backends/drm: ensure correct colors with direct scanout of NV12 buffers

If another compositor changes the color encoding and color range properties, the
resulting colors will be wrong. This commit ensures they're always set to BT.709
limited range to prevent that

src/backends/drm/drm_pipeline.cpp

@@ -249,8 +249,17 @@ DrmPipeline::Error DrmPipeline::prepareAtomicPresentation(DrmAtomicCommit *commi
     if (!fb) {
         return Error::InvalidArguments;
     }
-    m_pending.crtc->primaryPlane()->set(commit, QPoint(0, 0), fb->buffer()->size(), centerBuffer(fb->buffer()->size(), m_pending.mode->size()));
+    const auto primary = m_pending.crtc->primaryPlane();
+    primary->set(commit, QPoint(0, 0), fb->buffer()->size(), centerBuffer(fb->buffer()->size(), m_pending.mode->size()));
     commit->addBuffer(m_pending.crtc->primaryPlane(), fb);
+    if (fb->buffer()->dmabufAttributes()->format == DRM_FORMAT_NV12) {
+        if (!primary->colorEncoding.isValid() || !primary->colorRange.isValid()) {
+            // don't allow NV12 direct scanout if we don't know what the driver will do
+            return Error::InvalidArguments;
+        }
+        commit->addEnum(primary->colorEncoding, DrmPlane::ColorEncoding::BT701_YCbCr);
+        commit->addEnum(primary->colorRange, DrmPlane::ColorRange::Limited_YCbCr);
+    }
     return Error::None;
 }
 

src/backends/drm/drm_plane.cpp

@@ -54,6 +54,15 @@ DrmPlane::DrmPlane(DrmGpu *gpu, uint32_t planeId)
                                                                       QByteArrayLiteral("Pre-multiplied"),
                                                                       QByteArrayLiteral("Coverage"),
                                                                   })
+    , colorEncoding(this, QByteArrayLiteral("COLOR_ENCODING"), {
+                                                                   QByteArrayLiteral("ITU-R BT.601 YCbCr"),
+                                                                   QByteArrayLiteral("ITU-R BT.709 YCbCr"),
+                                                                   QByteArrayLiteral("ITU-R BT.2020 YCbCr"),
+                                                               })
+    , colorRange(this, QByteArrayLiteral("COLOR_RANGE"), {
+                                                             QByteArrayLiteral("YCbCr limited range"),
+                                                             QByteArrayLiteral("YCbCr full range"),
+                                                         })
 {
 }
 
@@ -80,6 +89,8 @@ bool DrmPlane::updateProperties()
     inFormats.update(props);
     alpha.update(props);
     pixelBlendMode.update(props);
+    colorEncoding.update(props);
+    colorRange.update(props);
 
     if (!type.isValid() || !srcX.isValid() || !srcY.isValid() || !srcW.isValid() || !srcH.isValid()
         || !crtcX.isValid() || !crtcY.isValid() || !crtcW.isValid() || !crtcH.isValid() || !fbId.isValid()) {

src/backends/drm/drm_plane.h

@@ -61,6 +61,15 @@ public:
         PreMultiplied,
         Coverage
     };
+    enum class ColorEncoding : uint64_t {
+        BT601_YCbCr,
+        BT701_YCbCr,
+        BT2020_YCbCr
+    };
+    enum class ColorRange : uint64_t {
+        Limited_YCbCr,
+        Full_YCbCr
+    };
 
     DrmEnumProperty<TypeIndex> type;
     DrmProperty srcX;
@@ -77,6 +86,8 @@ public:
     DrmProperty inFormats;
     DrmProperty alpha;
     DrmEnumProperty<PixelBlendMode> pixelBlendMode;
+    DrmEnumProperty<ColorEncoding> colorEncoding;
+    DrmEnumProperty<ColorRange> colorRange;
 
     static int32_t transformationToDegrees(Transformations transformation);