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<!-- Ported from the OpenGL Samples Pack https://github.com/g-truc/ogl-samples/blob/master/tests/gl-320-texture-fetch.cpp -->

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<title>WebGL 2 Samples - texture_fetch</title>

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<div id="info">WebGL 2 Samples - texture_fetch</div>

<p id="description">

GLSL built-in function texelFetch is used for manual bilinear filtering.

</p>

<!-- WebGL 2 shaders -->

<script id="vs" type="x-shader/x-vertex">

#version 300 es

#define POSITION_LOCATION 0

#define TEXCOORD_LOCATION 4

precision highp float;

precision highp int;

uniform mat4 MVP;

layout(location = POSITION_LOCATION) in vec2 position;

layout(location = TEXCOORD_LOCATION) in vec2 texcoord;

out vec2 v_st;

void main()

{

v_st = texcoord;

gl_Position = MVP * vec4(position, 0.0, 1.0);

}

</script>

<script id="fs" type="x-shader/x-fragment">

#version 300 es

precision highp float;

precision highp int;

uniform sampler2D diffuse;

in vec2 v_st;

out vec4 color;

void main()

{

vec2 size = vec2(textureSize(diffuse, 0) - 1);

vec2 texcoord = v_st * size;

ivec2 coord = ivec2(texcoord);

vec4 texel00 = texelFetch(diffuse, coord + ivec2(0, 0), 0);

vec4 texel10 = texelFetch(diffuse, coord + ivec2(1, 0), 0);

vec4 texel11 = texelFetch(diffuse, coord + ivec2(1, 1), 0);

vec4 texel01 = texelFetch(diffuse, coord + ivec2(0, 1), 0);

vec2 sampleCoord = fract(texcoord.xy);

vec4 texel0 = mix(texel00, texel01, sampleCoord.y);

vec4 texel1 = mix(texel10, texel11, sampleCoord.y);

color = mix(texel0, texel1, sampleCoord.x);

}

</script>

<script src="utility.js"></script>

<script>

(function () {

'use strict';

var canvas = document.createElement('canvas');

canvas.width = Math.min(window.innerWidth, window.innerHeight);

canvas.height = canvas.width;

document.body.appendChild(canvas);

var gl = canvas.getContext( 'webgl2', { antialias: false } );

var isWebGL2 = !!gl;

if(!isWebGL2) {

document.getElementById('info').innerHTML = 'WebGL 2 is not available. See <a href="https://www.khronos.org/webgl/wiki/Getting_a_WebGL_Implementation">How to get a WebGL 2 implementation</a>';

return;

}

// -- Init program

var program = createProgram(gl, getShaderSource('vs'), getShaderSource('fs'));

var mvpLocation = gl.getUniformLocation(program, 'MVP');

var diffuseLocation = gl.getUniformLocation(program, 'diffuse');

// -- Init buffers: vec2 Position, vec2 Texcoord

var positions = new Float32Array([

-1.0, -1.0,

1.0, -1.0,

1.0, 1.0,

1.0, 1.0,

-1.0, 1.0,

-1.0, -1.0

]);

var vertexPosBuffer = gl.createBuffer();

gl.bindBuffer(gl.ARRAY_BUFFER, vertexPosBuffer);

gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);

gl.bindBuffer(gl.ARRAY_BUFFER, null);

var texCoords = new Float32Array([

0.0, 1.0,

1.0, 1.0,

1.0, 0.0,

1.0, 0.0,

0.0, 0.0,

0.0, 1.0

]);

var vertexTexBuffer = gl.createBuffer();

gl.bindBuffer(gl.ARRAY_BUFFER, vertexTexBuffer);

gl.bufferData(gl.ARRAY_BUFFER, texCoords, gl.STATIC_DRAW);

gl.bindBuffer(gl.ARRAY_BUFFER, null);

// -- Init VertexArray

var vertexArray = gl.createVertexArray();

gl.bindVertexArray(vertexArray);

var vertexPosLocation = 0; // set with GLSL layout qualifier

gl.enableVertexAttribArray(vertexPosLocation);

gl.bindBuffer(gl.ARRAY_BUFFER, vertexPosBuffer);

gl.vertexAttribPointer(vertexPosLocation, 2, gl.FLOAT, false, 0, 0);

gl.bindBuffer(gl.ARRAY_BUFFER, null);

var vertexTexLocation = 4; // set with GLSL layout qualifier

gl.enableVertexAttribArray(vertexTexLocation);

gl.bindBuffer(gl.ARRAY_BUFFER, vertexTexBuffer);

gl.vertexAttribPointer(vertexTexLocation, 2, gl.FLOAT, false, 0, 0);

gl.bindBuffer(gl.ARRAY_BUFFER, null);

gl.bindVertexArray(null);

loadImage('../assets/img/Di-3d.png', function(image) {

// -- Init Texture

var texture = gl.createTexture();

gl.activeTexture(gl.TEXTURE0);

gl.bindTexture(gl.TEXTURE_2D, texture);

gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, false);

gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);

// -- Render

gl.clearColor(0.0, 0.0, 0.0, 1.0);

gl.clear(gl.COLOR_BUFFER_BIT);

var matrix = new Float32Array([

0.5, 0.0, 0.0, 0.0,

0.0, 0.5, 0.0, 0.0,

0.0, 0.0, 0.5, 0.0,

0.0, 0.0, 0.0, 1.0

]);

gl.useProgram(program);

gl.uniformMatrix4fv(mvpLocation, false, matrix);

gl.uniform1i(diffuseLocation, 0);

gl.bindVertexArray(vertexArray);

gl.drawArrays(gl.TRIANGLES, 0, 6);

// Delete WebGL resources

gl.deleteBuffer(vertexPosBuffer);

gl.deleteBuffer(vertexTexBuffer);

gl.deleteTexture(texture);

gl.deleteProgram(program);

gl.deleteVertexArray(vertexArray);

});

})();

</script>

<div id="highlightedLines" style="display: none">#L58-L61</div>

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