redirectCanvas Property

Summary

External HTML5 Canvas Element that can be used to re-direct the spy glass render.

Syntax
TypeScript
JavaScript
Object.defineProperty(ImageViewerSpyGlassInteractiveMode.prototype, 'redirectCanvas', 
	get: function(), 
	set: function(value) 
) 
redirectCanvas: HTMLCanvasElement; 

Property Value

The external canvas that can be used to re-direct the spy glass render. The default value is null.

Remarks

ImageViewerSpyGlassInteractiveMode supports redirecting the render output to an external canvas instead of the area under the mouse in the viewer. When this value is set to a valid canvas on the page, the interactive mode will use this canvas as the target for the spy glass rendering instead of creating an internal instance and rendering the glass over the image viewer.

Example

This example adds a new canvas that the magnify glass will draw to. When dragging, the magnify glass will draw the contents of the viewer with additional text over it.

RedirectCanvas.ts
ImageViewer.ts
RedirectCanvas.js
ImageViewer.js
RedirectCanvas.html
import { ImageViewer_Example } from "../ImageViewer"; 
 
export class SpyGlassInteractiveMode_RedirectCanvasExample { 
   private viewerExample; 
   constructor() { 
      this.viewerExample = new ImageViewer_Example(this.run); 
   } 
 
   private run = (viewer: lt.Controls.ImageViewer) => { 
      const output = document.getElementById("output"); 
 
      // The width and height of our redirect canvas 
      const canvasWidth: number = 250; 
      const canvasHeight: number = 250; 
 
      // Create the redirect canvas 
      const redirectCanvas = document.createElement("canvas") as HTMLCanvasElement; 
      redirectCanvas.style.border = "1px solid black"; 
      redirectCanvas.width = canvasWidth; 
      redirectCanvas.height = canvasHeight; 
 
      // Create the SpyGlass mode 
      const mode: lt.Controls.ImageViewerSpyGlassInteractiveMode = new lt.Controls.ImageViewerSpyGlassInteractiveMode(); 
      mode.workCompleted.add((sender, e) => { 
         if (mode.redirectCanvas) { 
            // Clear after drawing on redirected canvas 
            const ctx: CanvasRenderingContext2D = mode.redirectCanvas.getContext("2d"); 
            ctx.clearRect(0, 0, mode.redirectCanvas.width, mode.redirectCanvas.height) 
         } 
      }); 
      mode.size = lt.LeadSizeD.create(canvasWidth, canvasHeight); 
      mode.redirectCanvas = redirectCanvas; 
      mode.backgroundColor = "yellow"; 
      mode.crosshairColor = "red"; 
 
      mode.drawImage.add((sender, e) => { 
         const rect: lt.LeadRectD = e.destinationRectangle; 
         const ctx: CanvasRenderingContext2D = e.context; 
 
         ctx.save(); 
 
         // Undo offset of the spyglass 
         ctx.translate(-rect.x, -rect.y); 
 
         // We could do anything here. For example, ImageViewerMagnifyGlassInteractiveMode zooms in. 
         // We will draw additional text over the image. 
 
         // Clip to the ImageViewer (optional) 
         const bounds: lt.LeadRectD = viewer.getViewBounds(false, true); 
         ctx.beginPath(); 
         ctx.rect(bounds.x, bounds.y, bounds.width, bounds.height); 
         ctx.closePath(); 
         ctx.clip(); 
 
         // Draw the view 
         viewer.renderRedirect(ctx, new lt.Controls.ImageViewerRenderRedirectOptions(), lt.LeadRectD.empty); 
 
         // Draw some text on top 
         ctx.fillStyle = "white"; 
         ctx.strokeStyle = "white"; 
         ctx.font = "75px Times New Roman"; 
         ctx.fillText("Spyglass", bounds.x + (bounds.width / 2) - 100, bounds.y + (bounds.height / 2)); 
 
         ctx.restore(); 
      }); 
 
      // Add a toggle button 
      const button = document.createElement("button"); 
      button.onclick = () => { 
         if (mode.redirectCanvas) 
            mode.redirectCanvas = null; 
         else 
            mode.redirectCanvas = redirectCanvas; 
         updateButtonText(); 
      } 
      output.appendChild(button); 
 
      const updateButtonText = () => { 
         button.innerHTML = !mode.redirectCanvas ? "Redirect Render" : "Render on Viewer"; 
      } 
      updateButtonText(); 
 
      // Add the mode to the viewer 
      viewer.interactiveModes.clear(); 
      viewer.interactiveModes.add(mode); 
 
