<!--
Copyright (c) 2019 The Khronos Group Inc.
Use of this source code is governed by an MIT-style license that can be
found in the LICENSE.txt file.
-->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<!-- This is a visual test that programs must have both a vertex and
     fragment shader attached; the fixed function pipeline on the
     desktop must remain disabled. -->
<script type="application/javascript">
function log() {
  var s = "";
  for (var i = 0; i < arguments.length; ++i) {
    s += arguments[i] + " ";
  }
  document.getElementById("log").innerHTML += s + "<br>";
}

function go() {
  var gl = document.getElementById("c").getContext("experimental-webgl");

  gl.clearColor(0.0, 0.0, 0.0, 0.0);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var vs = gl.createShader(gl.VERTEX_SHADER);
  gl.shaderSource(vs, "attribute vec4 aVertex; attribute vec4 aColor; varying vec4 vColor; void main() { vColor = aColor; gl_Position = aVertex; }");
  gl.compileShader(vs);

  var fs = gl.createShader(gl.FRAGMENT_SHADER);
  gl.shaderSource(fs, "precision mediump float; varying vec4 vColor; void main() { gl_FragColor = vColor; }");
  gl.compileShader(fs);

  var prog = gl.createProgram();
  gl.attachShader(prog, vs);
  // don't attach a fragment shader -- may use fixed pipeline on desktop if the implementation doesn't check!
  //gl.attachShader(prog, fs);

  gl.bindAttribLocation(prog, 0, "aVertex");
  gl.bindAttribLocation(prog, 1, "aColor");

  gl.linkProgram(prog);

  var vbuf = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, vbuf);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
      -1.0, -1.0, 0.0, 1.0,
      -1.0, 1.0, 0.0, 1.0,
      1.0, -1.0, 0.0, 1.0,
      1.0, 1.0, 0.0, 1.0]), gl.STATIC_DRAW);
  gl.vertexAttribPointer(0, 4, gl.FLOAT, false, 0, 0);

  var cbuf = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, cbuf);
  gl.bufferData(gl.ARRAY_BUFFER, new Uint8Array([255, 0, 0,
                                                 0, 255, 0,
                                                 0, 0, 255,
                                                 255, 255, 0]), gl.STATIC_DRAW);
  gl.vertexAttribPointer(1, 3, gl.UNSIGNED_BYTE, false, 0, 0);

  gl.enableVertexAttribArray(0);
  gl.enableVertexAttribArray(1);

  gl.useProgram(prog);

  gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);

  log("glError", "0x" + gl.getError().toString(16));
}
</script>
</head>

<body onload="go()">
<p>Should be green in the rectangle below:</p>
<canvas style="background: green;" id="c"></canvas>
<div id="log"></div>
</body>
</html>
