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Fragment Shader:
precision mediump float;
uniform vec2 uViewportSize;
varying vec2 vUV;
void main(void) {
gl_FragColor = vec4(vUV.x, vUV.y, 1.0, 1.0);
/*
//gl_FragCoord is a way of getting the pixel location
gl_FragColor = vec4(
gl_FragCoord.x/uViewportSize.x,
gl_FragCoord.y/uViewportSize.y,
1.0,
1.0
);
*/
}
Vertex Shader:
//Data from bufferData
attribute vec3 aVertexPosition;
attribute vec2 aVertexUV;
uniform mat4 uMVMatrix;
uniform mat4 uPMatrix;
uniform vec2 uViewportSize;
//These will be passed to the fragment shader and will be interpreted per
//pixel
varying vec2 vUV;
void main(void) {
gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
//The line below will ignore any translation of perspective matrix
//gl_Position = vec4(aVertexPosition, 1.0);
vUV = aVertexUV;
}
Program Source:
var gl;
function initGL(canvas) {
try {
//gl = canvas.getContext("webgl");
gl = canvas.getContext("experimental-webgl");
gl.viewportWidth = canvas.width;
gl.viewportHeight = canvas.height;
} catch (e) {
}
if (!gl) {
alert("Could not initialise WebGL, sorry :-(");
}
}
function getShader(gl, id) {
var shaderScript = document.getElementById(id);
if (!shaderScript) {
return null;
}
var str = "";
var k = shaderScript.firstChild;
while (k) {
if (k.nodeType == 3) {
str += k.textContent;
}
k = k.nextSibling;
}
var shader;
if (shaderScript.type == "x-shader/x-fragment") {
shader = gl.createShader(gl.FRAGMENT_SHADER);
} else if (shaderScript.type == "x-shader/x-vertex") {
shader = gl.createShader(gl.VERTEX_SHADER);
} else {
return null;
}
gl.shaderSource(shader, str);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert(gl.getShaderInfoLog(shader));
return null;
}
return shader;
}
var shaderProgram;
function initShaders() {
var fragmentShader = getShader(gl, "shader-fs");
var vertexShader = getShader(gl, "shader-vs");
shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
alert("Could not initialise shaders");
}
gl.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
shaderProgram.vertexUVAttribute = gl.getAttribLocation(shaderProgram, "aVertexUV");
gl.enableVertexAttribArray(shaderProgram.vertexUVAttribute);
shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
shaderProgram.ViewportSizeUniform = gl.getUniformLocation(shaderProgram, "uViewportSize");
}
var mvMatrix;
var pMatrix;
function setUniforms() {
gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
gl.uniform2f(
shaderProgram.ViewportSizeUniform,
gl.viewportWidth,
gl.viewportHeight
);
}
var squareVertexPositionBuffer;
var squareVertexUVBuffer;
function initBuffers() {
//Create Square Position Buffer
squareVertexPositionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
var vertices = [
1.0, 1.0, 0.0,
-1.0, 1.0, 0.0,
1.0, -1.0, 0.0,
-1.0, -1.0, 0.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
squareVertexPositionBuffer.itemSize = 3;
squareVertexPositionBuffer.numItems = 4;
//Create Square UV Buffer
squareVertexUVBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexUVBuffer);
var uvs = [
1.0, 1.0,
0.0, 1.0,
1.0, 0.0,
0.0, 0.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(uvs), gl.STATIC_DRAW);
squareVertexUVBuffer.itemSize = 2;
squareVertexUVBuffer.numItems = 4;
}
function drawScene() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
pMatrix = identity();
mvMatrix = identity();
//pMatrix = ortho(-1, 1, -1, 1, 0.01, 10);
//pMatrix = makePerspective(45 * Math.PI/180.0, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);
//mvMatrix = makeTranslation(0.0, 0.0, -0.01);
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, squareVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexUVBuffer);
gl.vertexAttribPointer(shaderProgram.vertexUVAttribute, squareVertexUVBuffer.itemSize, gl.FLOAT, false, 0, 0);
setUniforms();
gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems);
}
function webGLStart() {
var canvas = document.getElementById("webgl-canvas");
initGL(canvas);
initShaders();
initBuffers();
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.enable(gl.DEPTH_TEST);
drawScene();
}
webGLStart();