Hello,
I'm migrating a web mapping application from ESRI Javascript API v3 to ArcGIS Maps SDK v4. In the v3 code, I used getContext('2d') to get access to the canvas and getImageData() to get the pixel data (color RGB on a particular spot on the map).
With Maps SDK, it seems the map is drawn on a webgl2 canvas and getContext('2d') returns null. I tried getContext('webgl2', {preserveDrawingBuffer: true}) and readPixels() but it returns an empty array. So, I can't get the pixel data. It seems there is a way to preserve the drawing buffer of webgl2 canvas but I don't think it's possible because how to create a canvas is totally up to Maps SDK and I can't modify it.
So, my questions are:
- Is there a way to make readPixels() return useful information so I can get the color RGB of the pixel?
- Is there a way to force Maps SDK to use 2d canvas instead of webgl2 or setup the webgl canvas with drawing buffer on?
- Is there workaround to get the pixel color RGB?
Background: my application visualizes a mosaic dataset as an ImageryLayer and map services as MapImageLayers from our own ArcGIS Server and I want to allow users to get the color information in RGB when they mouse-over the map (layers). So, it's not "Identify". I use pixelFilter to render ImageryLayer. So, I know I can get the pixel data. But what I want to achieve is to get the pixel color upon a user action on both ImageryLayer and MapImageLayers.
And below is a simplified working code for the v3 application.
var x = evt.screenPoint.x;
var y = evt.screenPoint.y;
var canvasDiv = Ext.get(divId);
var canvasDom = canvasDiv.child("canvas", true);
var c2d = canvasDom.getContext('2d');
var pixelData = c2d.getImageData(x, y, 1, 1).data;
var rgb = {r: pixelData[0], g: pixelData[1], b: pixelData[2]};
// And show rgb in a popup.
