<!DOCTYPE html>
<html>
<head>
<title>WebGL Enable Vertex Attrib Zero Test</title>
<script src="../../../resources/js-test.js"></script>
<script src="resources/webgl-test.js"> </script>
<script src="resources/webgl-test-utils.js"> </script>
</head>
<body>
<canvas id="example" width="50" height="50">
</canvas>
<div id="description"></div>
<div id="console"></div>
<script id="vshader" type="x-shader/x-vertex">
    attribute vec4 vPosition;
    void main()
    {
        gl_Position = vPosition;
    }
</script>

<script id="fshader" type="x-shader/x-fragment">
    void main()
    {
        gl_FragColor = vec4(0.0,0.0,0.0,0.0);
    }
</script>

<script>
description("Test some of the issues of the difference between attrib 0 on OpenGL vs WebGL");
debug("");
var wtu = WebGLTestUtils;
var canvas = document.getElementById("example");
var gl = wtu.create3DContext(canvas);

function setup(numVerts, attribIndex) {
  var program = wtu.setupProgram(
      gl,
      [wtu.loadShaderFromScript(gl, 'vshader', gl.VERTEX_SHADER),
       wtu.loadShaderFromScript(gl, 'fshader', gl.FRAGMENT_SHADER)],
      ['vPosition'], [attribIndex]);
  // draw with something on attrib zero with a small number of vertices
  var vertexObject = gl.createBuffer();
  g_program = program;
  g_attribLocation = attribIndex;
  shouldBe("g_attribLocation", "gl.getAttribLocation(g_program, 'vPosition')");
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexObject);
  gl.bufferData(
      gl.ARRAY_BUFFER, new Float32Array(numVerts * 3), gl.STATIC_DRAW);
  gl.vertexAttribPointer(attribIndex, 3, gl.FLOAT, false, 0, 0);
  var indices = new Uint16Array(numVerts);
  for (var ii = 0; ii < numVerts; ++ii) {
    indices[ii] = ii;
  }
  var indexBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
  gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);
  return program;
}

var p1 = setup(3, 0);
var p2 = setup(60000, 3);

for (var ii = 0; ii < 5; ++ii) {
  gl.useProgram(p1);
  gl.enableVertexAttribArray(0);
  gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0);
  glErrorShouldBe(
      gl, gl.NO_ERROR,
      "drawing using attrib 0 with 3 verts");

  gl.useProgram(p2);
  gl.enableVertexAttribArray(3);
  gl.drawArrays(gl.LINES, 0, 60000);
  glErrorShouldBe(
      gl, gl.NO_ERROR,
      "drawing using attrib 3 with 60000 verts");
}

wtu.checkCanvas(gl, [0, 0, 0, 0], "canvas should be 0, 0, 0, 0");
</script>
</body>
</html>