Add support for the HDRExtendedSrgbLinear color space on Metal

Request 16 bit floating point backbuffers and set the color space
of the CAMetalLayer to kCGColorSpaceExtendedLinearSRGB if we set
up the swap chain to use extended SRGB.

Unfortunately the required CAMetalLayer.wantsExtendedDynamicRangeContent
property is not yet available on iOS, so for now this is a macOS
only feature.

Change-Id: I28ab12cc0b829eded721061da2679be8e31d6b9d
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

2 files changed, 43 insertions, 0 deletions

diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index be38e92bcc..8ae5e25ffa 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -4033,6 +4033,10 @@ QSize QMetalSwapChain::surfacePixelSize()
 
 bool QMetalSwapChain::isFormatSupported(Format f)
 {
+#ifdef Q_OS_MACOS
+    if (@available(macOS 10.12, /*iOS 10.0,*/ *))
+        return f == SDR || f == HDRExtendedSrgbLinear;
+#endif
     return f == SDR;
 }
 
@@ -4064,6 +4068,13 @@ void QMetalSwapChain::chooseFormats()
     QRHI_RES_RHI(QRhiMetal);
     samples = rhiD->effectiveSampleCount(m_sampleCount);
     // pick a format that is allowed for CAMetalLayer.pixelFormat
+    if (m_format == HDRExtendedSrgbLinear) {
+        if (@available(macOS 10.12, /*iOS 10.0,*/ *)) {
+            d->colorFormat = MTLPixelFormatRGBA16Float;
+            d->rhiColorFormat = QRhiTexture::RGBA16F;
+            return;
+        }
+    }
     d->colorFormat = m_flags.testFlag(sRGB) ? MTLPixelFormatBGRA8Unorm_sRGB : MTLPixelFormatBGRA8Unorm;
     d->rhiColorFormat = QRhiTexture::BGRA8;
 }
@@ -4095,6 +4106,14 @@ bool QMetalSwapChain::createOrResize()
     chooseFormats();
     if (d->colorFormat != d->layer.pixelFormat)
         d->layer.pixelFormat = d->colorFormat;
+#ifdef Q_OS_MACOS
+    if (@available(macOS 10.12, /*iOS 10.0,*/ *)) { // Can't enable this on iOS until wantsExtendedDynamicRangeContent is available
+        if (m_format == HDRExtendedSrgbLinear) {
+            d->layer.colorspace = CGColorSpaceCreateWithName(kCGColorSpaceExtendedLinearSRGB);
+            d->layer.wantsExtendedDynamicRangeContent = YES;
+        }
+    }
+#endif
 
     if (m_flags.testFlag(UsedAsTransferSource))
         d->layer.framebufferOnly = NO;
@@ -4189,4 +4208,26 @@ bool QMetalSwapChain::createOrResize()
     return true;
 }
 
+QRhiSwapChainHdrInfo QMetalSwapChain::hdrInfo()
+{
+    QRhiSwapChainHdrInfo info;
+    info.limitsType = QRhiSwapChainHdrInfo::ColorComponentValue;
+    if (m_format == SDR) {
+        info.limits.colorComponentValue.maxColorComponentValue = 1;
+        return info;
+    }
+
+#ifdef Q_OS_MACOS
+    info.isHardCodedDefaults = false;
+    NSView *view = reinterpret_cast<NSView *>(window->winId());
+    info.limits.colorComponentValue.maxColorComponentValue = view.window.screen.maximumExtendedDynamicRangeColorComponentValue;
+#else
+    // ### Fixme: Maybe retrieve the brightness from the screen and if we're not at full brightness we might be able to do more.
+    // For now, assume 2, in line with iPhone 12 specs that claim 625 nits max brightness and 1200 nits max HDR brightness.
+    info.isHardCodedDefaults = true;
+    info.limits.colorComponentValue.maxColorComponentValue = 2;
+#endif
+    return info;
+}
+
 QT_END_NAMESPACE
diff --git a/src/gui/rhi/qrhimetal_p_p.h b/src/gui/rhi/qrhimetal_p_p.h
index cbb6e537b5..6ebddd20f5 100644
--- a/src/gui/rhi/qrhimetal_p_p.h
+++ b/src/gui/rhi/qrhimetal_p_p.h
@@ -330,6 +330,8 @@ struct QMetalSwapChain : public QRhiSwapChain
 
     bool createOrResize() override;
 
+    virtual QRhiSwapChainHdrInfo hdrInfo() override;
+
     void chooseFormats();
 
     QWindow *window = nullptr;