feat(RenderWindowViewNode): add getComputedDevicePixelRatio

vtkRenderWindowViewNode.getComputedDevicePixelRatio uses DOM
container CSS pixel size and the user set renderer pixel size.

Author: PaulHax

Sources/Rendering/OpenGL/RenderWindow/index.d.ts

@@ -361,6 +361,18 @@ export interface vtkOpenGLRenderWindow extends vtkOpenGLRenderWindowBase {
 	 *
 	 */
 	getVrResolution(): Vector2;
+
+	/**
+	 * Use to scale the size of a rendered canvas pixel to a browser CSS pixel.  
+	 * `const cssPixelWidth = renderedPixelWidth / apiRenderWindow.getComputedDevicePixelRatio()`
+	 * Rather than using window.devicePixelRatio directly, the device pixel ratio is inferred
+	 * from the container CSS pixel size and rendered image pixel size. The user can reduce the rendered size.
+	 * `apiSpecificRenderWindow.setSize(Math.floor(container.width * window.devicePixelRatio / 2), Math.floor(container.height * window.devicePixelRatio / 2))`
+	 * 
+	 * @see getContainerSize()
+	 * @see getSize()
+	 */
+	getComputedDevicePixelRatio(): number;
 }
 
 /**

Sources/Rendering/SceneGraph/RenderWindowViewNode/index.js

@@ -135,14 +135,19 @@ function vtkRenderWindowViewNode(publicAPI, model) {
     return publicAPI.displayToNormalizedDisplay(x2, y2, z);
   };
 
+  publicAPI.getComputedDevicePixelRatio = () =>
+    model.size[0] / publicAPI.getContainerSize()[0];
+
+  publicAPI.getContainerSize = () => {
+    macro.vtkErrorMacro('not implemented');
+  };
+
   publicAPI.getPixelData = (x1, y1, x2, y2) => {
     macro.vtkErrorMacro('not implemented');
-    return undefined;
   };
 
   publicAPI.createSelector = () => {
     macro.vtkErrorMacro('not implemented');
-    return undefined;
   };
 }