scenegraph: Allow requesting a HDR swapchain

...with an environment variable for now, to enable development and
testing.

Setting QSG_RHI_HDR to scrgb (or extendedsrgblinear) will request an
scRGB+RGBA16F swapchain. Setting it to hdr10 requests
HDR10(PQ)+A2RGB/BGR10. Otherwise the format stays the default SDR
RGBA/BGRA8.

When something is requested and is not supported for the window, print
a helpful message in the logs with QSG_INFO=1. When supported, the logs
will contain a Creating scRGB/HDR10 swapchain message.

In multi-screen configuration it is important to remember that the
position of the window may be important, depending on the windowing
system. Just having one HDR-enabled display does not mean the
application will launch with the requested HDR format - it may only be
successful if the window is positioned on that particular screen upon
startup. When in doubt, disable all non-HDR screens and try running with
the single HDR-enabled one.

Change-Id: Icf4994d86e39d0fafb3b1321229fc7be1500b372
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/quick/scenegraph/qsgthreadedrenderloop.cpp b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
index 985fd7fe0a..7311c77a6f 100644
--- a/src/quick/scenegraph/qsgthreadedrenderloop.cpp
+++ b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
@@ -947,6 +947,7 @@ void QSGRenderThread::ensureRhi()
             cd->swapchain->setDepthStencil(cd->depthStencilForSwapchain);
         }
         cd->swapchain->setWindow(window);
+        QSGRhiSupport::instance()->applySwapChainFormat(cd->swapchain);
         qCDebug(QSG_LOG_INFO, "MSAA sample count for the swapchain is %d. Alpha channel requested = %s.",
                 rhiSampleCount, alpha ? "yes" : "no");
         cd->swapchain->setSampleCount(rhiSampleCount);