renderRedirect Method

Summary

Renders the content of the viewer to an external context.

Syntax
TypeScript
JavaScript
ImageViewer.prototype.renderRedirect = function( 
   context, 
   options, 
   clipRectangle 
) 
renderRedirect( 
   context: CanvasRenderingContext2D, 
   options: ImageViewerRenderRedirectOptions, 
   clipRectangle: LeadRectD 
): void; 

Parameters

context

Target HTML5 Canvas Element context to render the content of the viewer to.

options

Rendering options

clipRectangle

Clipping rectangle to use.

Remarks

This method can be used to render the content of the viewer to an external context. ImageViewerPanControl uses this method to show a smaller version of the viewer in a separate external control.

To take a "snapshot" of the viewer surface to perform such operations as screen capture or printing, use RenderRedirect passing it the target context (of the printer or a bitmap).

To perform live updates for operations such as pan window, subscribe to the RedirectRender event to get notified whenever the viewer content is changed. Then call RenderRedirect to render the content of the viewer into the target device.

During the render cycle, the value of IsRenderRedirected will be set to true if this particular rendering operation is targeting an external device other than the viewer itself. If you are performing custom rendering, you can check the value of this property to apply any modification needed.

Example

This example will mirror the content of the viewer into an external canvas with live updates whenever the viewer content changes.

RenderRedirect.ts
ImageViewer.ts
RenderRedirect.js
ImageViewer.js
RenderRedirect.html
import { ImageViewer_Example } from "../ImageViewer"; 
 
export class ImageViewer_RenderRedirectExample { 
   private viewerExample; 
   constructor() { 
      this.viewerExample = new ImageViewer_Example(this.run); 
   } 
 
   private run = (viewer: lt.Controls.ImageViewer) => { 
      viewer.itemBorderThickness = 5; 
 
      // Create the canvas we will render to 
      const redirectCanvas = document.createElement("canvas"); 
      redirectCanvas.style.border = "2px solid black"; 
      const redirectWidth: number = 300; 
      const redirectHeight: number = 300; 
      redirectCanvas.width = redirectWidth; 
      redirectCanvas.height = redirectHeight; 
 
      // Add it to the page 
      const output = document.getElementById("output"); 
      output.appendChild(redirectCanvas); 
 
      // Add a 20px margin around the redirect render area 
      const delta: number = 20; 
      const destRect: lt.LeadRectD = lt.LeadRectD.create(0, 0, redirectWidth, redirectHeight); 
      destRect.inflate(-delta, -delta); 
 
      const options: lt.Controls.ImageViewerRenderRedirectOptions = new lt.Controls.ImageViewerRenderRedirectOptions(); 
 
      viewer.rotateAngle = 35; 
      // Use "null" to draw the whole imageViewer 
      //let item = null; 
      const item: lt.Controls.ImageViewerItem = viewer.activeItem; 
 
      if (item) { 
         // Don't worry about rendering the below 
         options.renderBackgrounds = false; 
         options.renderBorders = false; 
         options.renderItemStates = false; 
         options.renderShadows = false; 
         options.renderText = false; 
      } 
 
      // On imageViewer render... 
      viewer.redirectRender.add(() => { 
         let sourceRect: lt.LeadRectD; 
         let sourceRectClipped: lt.LeadRectD; 
         if (!item) { 
            // Draw the whole imageViewer 
            sourceRect = viewer.getViewBounds(true, false); 
            sourceRectClipped = viewer.getViewBounds(true, true); 
         } 
         else { 
            // Only draw the rect for the active item 
            sourceRect = viewer.getItemViewBounds(item, lt.Controls.ImageViewerItemPart.image, false); 
            sourceRectClipped = viewer.getItemViewBounds(item, lt.Controls.ImageViewerItemPart.image, true); 
         } 
 
         const ctx: CanvasRenderingContext2D = redirectCanvas.getContext("2d"); 
         ctx.clearRect(0, 0, redirectWidth, redirectHeight); 
 
         // Draw a rect around the maximum render area 
         ctx.strokeStyle = "green"; 
         ctx.strokeRect(destRect.x, destRect.y, destRect.width, destRect.height); 
 
