Supporting Rotation in a Display Miniport Driver
A display miniport driver's DxgkDdiEnumVidPnCofuncModality function calls the pfnUpdatePathSupportInfo function to report rotation support for each path in a video present network (VidPN) topology. For more information about reporting rotation support, see Enumerating Cofunctional VidPN Source and Target Modes.
The Microsoft DirectX graphics kernel subsystem uses non-rotated surface dimensions to create the shared primary surface. To notify a display miniport driver to rotate the surface, the DirectX graphics kernel subsystem specifies D3DKMDT_VIDPN_PRESENT_PATH_ROTATION-typed values in the Rotation member of the D3DKMDT_VIDPN_PRESENT_PATH_TRANSFORMATION structure that is specified in the ContentTransformation member of the D3DKMDT_VIDPN_PRESENT_PATH structure in calls to the display miniport driver's DxgkDdiCommitVidPn and DxgkDdiUpdateActiveVidPnPresentPath functions.
Note All rotation degrees are defined in the counter-clockwise direction, which is consistent with how GDI defines rotation.
When the DirectX subsystem notifies the display miniport driver to rotate the surface, the driver should rotate the surface data only if the Rotate bit-field flag was set in the Flags member of the DXGKARG_PRESENT structure that the pPresent parameter points to in a call to the driver's DxgkDdiPresent function. Even if the driver determines that the current orientation of the screen is rotated from the presentation data and Rotate was not set, the driver should not rotate the data.
Clone-mode behavior
Clone mode is a mode in which a video present source connects to multiple video present targets through multiple paths in a video present network. (For more information about video present networks, see Multiple Monitors and Video Present Networks.)
A display miniport driver handles rotation differently if it operates in clone mode because each target might require a different rotation. The operating system, various versions of Microsoft DirectX runtimes, and user-mode clients detect only the orientation of the primary video present target. Therefore, the content in the video present source will always match the orientation of the primary video present target.
The following table shows how a display miniport driver behaves in clone mode for all of the relevant situations. The setting of the Rotate flag is the setting of the Rotate bit-field in the Flags member of the DXGKARG_PRESENT structure.
| Primary target | Secondary target | Rotate flag | Driver behavior |
|---|---|---|---|
Not rotated |
Not rotated |
Not set |
The driver performs no rotation. |
Not rotated |
Rotated |
Not set |
The driver rotates the secondary target even though the Rotate flag is not set. |
Rotated |
Not rotated |
Set |
The driver rotates the primary target but not the secondary target. |
Rotated |
Not rotated |
Not set |
Because Rotate is not set, the driver does not rotate the primary target. Because the secondary target does not match the orientation of the content in the source, the driver must rotate the secondary target. This situation occurs when the client is rotation-aware, and it already has properly oriented the content of the source. Therefore, the operating system does not set Rotate. |
Rotated |
Rotated |
Set |
The driver rotates both the primary and secondary targets. |
Rotated |
Rotated |
Not set |
The rotation-aware client has already properly oriented the content of the source. Therefore, no additional rotation is required. |
Clone-mode requirements starting with Windows 8.1 Update
Starting with Windows 8.1 Update, drivers must meet these requirements. If test signing is enabled, a system bugcheck will occur if a driver fails to meet these requirements.
Primary clone path
Definition: The path that includes the target monitor that duplicates the source display—for example, an external monitor that duplicates the display on a laptop computer.
Requirement: In the primary clone path, the driver must set Offset0 to TRUE and the other 3 offset values in D3DKMDT_VIDPN_PRESENT_PATH_ROTATION_SUPPORT to FALSE.
In the case of a portrait-first source display, the primary clone path is not rotationally offset. This means that the primary clone path always has an offset of zero (D3DKMDT_VIDPN_PRESENT_PATH_ROTATION_SUPPORT.Offset0 is TRUE), and the Desktop Window Manager (DWM) rotates its content in advance to match the proper orientation.
The primary clone path determines the monitor refresh rate for all primary and secondary clone targets.
Secondary clone path
Definition: The path that includes any additional target monitor, not part of the primary clone path, that also duplicates the source display.
Requirement: In the secondary clone path, the driver must set at least one of the 4 offset values in D3DKMDT_VIDPN_PRESENT_PATH_ROTATION_SUPPORT to TRUE. If the driver doesn't support path-independent rotation, it should set Offset0 to TRUE in all secondary clone paths.
Here are two examples of settings the driver should make if it supports path-independent rotation:
Landscape-first example
If the source display and the target in the secondary clone path are both landscape-first monitors, in the secondary clone path the driver would set D3DKMDT_VIDPN_PRESENT_PATH_ROTATION_SUPPORT.Offset0 to TRUE and the other 3 offset values in D3DKMDT_VIDPN_PRESENT_PATH_ROTATION_SUPPORT to FALSE. Alternately in this case, in the secondary clone path the driver would set both Offset0 and Offset180 to TRUE and the other offset values to FALSE.
Portrait-first example
If the source display is a portrait-first device and connects to a landscape-first external monitor, in the secondary clone path the driver would set either Offset270 or Offset90 to TRUE.
For more info, see Supporting Path-Independent Rotation.