      // Add a select element for the shapes 
      const shapeSelect = document.createElement("select"); 
      output.appendChild(shapeSelect); 
 
      let keys: string[] = Object.keys(lt.Controls.ImageViewerSpyGlassShape); 
      keys.forEach((key) => { 
         if (!isNaN(Number(lt.Controls.ImageViewerSpyGlassShape[key])) && key !== "__enum") { 
            const option = document.createElement("option"); 
            option.innerHTML = key; 
            shapeSelect.appendChild(option); 
         } 
      }); 
 
      shapeSelect.selectedIndex = lt.Controls.ImageViewerSpyGlassShape.ellipse; 
      mode.shape = lt.Controls.ImageViewerSpyGlassShape.ellipse; 
      shapeSelect.addEventListener("change", () => { 
         mode.shape = shapeSelect.selectedIndex; 
      }); 
 
      // Add the canvas 
      const container = document.createElement("div"); 
      container.appendChild(redirectCanvas); 
      output.appendChild(container); 
   } 
} 
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 SpyGlassInteractiveMode_RedirectCanvasExample { 
   viewerExample; 
   constructor() { 
      this.viewerExample = new ImageViewer_Example(this.run); 
   } 
 
   run = (viewer) => { 
      const output = document.getElementById("output"); 
 
      // The width and height of our redirect canvas 
      const canvasWidth = 250; 
      const canvasHeight = 250; 
 
      // Create the redirect canvas 
      const redirectCanvas = document.createElement("canvas"); 
      redirectCanvas.style.border = "1px solid black"; 
      redirectCanvas.width = canvasWidth; 
      redirectCanvas.height = canvasHeight; 
 
      // Create the SpyGlass mode 
      const mode = new lt.Controls.ImageViewerSpyGlassInteractiveMode(); 
      mode.workCompleted.add((sender, e) => { 
         if (mode.redirectCanvas) { 
            // Clear after drawing on redirected canvas 
            const ctx = mode.redirectCanvas.getContext("2d"); 
            ctx.clearRect(0, 0, mode.redirectCanvas.width, mode.redirectCanvas.height) 
         } 
      }); 
      mode.size = lt.LeadSizeD.create(canvasWidth, canvasHeight); 
      mode.redirectCanvas = redirectCanvas; 
      mode.backgroundColor = "yellow"; 
      mode.crosshairColor = "red"; 
 
      mode.drawImage.add((sender, e) => { 
         const rect = e.destinationRectangle; 
         const ctx = e.context; 
 
         ctx.save(); 
 
         // Undo offset of the spyglass 
         ctx.translate(-rect.x, -rect.y); 
 
         // We could do anything here. For example, ImageViewerMagnifyGlassInteractiveMode zooms in. 
         // We will draw additional text over the image. 
 
         // Clip to the ImageViewer (optional) 
         const bounds = viewer.getViewBounds(false, true); 
         ctx.beginPath(); 
         ctx.rect(bounds.x, bounds.y, bounds.width, bounds.height); 
         ctx.closePath(); 
         ctx.clip(); 
 
         // Draw the view 
         viewer.renderRedirect(ctx, new lt.Controls.ImageViewerRenderRedirectOptions(), lt.LeadRectD.empty); 
 
         // Draw some text on top 
         ctx.fillStyle = "white"; 
         ctx.strokeStyle = "white"; 
         ctx.font = "75px Times New Roman"; 
         ctx.fillText("Spyglass", bounds.x + (bounds.width / 2) - 100, bounds.y + (bounds.height / 2)); 
 
         ctx.restore(); 
      }); 
 
      // Add a toggle button 
      const button = document.createElement("button"); 
      button.onclick = () => { 
         if (mode.redirectCanvas) 
            mode.redirectCanvas = null; 
         else 
            mode.redirectCanvas = redirectCanvas; 
         updateButtonText(); 
      } 
      output.appendChild(button); 
 
      const updateButtonText = () => { 
         button.innerHTML = !mode.redirectCanvas ? "Redirect Render" : "Render on Viewer"; 
      } 
      updateButtonText(); 
 
      // Add the mode to the viewer 
      viewer.interactiveModes.clear(); 
      viewer.interactiveModes.add(mode); 
 
      // Add a select element for the shapes 
      const shapeSelect = document.createElement("select"); 
      output.appendChild(shapeSelect); 
 
      let keys = Object.keys(lt.Controls.ImageViewerSpyGlassShape); 
      keys.forEach((key) => { 
         if (!isNaN(Number(lt.Controls.ImageViewerSpyGlassShape[key])) && key !== "__enum") { 
            const option = document.createElement("option"); 
            option.innerHTML = key; 
            shapeSelect.appendChild(option); 
         } 
      }); 
 
      shapeSelect.selectedIndex = lt.Controls.ImageViewerSpyGlassShape.ellipse; 
      mode.shape = lt.Controls.ImageViewerSpyGlassShape.ellipse; 
      shapeSelect.addEventListener("change", () => { 
         mode.shape = shapeSelect.selectedIndex; 
      }); 
 
      // Add the canvas 
      const container = document.createElement("div"); 
      container.appendChild(redirectCanvas); 
      output.appendChild(container); 
   } 
} 
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 | RedirectCanvas</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.RedirectCanvas(); 
 
   }; 
</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.