backends/drm: support cropping with direct scanout

src/backends/drm/drm_egl_layer.cpp

@@ -94,6 +94,13 @@ bool EglGbmLayer::scanout(SurfaceItem *surfaceItem)
         return false;
     }
     const auto surface = item->surface();
+    // kernel documentation says that
+    // "Devices that don’t support subpixel plane coordinates can ignore the fractional part."
+    // so we need to make sure that doesn't cause a difference vs the composited result
+    m_bufferSourceBox = surface->bufferSourceBox().toRect();
+    if (surface->bufferSourceBox() != m_bufferSourceBox) {
+        return false;
+    }
     const auto neededTransform = surface->bufferTransform().combine(m_pipeline->output()->transform().inverted());
     const auto plane = m_pipeline->crtc()->primaryPlane();
     if (neededTransform != OutputTransform::Kind::Normal && (!plane || !plane->supportsTransformation(neededTransform))) {
@@ -160,4 +167,9 @@ OutputTransform EglGbmLayer::hardwareTransform() const
 {
     return m_scanoutBuffer ? m_scanoutTransform : OutputTransform::Normal;
 }
+
+QRect EglGbmLayer::bufferSourceBox() const
+{
+    return m_scanoutBuffer ? m_bufferSourceBox : QRect(QPoint(0, 0), m_surface.currentBuffer()->buffer()->size());
+}
 }

src/backends/drm/drm_egl_layer.h

@@ -39,6 +39,7 @@ public:
     void releaseBuffers() override;
     std::chrono::nanoseconds queryRenderTime() const override;
     OutputTransform hardwareTransform() const override;
+    QRect bufferSourceBox() const override;
 
 private:
     std::shared_ptr<DrmFramebuffer> m_scanoutBuffer;
@@ -46,6 +47,7 @@ private:
     OutputTransform m_scanoutTransform = OutputTransform::Kind::Normal;
     // the output transform the buffer is made for
     OutputTransform m_scanoutBufferTransform = OutputTransform::Kind::Normal;
+    QRect m_bufferSourceBox;
     QRegion m_currentDamage;
 
     EglGbmLayerSurface m_surface;

src/backends/drm/drm_layer.cpp

@@ -7,6 +7,8 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 #include "drm_layer.h"
+#include "core/graphicsbuffer.h"
+#include "drm_buffer.h"
 #include "drm_pipeline.h"
 
 #include <QMatrix4x4>
@@ -36,4 +38,10 @@ OutputTransform DrmPipelineLayer::hardwareTransform() const
 {
     return OutputTransform::Kind::Normal;
 }
+
+QRect DrmPipelineLayer::bufferSourceBox() const
+{
+    const auto buffer = currentBuffer();
+    return buffer ? QRect(QPoint(0, 0), currentBuffer()->buffer()->size()) : QRect();
+}
 }

src/backends/drm/drm_layer.h

@@ -39,6 +39,7 @@ public:
     virtual bool checkTestBuffer() = 0;
     virtual std::shared_ptr<DrmFramebuffer> currentBuffer() const = 0;
     virtual OutputTransform hardwareTransform() const;
+    virtual QRect bufferSourceBox() const;
 
 protected:
     DrmPipeline *const m_pipeline;

