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图像放大e Viewer Rendering

The图像放大eViewerrendering cycle supports full customization. The various events and their data allow for any of the following:

Add user-defined rendering code on the view or the items. For example, the LEADTOOLS annotations framework hooks to the rendering cycle to draw the annotations container on top of an item.
Perform full owner drawing of any part of the view or item. For example, the图像放大eViewerVirtualizerhooks to the render event to draw a place holder when the image data is not present yet.
Re-direct the rendering to an external context. For example, the图像放大eViewerPanControluses redirection to duplicate the current appearance of the viewer to an external control.

Rendering Cycle

The rendering cycle occurs when图像放大eViewer.Invalidateor图像放大eViewer.RenderRedirectis called due to normal control painting or a response to图像放大eViewer.UpdateTransform. To customize the rendering cycle, you can either subscribe to the specific event or derive from the图像放大eViewerand override the specific virtual method. All these methods and event use the图像放大eViewerRenderEventArgsclass to hold the information needed.

图像放大eViewerRenderEventArgscontains the following:

Member	Description
Context	In Windows Forms, the`System.Drawing.Graphics`object of the viewer control during paint or that of the target device duringRenderRedirect. In JavaScript, the HTML`CanvasContext2D`object for the fore canvas or that of the target device duringRenderRedirect.
PaintEventArgs	Original Windows.Forms paint arguments if this render event is in response to`System.Windows.Forms.Control.Paint`.
Item	The item being rendered or null of this part of the rendering cycle is view-specific.
Part	The item part being rendered or View if this part of the rendering cycle is is view-specific.
错误	An error that was caught during the rendering cycle. Used with the图像放大eViewer.RenderErrorevent.
ImageViewerRenderEventArgs。ClipRectangle	Current clipping rectangle to be applied.

The image viewer will call the virtual methods and fires the events in the order described below. Note for members,ImageViewerRenderEventArgs。Contexwill point to theSystem.Drawing.Graphics(in Windows.Forms) or (HTMLCanvasContext2Dobject for the fore canvas in JavaScript) the viewer control or the redirect target.

Method - Event	ImageViewerRenderEventArgs。Item,Part	Default Operations
`图像放大eViewer.OnEraseBackground`-`图像放大eViewer.EraseBackground`JavaScript only	null-图像放大eViewerItem.View	Erases or clears the background
OnPreRender-PreRender	null-图像放大eViewerItem.View	Nothing. Can be used to set the context properties (for example, anti-aliasing or interpolation quality)
OnRenderShadow-RenderShadow	null-图像放大eViewerItem.View	Renders the drop shadow of the view
OnRenderBorder-RenderBorder	null-图像放大eViewerItem.View	Renders the border of the view
For each item		Loops through the items in the viewer. Only occur if the item isIsVisible, has none empty图像放大eSizeand if it intersects with the current visible viewer surface and clipping rectangle.
OnPreRenderItem-PreRenderItem	The item - Item	Nothing
OnRenderItem-RenderItem	The item - Item	Nothing
OnRenderBackground-RenderBackground	The item - Item	Fills the content of the item with the background color based on the item state
OnRenderBorder-RenderBorder	The item - Content	Renders the content border using the border color based on the item state
OnRenderShadow-RenderShadow	The item - Image	Renders the drop shadow around the image of the item
OnRenderImage-RenderImage	The item - Image	Renders the item image
OnRenderBorder-RenderBorder	The item - Image	Renders the border of the image
OnRenderText-RenderText	The item - Text	Renders the text of the item
OnPostRenderItem-PostRenderItem	The item - Item	Nothing
Next item
OnPostRender-PostRender	null-图像放大eViewerItem.View	Renders the floaters and regions
OnRedirectRender-RedirectRender	null-图像放大eViewerItem.View	Nothing

The most common custom rendering is performed by subscribing to these events:

PostRenderItem: To render extra information on top of an item
PostRender: To render extra information on top of the whole viewer

Refer to these events for an example.

To manually trigger a new rendering cycle, call图像放大eViewer.Invalidateto invalidate a portion of the whole surface of the viewer. This method accepts a rectangle that specifies the portion of the viewer to update for optimal speed. TheInvalidateItemorInvalidateItemByIndexmethods can be used to re-render a single item quickly.

错误s when Rendering

Rendering of the图像放大eViewercontrol normally occurs automatically and not through any code called by the user. If an error occur, the user does not have the ability to try/catch the exception and process the error. Therefore,图像放大eViewercontains theRenderErrorevents. This will occur when an error happens in the internal rendering cycle. The event uses the same图像放大eViewerRenderEventArgsdata class, so all the usual parameters of what item and part caused the error are passed to the user. In addition, it will catch the error and set it in theImageViewerRenderEventArgs。错误property.

Other Rendering Operations

The ImageViewer also supports the following operations related to rendering:

Display

Member	Description
Invert	Display all items with inverted colors
ScreenDpi	Update the value of the screen resolution in dots per inch
UseDpi	Account for the resolution of the image in the items when calculating the display size
AspectRatioCorrection	Manually change the aspect ratio used to compensate for non-square pixels
BeginRender	Temporally disable rendering
EndRender	Re-enable rendering
图像放大eViewer.Invalidate	Request that the viewer re-renders the whole or part of the view
PaintProperties	Controls the quality used when rendering RasterImage objects
RedirectRender	Render the current view to an external context
ClipImageToContent	Display only the part of the image inside its content if the item transformation result in a larger boundary
OwnerDraw	Turn off or on all automatic rendering of view and items