         // Create the transformation for this rect 
         options.createTransform(viewer, destRect, sourceRect, lt.Controls.ControlSizeMode.fit, lt.Controls.ControlAlignment.center, lt.Controls.ControlAlignment.center); 
 
         // Draw a rect around the actual render area 
         const clipRect: lt.LeadRectD = options.transform.transformRect(sourceRect); 
         ctx.strokeStyle = "orange"; 
         ctx.strokeRect(clipRect.x, clipRect.y, clipRect.width, clipRect.height); 
 
         // Do the redirect render 
         viewer.renderRedirect(ctx, options, lt.LeadRectD.empty); 
 
         // Show how to draw the item's border 
         const manuallyComputeRedirectedBorder = () => { 
            const points: lt.LeadPointD[] = [lt.LeadPointD.create(sourceRectClipped.left, sourceRectClipped.top), lt.LeadPointD.create(sourceRectClipped.right, sourceRectClipped.bottom)]; 
            options.transform.transformPoints(points); 
 
            let xmin = points[0].x; 
            let ymin = points[0].y; 
            let xmax = xmin; 
            let ymax = ymin; 
 
            for (let i = 1; i < points.length; i++) { 
               if (points[i].x < xmin) xmin = points[i].x; 
               if (points[i].x > xmax) xmax = points[i].x; 
               if (points[i].y < ymin) ymin = points[i].y; 
               if (points[i].y > ymax) ymax = points[i].y; 
            } 
 
            const bounds: lt.LeadRectD = lt.LeadRectD.fromLTRB(xmin, ymin, xmax, ymax); 
 
            ctx.strokeStyle = "blue"; 
            ctx.strokeRect(bounds.x, bounds.y, bounds.width, bounds.height); 
         }; 
         manuallyComputeRedirectedBorder(); 
      }); 
      viewer.invalidate(lt.LeadRectD.empty); 
   } 
} 
export class ImageViewer_Example { 
   // LEADTOOLS ImageViewer to be used with this example 
   protected imageViewer: lt.Controls.ImageViewer = null; 
   // Generic state value used by the examples 
   public timesClicked: number = 0; 
 
   constructor(callback?: (viewer: lt.Controls.ImageViewer) => void) { 
      // Set the LEADTOOLS license. Replace this with your actual license file 
      lt.RasterSupport.setLicenseUri("https://demo.leadtools.com/licenses/js/LEADTOOLSEVAL.txt", "EVAL", null); 
 
      // Create an image viewer inside the imageViewerDiv element 
      const imageViewerDiv = document.getElementById("imageViewerDiv"); 
      const createOptions: lt.Controls.ImageViewerCreateOptions = new lt.Controls.ImageViewerCreateOptions(imageViewerDiv); 
      this.imageViewer = new lt.Controls.ImageViewer(createOptions); 
      this.imageViewer.viewVerticalAlignment = lt.Controls.ControlAlignment.center; 
      this.imageViewer.viewHorizontalAlignment = lt.Controls.ControlAlignment.center; 
      this.imageViewer.autoCreateCanvas = true; 
 
      // Add Pan/Zoom interactive mode 
      // Click and drag to pan, CTRL-Click and drag to zoom in and out 
      this.imageViewer.interactiveModes.add(new lt.Controls.ImageViewerPanZoomInteractiveMode()); 
 
      // Load an image 
      this.imageViewer.imageUrl = "https://demo.leadtools.com/images/jpeg/cannon.jpg"; 
 
      this.imageViewer.zoom(lt.Controls.ControlSizeMode.fit, .9, this.imageViewer.defaultZoomOrigin); 
 
      const exampleButton = document.getElementById("exampleButton"); 
      exampleButton.addEventListener("click", () => { 
         this.timesClicked++; 
         // Run the example 
         if (callback) 
            callback(this.imageViewer); 
      }); 
   } 
} 
import { ImageViewer_Example } from "../ImageViewer"; 
 
export class ImageViewer_RenderRedirectExample { 
   viewerExample; 
   constructor() { 
      this.viewerExample = new ImageViewer_Example(this.run); 
   } 
 
   run = (viewer) => { 
      viewer.itemBorderThickness = 5; 
 
