onnxruntime/js/web/lib/onnxjs/backends/webgl/webgl-context-factory.ts

// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

import {Logger} from '../../instrument';

import {WebGLContext} from './webgl-context';

const cache: {[contextId: string]: WebGLContext} = {};

/**
 * This factory function creates proper WebGLRenderingContext based on
 * the current browsers capabilities
 * The order is from higher/most recent versions to most basic
 */
export function createWebGLContext(contextId?: 'webgl'|'webgl2'): WebGLContext {
  let context: WebGLContext|undefined;
  if ((!contextId || contextId === 'webgl2') && 'webgl2' in cache) {
    context = cache.webgl2;
  } else if ((!contextId || contextId === 'webgl') && 'webgl' in cache) {
    context = cache.webgl;
  }

  context = context || createNewWebGLContext(contextId);
  contextId = contextId || context.version === 1 ? 'webgl' : 'webgl2';
  const gl = context.gl;

  cache[contextId] = context;

  if (gl.isContextLost()) {
    delete cache[contextId];
    return createWebGLContext(contextId);
  }

  gl.disable(gl.DEPTH_TEST);
  gl.disable(gl.STENCIL_TEST);
  gl.disable(gl.BLEND);
  gl.disable(gl.DITHER);
  gl.disable(gl.POLYGON_OFFSET_FILL);
  gl.disable(gl.SAMPLE_COVERAGE);
  gl.enable(gl.SCISSOR_TEST);
  gl.enable(gl.CULL_FACE);
  gl.cullFace(gl.BACK);

  return context;
}

export function createNewWebGLContext(contextId?: 'webgl'|'webgl2'): WebGLContext {
  const canvas = createCanvas();
  const contextAttributes: WebGLContextAttributes = {
    alpha: false,
    depth: false,
    antialias: false,
    stencil: false,
    preserveDrawingBuffer: false,
    premultipliedAlpha: false,
    failIfMajorPerformanceCaveat: false
  };
  let gl: WebGLRenderingContext|null;
  const ca = contextAttributes;
  if (!contextId || contextId === 'webgl2') {
    gl = canvas.getContext('webgl2', ca);
    if (gl) {
      try {
        return new WebGLContext(gl, 2);
      } catch (err) {
        Logger.warning('GlContextFactory', `failed to create WebGLContext using contextId 'webgl2'. Error: ${err}`);
      }
    }
  }
  if (!contextId || contextId === 'webgl') {
    gl = canvas.getContext('webgl', ca) || canvas.getContext('experimental-webgl', ca) as WebGLRenderingContext;
    if (gl) {
      try {
        return new WebGLContext(gl, 1);
      } catch (err) {
        Logger.warning(
            'GlContextFactory',
            `failed to create WebGLContext using contextId 'webgl' or 'experimental-webgl'. Error: ${err}`);
      }
    }
  }

  throw new Error('WebGL is not supported');
}

function createCanvas(): HTMLCanvasElement {
  const canvas: HTMLCanvasElement = document.createElement('canvas');
  canvas.width = 1;
  canvas.height = 1;
  return canvas;
}