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 UI as bitmaps. However, it does not affect applications painting to the off-screen buffers depending on the technologies used for that, it might still be CPU-bound. The DWM uses DirectX 9 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. Under Windows 7 and with WDDM 1.1 drivers, DWM only writes the the program's buffer to the video RAM, even if it is a GDI program, 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. The Desktop Window Manager is a Compositing window manager, each program has a buffer that it writes data to, the DWM then composites each program's buffer into a final image, compared to the stacking window manager in Windows xp and earlier (and Windows 7 and Vista with aero disabled) which has each program writing to the same main buffer.ĭWM works in different ways based on if it is the Windows 7 DWM or the Windows Vista DWM and if the graphics drivers it is using are WDDM 1.0 or 1.1.
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