triangle

frag

uniform sampler2D tex;
varying vec2 vUv;

void main() {

  gl_FragColor = texture2D( tex, vUv );

}

geo

import * as three from 'three'

class Triangle extends three.BufferGeometry {

	constructor(){

		super()

		this.setIndex( [2, 1, 0] )

		this.addAttribute( 'position',  new three.Float32BufferAttribute( 
		    [
		       -1, -1, 0, 
		      -1,  4, 0, 
		       4, -1, 0
		    ]
		, 3 ));

		this.needsUpdate = true

	}

}

let tri = new Triangle()

export default tri;

vertex

varying vec2 vUv;

void main() {

  vUv = vec2(0.5)+(position.xy)*0.5;
  gl_Position = vec4( position.xy, 0.0,  1.0 );;

}