MagSetImageScalingCallback function (magnification.h)

Sets the callback function for external image filtering and scaling.

Syntax

BOOL MagSetImageScalingCallback(
  [in] HWND                    hwnd,
  [in] MagImageScalingCallback callback
);

Parameters

[in] hwnd

Type: HWND

The handle of the magnification window.

[in] callback

Type: MagImageScalingCallback

The callback function, or NULL to remove a callback that was previously set.

Return value

Type: BOOL

Returns TRUE if successful, or FALSE otherwise.

Remarks

This function requires Windows Display Driver Model (WDDM)-capable video cards.

This function works only when Desktop Window Manager (DWM) is off.

This callback mechanism enables custom image filtering and scaling mechanisms. Filtering might include bilinear, trilinear, bicubic, and flat. The mechanism also enables edge detection and enhancement.

The only transform that can be performed within the callback is scaling. Rotations and skews that may compose the arbitrary transform passed to the MagSetWindowTransform function are performed after the callback function returns.

The specified function is called by the magnification engine for all rasterized Windows Graphics Device Interface (GDI) bitmaps before they are composited.

After the callback function returns, the bitmap in video memory can have one of the following size states:

• Unscaled. The returned bitmap is the same size as the bitmap passed by the caller. The magnification engine does the scaling by the transform specified in the MagSetWindowTransform function.
• Scaled. The returned bitmap is scaled by the transform specified in MagSetWindowTransform.

If no callback is registered, the magnification engine scales bitmaps by the transform specified in MagSetWindowTransform.

Windows Presentation Foundation (WPF) bitmaps can be scaled automatically using flat, bilinear, bicubic filtering and consequently do not use this callback mechanism.

Requirements

Requirement	Value
Minimum supported client	Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2008 [desktop apps only]
Target Platform	Windows
Header	magnification.h
Library	Magnification.lib
DLL	Magnification.dll

See also

MagGetImageScalingCallback

MagSetImageScalingCallback