<!--
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">
<link rel="stylesheet" href="../../resources/js-test-style.css"/>
<script src="../../js/js-test-pre.js"></script>
<script src="../../js/webgl-test-utils.js"></script>
</head>
<body>
<div id="description"></div>
<div id="console"></div>
<canvas id="canvas" width="4" height="4"></canvas>
<script id="vshader" type="x-shader/x-vertex">
attribute vec3 a_pos;
attribute vec4 a_color;
varying vec4 v_color;

void main()
{
    v_color = a_color;
    gl_Position = vec4(a_pos.xyz, 1.0);
}
</script>

<script id="fshader" type="x-shader/x-fragment">
precision mediump float;

varying vec4 v_color;

void main()
{
    gl_FragColor = v_color;
}
</script>

<script>
"use strict";

description("when antialias is enabled, verify default fbo pixels would not be changed between two readPixels without drawing operations");
var wtu = WebGLTestUtils;
var N = 4;

var vertices = new Float32Array([
         1.0, 1.0, 0.0,
        -1.0, -1.0, 0.0]);
var colors = new Uint8Array([
        255, 0, 0, 255,
        255, 0, 0, 255]);

var canvas = document.getElementById('canvas');
var gl = wtu.create3DContext(canvas, {antialias: true});

if (!gl) {
  testFailed("context does not exist");
} else {
  testPassed("context exists");

  var program = wtu.setupProgram(gl, ["vshader", "fshader"], ["a_pos", "a_color"]);
  gl.clearColor(0, 0, 0, 1);
  gl.clear(gl.COLOR_BUFFER_BIT);

  var colorOffset = vertices.byteLength;
  var vbo = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, vbo);
  gl.bufferData(gl.ARRAY_BUFFER, colorOffset + colors.byteLength, gl.STATIC_DRAW);
  gl.bufferSubData(gl.ARRAY_BUFFER, 0, vertices);
  gl.bufferSubData(gl.ARRAY_BUFFER, colorOffset, colors);

  gl.vertexAttribPointer(0, 3, gl.FLOAT, false, 0, 0);
  gl.enableVertexAttribArray(0);
  gl.vertexAttribPointer(1, 4, gl.UNSIGNED_BYTE, true, 0, colorOffset);
  gl.enableVertexAttribArray(1);
  gl.drawArrays(gl.LINES, 0, vertices.length / 3);

  var result_1 = new Uint8Array(N * N * 4);
  var result_2 = new Uint8Array(N * N * 4);
  gl.readPixels(0, 0, N, N, gl.RGBA, gl.UNSIGNED_BYTE, result_1);
  gl.readPixels(0, 0, N, N, gl.RGBA, gl.UNSIGNED_BYTE, result_2);
  wtu.glErrorShouldBe(gl, gl.NO_ERROR);

  var tolerance = 0;
  var diff = new Uint8Array(N * N * 4);
  var failed = wtu.comparePixels(result_1, result_2, tolerance, diff);

  if (failed) {
    testFailed("default fbo pixels had be changed between two readPixels without drawing operations");
  } else {
    testPassed("default fbo pixels had not be changed between two readPixels without drawing operations.");
  }

  gl.bindBuffer(gl.ARRAY_BUFFER, null);
  gl.deleteBuffer(vbo);
}

var successfullyParsed = true;
</script>
<script src="../../js/js-test-post.js"></script>
</body>
</html>
