Babylon.js/src/Engines/Extensions/engine.readTexture.ts

import { ThinEngine } from "../../Engines/thinEngine";
import { InternalTexture } from '../../Materials/Textures/internalTexture';
import { Nullable } from '../../types';

declare module "../../Engines/thinEngine" {
    export interface ThinEngine {
        /** @hidden */
        _readTexturePixels(texture: InternalTexture, width: number, height: number, faceIndex?: number, level?: number, buffer?: Nullable<ArrayBufferView>): ArrayBufferView;
    }
}

ThinEngine.prototype._readTexturePixels = function(texture: InternalTexture, width: number, height: number, faceIndex = -1, level = 0, buffer: Nullable<ArrayBufferView> = null): ArrayBufferView {
    let gl = this._gl;
    if (!this._dummyFramebuffer) {
        let dummy = gl.createFramebuffer();

        if (!dummy) {
            throw new Error("Unable to create dummy framebuffer");
        }

        this._dummyFramebuffer = dummy;
    }
    gl.bindFramebuffer(gl.FRAMEBUFFER, this._dummyFramebuffer);

    if (faceIndex > -1) {
        gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_CUBE_MAP_POSITIVE_X + faceIndex, texture._webGLTexture, level);
    } else {
        gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture._webGLTexture, level);
    }

    let readType = (texture.type !== undefined) ? this._getWebGLTextureType(texture.type) : gl.UNSIGNED_BYTE;

    switch (readType) {
        case gl.UNSIGNED_BYTE:
            if (!buffer) {
                buffer = new Uint8Array(4 * width * height);
            }
            readType = gl.UNSIGNED_BYTE;
            break;
        default:
            if (!buffer) {
                buffer = new Float32Array(4 * width * height);
            }
            readType = gl.FLOAT;
            break;
    }

    gl.readPixels(0, 0, width, height, gl.RGBA, readType, <DataView>buffer);
    gl.bindFramebuffer(gl.FRAMEBUFFER, this._currentFramebuffer);

    return buffer;
};