src/backends/drm/drm_pipeline.cpp

@@ -266,7 +266,7 @@ DrmPipeline::Error DrmPipeline::prepareAtomicPresentation(DrmAtomicCommit *commi
     } else if (planeTransform != DrmPlane::Transformation::Rotate0) {
         return Error::InvalidArguments;
     }
-    primary->set(commit, QPoint(0, 0), fb->buffer()->size(), centerBuffer(transform.map(fb->buffer()->size()), m_pending.mode->size()));
+    primary->set(commit, m_primaryLayer->bufferSourceBox(), centerBuffer(transform.map(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()) {
@@ -283,13 +283,18 @@ void DrmPipeline::prepareAtomicCursor(DrmAtomicCommit *commit)
 {
     auto plane = m_pending.crtc->cursorPlane();
     const auto layer = cursorLayer();
-    plane->set(commit, QPoint(0, 0), gpu()->cursorSize(), QRect(layer->position().toPoint(), gpu()->cursorSize()));
-    commit->addProperty(plane->crtcId, layer->isEnabled() ? m_pending.crtc->id() : 0);
-    commit->addBuffer(plane, layer->isEnabled() ? layer->currentBuffer() : nullptr);
+    if (layer->isEnabled()) {
+        plane->set(commit, layer->bufferSourceBox(), QRect(layer->position().toPoint(), gpu()->cursorSize()));
+        commit->addProperty(plane->crtcId, m_pending.crtc->id());
+        commit->addBuffer(plane, layer->currentBuffer());
         if (plane->vmHotspotX.isValid() && plane->vmHotspotY.isValid()) {
             commit->addProperty(plane->vmHotspotX, std::round(layer->hotspot().x()));
             commit->addProperty(plane->vmHotspotY, std::round(layer->hotspot().y()));
         }
+    } else {
+        commit->addProperty(plane->crtcId, 0);
+        commit->addBuffer(plane, nullptr);
+    }
 }
 
 void DrmPipeline::prepareAtomicDisable(DrmAtomicCommit *commit)

src/backends/drm/drm_pipeline_legacy.cpp

@@ -30,6 +30,9 @@ DrmPipeline::Error DrmPipeline::presentLegacy()
         return err;
     }
     const auto buffer = m_primaryLayer->currentBuffer();
+    if (m_primaryLayer->bufferSourceBox() != QRect(QPoint(0, 0), buffer->buffer()->size())) {
+        return Error::InvalidArguments;
+    }
     auto commit = std::make_unique<DrmLegacyCommit>(this, buffer);
     if (!commit->doPageflip(m_pending.presentationMode)) {
         qCWarning(KWIN_DRM) << "Page flip failed:" << strerror(errno);
@@ -50,7 +53,11 @@ DrmPipeline::Error DrmPipeline::legacyModeset()
     if (!m_primaryLayer->checkTestBuffer()) {
         return Error::TestBufferFailed;
     }
-    auto commit = std::make_unique<DrmLegacyCommit>(this, m_primaryLayer->currentBuffer());
+    const auto buffer = m_primaryLayer->currentBuffer();
+    if (m_primaryLayer->bufferSourceBox() != QRect(QPoint(0, 0), buffer->buffer()->size())) {
+        return Error::InvalidArguments;
+    }
+    auto commit = std::make_unique<DrmLegacyCommit>(this, buffer);
     if (!commit->doModeset(m_connector, m_pending.mode.get())) {
         qCWarning(KWIN_DRM) << "Modeset failed!" << strerror(errno);
         return errnoToError();

src/backends/drm/drm_plane.cpp

@@ -126,14 +126,13 @@ bool DrmPlane::updateProperties()
     return true;
 }
 
-void DrmPlane::set(DrmAtomicCommit *commit, const QPoint &srcPos, const QSize &srcSize, const QRect &dst)
+void DrmPlane::set(DrmAtomicCommit *commit, const QRect &src, const QRect &dst)
 {
     // Src* are in 16.16 fixed point format
-    commit->addProperty(srcX, srcPos.x() << 16);
-    commit->addProperty(srcX, srcPos.x() << 16);
-    commit->addProperty(srcY, srcPos.y() << 16);
-    commit->addProperty(srcW, srcSize.width() << 16);
-    commit->addProperty(srcH, srcSize.height() << 16);
+    commit->addProperty(srcX, src.x() << 16);
+    commit->addProperty(srcY, src.y() << 16);
+    commit->addProperty(srcW, src.width() << 16);
+    commit->addProperty(srcH, src.height() << 16);
     commit->addProperty(crtcX, dst.x());
     commit->addProperty(crtcY, dst.y());
     commit->addProperty(crtcW, dst.width());

src/backends/drm/drm_plane.h

@@ -41,7 +41,7 @@ public:
     void setCurrentBuffer(const std::shared_ptr<DrmFramebuffer> &b);
     void releaseCurrentBuffer();
 
-    void set(DrmAtomicCommit *commit, const QPoint &srcPos, const QSize &srcSize, const QRect &dst);
+    void set(DrmAtomicCommit *commit, const QRect &src, const QRect &dst);
 
     enum class TypeIndex : uint64_t {
         Overlay = 0,