      // Create the canvas we will render to 
      const redirectCanvas = document.createElement("canvas"); 
      redirectCanvas.style.border = "2px solid black"; 
      const redirectWidth = 300; 
      const redirectHeight = 300; 
      redirectCanvas.width = redirectWidth; 
      redirectCanvas.height = redirectHeight; 
 
      // Add it to the page 
      const output = document.getElementById("output"); 
      output.appendChild(redirectCanvas); 
 
      // Add a 20px margin around the redirect render area 
      const delta = 20; 
      const destRect = lt.LeadRectD.create(0, 0, redirectWidth, redirectHeight); 
      destRect.inflate(-delta, -delta); 
 
      const options = new lt.Controls.ImageViewerRenderRedirectOptions(); 
 
      viewer.rotateAngle = 35; 
      // Use "null" to draw the whole imageViewer 
      //let item = null; 
      const item = viewer.activeItem; 
 
      if (item) { 
         // Don't worry about rendering the below 
         options.renderBackgrounds = false; 
         options.renderBorders = false; 
         options.renderItemStates = false; 
         options.renderShadows = false; 
         options.renderText = false; 
      } 
 
      // On imageViewer render... 
      viewer.redirectRender.add(() => { 
         let sourceRect; 
         let sourceRectClipped; 
         if (!item) { 
            // Draw the whole imageViewer 
            sourceRect = viewer.getViewBounds(true, false); 
            sourceRectClipped = viewer.getViewBounds(true, true); 
         } 
         else { 
            // Only draw the rect for the active item 
            sourceRect = viewer.getItemViewBounds(item, lt.Controls.ImageViewerItemPart.image, false); 
            sourceRectClipped = viewer.getItemViewBounds(item, lt.Controls.ImageViewerItemPart.image, true); 
         } 
 
         const ctx = redirectCanvas.getContext("2d"); 
         ctx.clearRect(0, 0, redirectWidth, redirectHeight); 
 
         // Draw a rect around the maximum render area 
         ctx.strokeStyle = "green"; 
         ctx.strokeRect(destRect.x, destRect.y, destRect.width, destRect.height); 
 
         // Create the transformation for this rect 
         options.createTransform(viewer, destRect, sourceRect, lt.Controls.ControlSizeMode.fit, lt.Controls.ControlAlignment.center, lt.Controls.ControlAlignment.center); 
 
         // Draw a rect around the actual render area 
         const clipRect = options.transform.transformRect(sourceRect); 
         ctx.strokeStyle = "orange"; 
         ctx.strokeRect(clipRect.x, clipRect.y, clipRect.width, clipRect.height); 
 
         // Do the redirect render 
         viewer.renderRedirect(ctx, options, lt.LeadRectD.empty); 
 
         // Show how to draw the item's border 
         const manuallyComputeRedirectedBorder = () => { 
            const points = [lt.LeadPointD.create(sourceRectClipped.left, sourceRectClipped.top), lt.LeadPointD.create(sourceRectClipped.right, sourceRectClipped.bottom)]; 
            options.transform.transformPoints(points); 
 
            let xmin = points[0].x; 
            let ymin = points[0].y; 
            let xmax = xmin; 
            let ymax = ymin; 
 
            for (let i = 1; i < points.length; i++) { 
               if (points[i].x < xmin) xmin = points[i].x; 
               if (points[i].x > xmax) xmax = points[i].x; 
               if (points[i].y < ymin) ymin = points[i].y; 
               if (points[i].y > ymax) ymax = points[i].y; 
            } 
 
            const bounds = lt.LeadRectD.fromLTRB(xmin, ymin, xmax, ymax); 
 
            ctx.strokeStyle = "blue"; 
            ctx.strokeRect(bounds.x, bounds.y, bounds.width, bounds.height); 
         }; 
         manuallyComputeRedirectedBorder(); 
      }); 
      viewer.invalidate(lt.LeadRectD.empty); 
   } 
} 
export class ImageViewer_Example { 
   // LEADTOOLS ImageViewer to be used with this example 
   imageViewer = null; 
   // Generic state value used by the examples 
   timesClicked = 0; 
 
   constructor(callback) { 
      // Set the LEADTOOLS license. Replace this with your actual license file 
      lt.RasterSupport.setLicenseUri("https://demo.leadtools.com/licenses/js/LEADTOOLSEVAL.txt", "EVAL", null); 
 
