code path cannot currently be
used in such builds, even though QRhi from qtbase is fully functional
with Vulkan, D3D, or Metal even when qtbase was configured with
-no-opengl. This cannot be utilized by Quick atm due to OpenGL usage
being all over the place in the sources corresponding to the default
backend, and those host the rhi code path as well. This will be cleaned up
hopefully in Qt 6, with the removal all direct OpenGL usage.

Other env.vars.:
QSG_RHI_DEBUG_LAYER=1 -> enable D3D debug or Vulkan validation layer
(assuming the system is set up for this)
QSG_RHI_SHADEREFFECT_DEBUG=1 -> print stuff from ShaderEffect
QSG_SAMPLES=1,2,4,... -> MSAA sample count (but QSurfaceFormat works too)
QT_D3D_ADAPTER_INDEX=0,1,... -> D3D adapter index
QT_VK_PHYSICAL_DEVICE_INDEX=0,1,... -> Vulkan physical device index
QSG_RHI_UINT32_INDEX=1 -> always use uint index data (both
merged/unmerged, convert when needed - with some rhi backends this is
implicit)
QSG_RENDER_LOOP -> to override the render loop as usual. The default
with RHI is threaded for Metal, threaded for Vulkan on Windows, basic
for Vulkan on Linux and Android (to be checked later), while the existing
rules apply for OpenGL.

Not supported when running with QRhi:
  - particles
  - compressed atlases (though this is transparent to the apps)
  - QSGRenderNode
  - QQuickRenderControl
  - QQuickFramebufferObject
  - certain QQuickWindow functionality that depends directly on OpenGL
  - anisotropic filtering for textures
  - native text may lack some gamma correction
  - QSGEngine applicability unclear
  - some QML profiler logs may be incorrect or irrelevant

Change-Id: I7822e99ad79e342e4166275da6e9e66498d76521
Reviewed-by: Lars Knoll <lars.knoll@qt.io>