Greg Schechter, a developer at Microsoft has suggested that this might be opened up for developers and users to plug in their own effects in a future release. With Windows Vista, the transitions are limited to the set of built-in shaders that implement the transformations. Window transitions are implemented as transformations of the meshes, using shader programs. The texture, representing the UI chrome, is then mapped onto these rectangles. The desktop itself is a full-screen Direct3D surface, with windows being represented as a mesh consisting of two adjacent (and mutually-inverted) triangles, which are transformed to represent a 2D rectangle. The window contents in the buffers are then converted to DirectX textures. DWM-aware rendering technologies like WPF directly make the internal data structures available in a DWM-compatible format. DWM-agnostic rendering techniques like GDI are redirected to the buffers by rendering the user interface (UI) as bitmaps. However, it does not affect applications painting to the off-screen buffers – depending on the technologies used for that, this might still be CPU-bound. DWM uses DirectX to perform the function of compositing and rendering in the GPU, freeing the CPU of the task of managing the rendering from the off-screen buffers to the display. This is because Windows 7 supports (limited) hardware acceleration for GDI and in doing so does not need to keep a copy of the buffer in system RAM so that the CPU can write to it.īecause the compositor has access to the graphics of all applications, it easily allows visual effects that string together visuals from multiple applications, such as transparency. Under Windows 7 and with WDDM 1.1 drivers, DWM only writes the program's buffer to the video RAM, even if it is a graphics device interface (GDI) program.
By comparison, the stacking window manager in Windows XP and earlier (and also Windows Vista and Windows 7 with Windows Aero disabled) comprises a single display buffer to which all programs write.ĭWM works in different ways depending on the operating system (Windows 7 or Windows Vista) and on the version of the graphics drivers it uses ( WDDM 1.0 or 1.1). This means that each program has a buffer that it writes data to DWM then composites each program's buffer into a final image.
The Desktop Window Manager is a compositing window manager.
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