      // Create an image viewer inside the imageViewerDiv element 
      const imageViewerDiv = document.getElementById("imageViewerDiv"); 
      const createOptions = new lt.Controls.ImageViewerCreateOptions(imageViewerDiv); 
      this.imageViewer = new lt.Controls.ImageViewer(createOptions); 
      this.imageViewer.viewVerticalAlignment = lt.Controls.ControlAlignment.center; 
      this.imageViewer.viewHorizontalAlignment = lt.Controls.ControlAlignment.center; 
      this.imageViewer.autoCreateCanvas = true; 
 
      // Add Pan/Zoom interactive mode 
      // Click and drag to pan, CTRL-Click and drag to zoom in and out 
      this.imageViewer.interactiveModes.add(new lt.Controls.ImageViewerPanZoomInteractiveMode()); 
 
      // Load an image 
      this.imageViewer.imageUrl = "https://demo.leadtools.com/images/jpeg/cannon.jpg"; 
 
      this.imageViewer.zoom(lt.Controls.ControlSizeMode.fit, .9, this.imageViewer.defaultZoomOrigin); 
 
      const exampleButton = document.getElementById("exampleButton"); 
      exampleButton.addEventListener("click", () => { 
         this.timesClicked++; 
         // Run the example 
         if (callback) 
            callback(this.imageViewer); 
      }); 
   } 
} 
<!doctype html> 
<html lang="en"> 
<title>Controls Example | RenderRedirect</title> 
 
<head> 
   <script src="https://code.jquery.com/jquery-2.2.4.min.js" 
      integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44=" crossorigin="anonymous"></script> 
 
   <script src="../../LT/Leadtools.js"></script> 
   <script src="../../LT/Leadtools.Controls.js"></script> 
   <script src="../../LT/Leadtools.Annotations.Engine.js"></script> 
   <script src="../../LT/Leadtools.Annotations.Designers.js"></script> 
   <script src="../../LT/Leadtools.Annotations.Rendering.Javascript.js"></script> 
   <script src="../../LT/Leadtools.Annotations.Automation.js"></script> 
   <script src="../../LT/Leadtools.ImageProcessing.Main.js"></script> 
   <script src="../../LT/Leadtools.ImageProcessing.Color.js"></script> 
   <script src="../../LT/Leadtools.ImageProcessing.Core.js"></script> 
   <script src="../../LT/Leadtools.ImageProcessing.Effects.js"></script> 
   <script src="../../LT/Leadtools.Document.js"></script> 
   <script src="../../LT/Leadtools.Document.Viewer.js"></script> 
   <style> 
      body { 
         font-family: 'Segoe UI', sans-serif; 
      } 
 
      #imageViewerDiv { 
         border: 1px solid #888; 
         width: 500px; 
         height: 500px; 
         background-color: #eee; 
      } 
   </style> 
 
   <!-- All demo files are bundled and appended to the window --> 
   <script src="../../bundle.js" type="text/javascript"></script> 
</head> 
 
<body> 
   <p>Press and drag on the image to pan.</p> 
   <p>Hold down the control key and press and drag on the image or pinch with two fingers to zoom in and out.</p> 
   <div> 
      <button type="button" id="exampleButton">Run Example</button> 
   </div> 
   <div id="imageViewerDiv"></div> 
   <div id="output"></div> 
</body> 
 
<script> 
   window.onload = () => { 
      const example = new window.examples.ImageViewer.RenderRedirect(); 
 
   }; 
</script> 
</html> 
Requirements

Target Platforms

Help Version 22.0.2021.9.24
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© 1991-2021 LEAD Technologies, Inc. All Rights Reserved.

Leadtools.Controls Assembly
Products | Support | Contact Us | Intellectual Property Notices
© 1991-2021 LEAD Technologies, Inc. All Rights Reserved.