IViewObject::Draw method (oleidl.h)

Article
10/13/2021

Draws a representation of an object onto the specified device context.

Syntax

HRESULT Draw(
  [in] DWORD                          dwDrawAspect,
  [in] LONG                           lindex,
  [in] void                           *pvAspect,
  [in] DVTARGETDEVICE                 *ptd,
  [in] HDC                            hdcTargetDev,
  [in] HDC                            hdcDraw,
  [in] LPCRECTL                       lprcBounds,
  [in] LPCRECTL                       lprcWBounds,
  [in] BOOL(* )(ULONG_PTR dwContinue) pfnContinue,
  [in] ULONG_PTR                      dwContinue
);

Parameters

[in] dwDrawAspect

Specifies the aspect to be drawn, that is, how the object is to be represented. Representations include content, an icon, a thumbnail, or a printed document. Valid values are taken from the enumerations DVASPECT and DVASPECT2. Note that newer objects and containers that support optimized drawing interfaces support the DVASPECT2 enumeration values. Older objects and containers that do not support optimized drawing interfaces may not support DVASPECT2. Windowless objects allow only DVASPECT_CONTENT, DVASPECT_OPAQUE, and DVASPECT_TRANSPARENT.

[in] lindex

Portion of the object that is of interest for the draw operation. Its interpretation varies depending on the value in the dwAspect parameter. See the DVASPECT enumeration for more information.

[in] pvAspect

Pointer to additional information in a DVASPECTINFO structure that enables drawing optimizations depending on the aspect specified. Note that newer objects and containers that support optimized drawing interfaces support this parameter as well. Older objects and containers that do not support optimized drawing interfaces always specify NULL for this parameter.

[in] ptd

Pointer to the DVTARGETDEVICE structure that describes the device for which the object is to be rendered. If NULL, the view should be rendered for the default target device (typically the display). A value other than NULL is interpreted in conjunction with hdcTargetDev and hdcDraw. For example, if hdcDraw specifies a printer as the device context, the ptd parameter points to a structure describing that printer device. The data may actually be printed if hdcTargetDev is a valid value or it may be displayed in print preview mode if hdcTargetDev is NULL.

[in] hdcTargetDev

Information context for the target device indicated by the ptd parameter from which the object can extract device metrics and test the device's capabilities. If ptd is NULL; the object should ignore the value in the hdcTargetDev parameter.

[in] hdcDraw

Device context on which to draw. For a windowless object, the hdcDraw parameter should be in MM_TEXT mapping mode with its logical coordinates matching the client coordinates of the containing window. For a windowless object, the device context should be in the same state as the one normally passed by a WM_PAINT message.

[in] lprcBounds

Pointer to a RECTL structure specifying the rectangle on hdcDraw and in which the object should be drawn. This parameter controls the positioning and stretching of the object. This parameter should be NULL to draw a windowless in-place active object. In every other situation, NULL is not a legal value and should result in an E_INVALIDARG error code. If the container passes a non-NULL value to a windowless object, the object should render the requested aspect into the specified device context and rectangle. A container can request this from a windowless object to render a second, non-active view of the object or to print the object.

[in] lprcWBounds

If hdcDraw is a metafile device context, pointer to a RECTL structure specifying the bounding rectangle in the underlying metafile. The rectangle structure contains the window extent and window origin. These values are useful for drawing metafiles. The rectangle indicated by lprcBounds is nested inside this lprcWBounds rectangle; they are in the same coordinate space.

If hdcDraw is not a metafile device context; lprcWBounds will be NULL.

[in] pfnContinue

Pointer to a callback function that the view object should call periodically during a lengthy drawing operation to determine whether the operation should continue or be canceled. This function returns TRUE to continue drawing. It returns FALSE to stop the drawing in which case IViewObject::Draw returns DRAW_E_ABORT.

dwContinue

[in] dwContinue

Value to pass as a parameter to the function pointed to by the pfnContinue parameter. Typically, dwContinue is a pointer to an application-defined structure needed inside the callback function.

Return value

This method returns S_OK on success. Other possible return values include the following.

Return code	Description
OLE_E_BLANK	No data to draw from.
DRAW_E_ABORT	Draw operation aborted.
VIEW_E_DRAW	Error in drawing.
DV_E_LINDEX	Invalid value for lindex; currently only -1 is supported.
DV_E_DVASPECT	Invalid value for dwAspect.
OLE_E_INVALIDRECT	Invalid rectangle.

Remarks

A container application issues a call to IViewObject::Draw to create a representation of a contained object. This method draws the specified piece (lindex) of the specified view (dwAspect and pvAspect) on the specified device context (hdcDraw). Formatting, fonts, and other rendering decisions are made on the basis of the target device specified by the ptd parameter.

There is a relationship between the dwDrawAspect value and the lprcbounds value. The lprcbounds value specifies the rectangle on hdcDraw into which the drawing is to be mapped. For DVASPECT_THUMBNAIL, DVASPECT_ICON, and DVASPECT_SMALLICON, the object draws whatever it wants to draw, and it maps it into the space given in the best way. Some objects might scale to fit while some might scale to fit but preserve the aspect ratio. In addition, some might scale so the drawing appears at full width, but the bottom is cropped. The container can suggest a size via IOleObject::SetExtent, but it has no control over the rendering size. In the case of DVASPECT_CONTENT, the IViewObject::Draw implementation should either use the extents given by IOleObject::SetExtent or use the bounding rectangle given in the lprcBounds parameter.

For newer objects that support optimized drawing techniques and for windowless objects, this method should be used as follows:

New drawing aspects are supported in dwAspect as defined in DVASPECT2.
The pvAspect parameter can be used to pass additional information allowing drawing optimizations through the DVASPECTINFO structure.
The IViewObject::Draw method can be called to redraw a windowless in-place active object by setting the lrpcBounds parameter to NULL. In every other situation, NULL is an illegal value and should result in an E_INVALIDARG error code. A windowless object uses the rectangle passed by the activation verb or calls IOleInPlaceObject::SetObjectRects instead of using this parameter. If the container passes a non-NULL value to a windowless object, the object should render the requested aspect into the specified device context and rectangle. A container can request this from a windowless object to render a second, non-active view of the object or to print the object. See the IOleInPlaceSiteWindowless interface for more information on drawing windowless objects.
For windowless objects, the dwAspect parameter only allows the DVASPECT_CONTENT, DVASPECT_OPAQUE, and DVASPECT_TRANSPARENT aspects.
For a windowless object, the hdcDraw parameter should be in MM_TEXT mapping mode with its logical coordinates matching the client coordinates of the containing window. For a windowless object, the device context should be in the same state as the one normally passed by a WM_PAINT message.

To maintain compatibility with older objects and containers that do not support drawing optimizations, all objects, rectangular or not, are required to maintain an origin and a rectangular extent. This allows the container to still consider all its embedded objects as rectangles and to pass them appropriate rendering rectangles in Draw.

An object's extent depends on the drawing aspect. For non-rectangular objects, the extent should be the size of a rectangle covering the entire aspect. By convention, the origin of an object is the top-left corner of the rectangle of the DVASPECT_CONTENT aspect. In other words, the origin always coincides with the top-left corner of the rectangle maintained by the object's site, even for a non-rectangular object.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	oleidl.h

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