Source: packages/canvas/canvas-graphics/src/Graphics.js

import { Graphics } from '@pixi/graphics';
import { CanvasRenderer } from '@pixi/canvas-renderer';
import { RenderTexture, Texture } from '@pixi/core';
import { Matrix } from '@pixi/math';

let canvasRenderer;
const tempMatrix = new Matrix();

/**
 * Generates a canvas texture.
 * @method generateCanvasTexture
 * @memberof PIXI.Graphics#
 * @param {number} scaleMode - The scale mode of the texture.
 * @param {number} resolution - The resolution of the texture.
 * @return {PIXI.Texture} The new texture.
 */
Graphics.prototype.generateCanvasTexture = function generateCanvasTexture(scaleMode, resolution = 1)
{
    const bounds = this.getLocalBounds();

    const canvasBuffer = RenderTexture.create(bounds.width, bounds.height, scaleMode, resolution);

    if (!canvasRenderer)
    {
        canvasRenderer = new CanvasRenderer();
    }

    this.transform.updateLocalTransform();
    this.transform.localTransform.copyTo(tempMatrix);

    tempMatrix.invert();

    tempMatrix.tx -= bounds.x;
    tempMatrix.ty -= bounds.y;

    canvasRenderer.render(this, canvasBuffer, true, tempMatrix);

    const texture = Texture.fromCanvas(canvasBuffer.baseTexture._canvasRenderTarget.canvas, scaleMode, 'graphics');

    texture.baseTexture.resolution = resolution;
    texture.baseTexture.update();

    return texture;
};

/**
 * Renders the object using the Canvas renderer
 *
 * @method _renderCanvas
 * @memberof PIXI.Graphics#
 * @private
 * @param {PIXI.CanvasRenderer} renderer - The renderer
 */
Graphics.prototype._renderCanvas = function _renderCanvas(renderer)
{
    if (this.isMask === true)
    {
        return;
    }

    renderer.plugins.graphics.render(this);
};