Webgl triangle drawing

var canvas = document.getElementById(‘myCanvas’) var gl = canvas.getContext(‘webgl’) var program = gl.createProgram() var VSHADER_SOURCE, FSHADER_SOURCE

VSHADER_SOURCE = ‘attribute vec4 a_Position; \n’ + ‘uniform mat4 u_ModelMatrix; \n’ + ‘uniform mat4 u_ViewMatrix; \n’ + ‘void main () {\n’ + ‘gl_Position = u_ProjectionMartix u_ViewMatrix u_ModelMatrix * a_Position; FSHADER_SOURCE} \ n \ n ‘+’ ‘=’ void main () {\ n ‘+’ gl_FragColor = vec4 (1.0, 0.0, 0.0, 1.0); \n’ + ‘}\n’ var vertexShader, fragmentShader function createShader (gl, sourceCode, type) { // create shader var shader = gl.createShader(type) gl.shaderSource(shader,sourceCode) gl.compileShader(shader) return shader } // define vertex shader vertexShader = createShader(gl, VSHADER_SOURCE,gl.VERTEX_SHADER) //define frament shader fragmentShader = createShader(gl, FSHADER_SOURCE, gl.FRAGMENT_SHADER)

//attach shader to program gl.attachShader(program, vertexShader) gl.attachShader(program, fragmentShader)

//link program to context gl.linkProgram(program) gl.useProgram(program) gl.program = program

var currentAngle = 0 var g_last = Date.now()

var tick = function () { // update the new rotation angle animate() //draw draw() requestAnimationFrame(tick) } function initVertexBuffers (gl) { var vertices = new Float32Array([

0, 0.5, -0.5, -0.5, 0.5, -0.5]) var n = 3 var n = 3 vertexBuffer) // write data into the buffer object gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW) // get attribute a_Position address in vertex shader var a_Position = gl.getAttribLocation(gl.program, ‘a_Position’) gl.vertexattribPointer (a_Position, 2, gl.float, false, 0, 0)

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enable a_Position variable gl.enableVertexAttribArray(a_Position) return n } // write the positions of vertices to a vertex shader var n = initVertexBuffers(gl)

gl.clearColor(0, 0, 0, 1)

var u_ModelMatrix = gl.getUniformLocation(gl.program, ‘u_ModelMatrix’) var modelMatrix = new Matrix4()

Then pull up the game database: var u_ViewMatrix = gl.getUniformLocation(gl.program, ‘u_ViewMatrix’) var viewMatrix = new Matrix4() viewMatrix.lookAt(100, 100, 100, 0, 0, 0, 0, 1, 0)

var u_ProjectionMatrix = gl.getUniformLocation(gl.program, ‘u_ProjectionMatrix) var projectionMatrix = new Matrix4 () / / projectionMatrix perspective (120, 1, 0.1, Ortho (-1, 1, -1, 1, 0.1, 1000) ortho(-1, 1, -1, 0.1, 1000)

function animate () { var now = Date.now() var duration = now – g_last g_last = now currentAngle = currentAngle + duration / 1000 * 180 }

function draw () { // clear canvas and add background color modelMatrix.setRotate(currentAngle, 0, 1, 0) gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements) gl.uniformMatrix4fv(u_ViewMatrix, false, viewMatrix.elements) gl.uniformMatrix4fv(u_ProjectionMatrix, false, projectionMatrix.elements) gl.clear(gl.COLOR_BUFFER_BIT) gl.drawArrays(gl.TRIANGLES, 0, n) }

tick()