runCopyShader( gl, width, height, loc_a_pos, programs, colorTexture, vbo ) {
    gl.bindFramebuffer(gl.FRAMEBUFFER, null )

    gl.bindTexture(gl.TEXTURE_2D, colorTexture)
    gl.viewport(0, 0, width, height )

    gl.bindBuffer( gl.ARRAY_BUFFER, vbo )
    gl.useProgram( programs[1] )

    const u_resolution = gl.getUniformLocation(programs[1], "resolution" )
    gl.uniform2f( u_resolution, width, height )

    gl.drawArrays( gl.TRIANGLES, 0, 6 )
  }
****** UNCOMMENT THIS LINE TO CHECK MARCHING.JS DEPTH OUPTUT **************