core: Introduce GraphicsBufferView

GraphicsBufferView provides a way to map the contents of a graphics
buffer as an image.

src/CMakeLists.txt

@@ -42,6 +42,7 @@ target_sources(kwin PRIVATE
     core/gbmgraphicsbufferallocator.cpp
     core/graphicsbuffer.cpp
     core/graphicsbufferallocator.cpp
+    core/graphicsbufferview.cpp
     core/inputbackend.cpp
     core/inputdevice.cpp
     core/output.cpp

src/core/graphicsbuffer.cpp

@@ -53,6 +53,15 @@ void GraphicsBuffer::drop()
     }
 }
 
+void *GraphicsBuffer::map()
+{
+    return nullptr;
+}
+
+void GraphicsBuffer::unmap()
+{
+}
+
 const DmaBufAttributes *GraphicsBuffer::dmabufAttributes() const
 {
     return nullptr;

src/core/graphicsbuffer.h

@@ -58,6 +58,9 @@ public:
     void unref();
     void drop();
 
+    virtual void *map();
+    virtual void unmap();
+
     virtual QSize size() const = 0;
     virtual bool hasAlphaChannel() const = 0;
 

src/core/graphicsbufferview.cpp

@@ -0,0 +1,91 @@
+/*
+    SPDX-FileCopyrightText: 2023 Vlad Zahorodnii <vlad.zahorodnii@kde.org>
+
+    SPDX-License-Identifier: GPL-2.0-or-later
+*/
+
+#include "core/graphicsbufferview.h"
+#include "core/graphicsbuffer.h"
+#include "utils/common.h"
+
+#include <drm_fourcc.h>
+
+namespace KWin
+{
+
+static QImage::Format drmFormatToQImageFormat(uint32_t drmFormat)
+{
+    switch (drmFormat) {
+#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
+    case DRM_FORMAT_ABGR16161616:
+        return QImage::Format_RGBA64_Premultiplied;
+    case DRM_FORMAT_XBGR16161616:
+        return QImage::Format_RGBX64;
+    case DRM_FORMAT_ARGB2101010:
+        return QImage::Format_A2RGB30_Premultiplied;
+    case DRM_FORMAT_XRGB2101010:
+        return QImage::Format_RGB30;
+    case DRM_FORMAT_ABGR2101010:
+        return QImage::Format_A2BGR30_Premultiplied;
+    case DRM_FORMAT_XBGR2101010:
+        return QImage::Format_BGR30;
+#endif
+    case DRM_FORMAT_ARGB8888:
+        return QImage::Format_ARGB32_Premultiplied;
+    case DRM_FORMAT_XRGB8888:
+        return QImage::Format_RGB32;
+    default:
+        return QImage::Format_Invalid;
+    }
+}
+
+GraphicsBufferView::GraphicsBufferView(GraphicsBuffer *buffer)
+    : m_buffer(buffer)
+{
+    int width;
+    int height;
+    int stride;
+    int format;
+
+    if (auto dmabuf = buffer->dmabufAttributes()) {
+        if (dmabuf->planeCount != 1) {
+            return;
+        }
+        width = dmabuf->width;
+        height = dmabuf->height;
+        stride = dmabuf->pitch[0];
+        format = dmabuf->format;
+    } else if (auto shm = buffer->shmAttributes()) {
+        width = shm->size.width();
+        height = shm->size.height();
+        stride = shm->stride;
+        format = shm->format;
+    } else {
+        qCWarning(KWIN_CORE) << "Cannot create a graphics buffer view for unknown buffer type" << buffer;
+        return;
+    }
+
+    void *data = buffer->map();
+    if (data) {
+        m_image = QImage(static_cast<uchar *>(data), width, height, stride, drmFormatToQImageFormat(format));
+    }
+}
+
+GraphicsBufferView::~GraphicsBufferView()
+{
+    if (!m_image.isNull()) {
+        m_buffer->unmap();
+    }
+}
+
+QImage *GraphicsBufferView::image()
+{
+    return &m_image;
+}
+
+const QImage *GraphicsBufferView::image() const
+{
+    return &m_image;
+}
+
+} // namespace KWin

src/core/graphicsbufferview.h

@@ -0,0 +1,32 @@
+/*
+    SPDX-FileCopyrightText: 2023 Vlad Zahorodnii <vlad.zahorodnii@kde.org>
+
+    SPDX-License-Identifier: GPL-2.0-or-later
+*/
+
+#pragma once
+
+#include "kwin_export.h"
+
+#include <QImage>
+
+namespace KWin
+{
+
+class GraphicsBuffer;
+
+class KWIN_EXPORT GraphicsBufferView
+{
+public:
+    explicit GraphicsBufferView(GraphicsBuffer *buffer);
+    ~GraphicsBufferView();
+
+    QImage *image();
+    const QImage *image() const;
+
+private:
+    GraphicsBuffer *m_buffer;
+    QImage m_image;
+};
+
+} // namespace KWin