webgl学习笔记四-动画

写在前面

建议先阅读下前面我的三篇文章。

webgl学习笔记一-绘图单点

webgl学习笔记二-绘图多点

webgl学习笔记三-平移旋转缩放

下面我们将讲解下如何让一个正方形动起来~不断擦除和重绘正方形,并且每次重绘时轻微地改变其角度。

demo

吊下胃口

html

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>Title</title>

</head>

<script src="../../lib/cuon-matrix.js"></script>

<body>

<canvas id="canvas" width="200px" height="200px"></canvas>

</body>

</html>

JavaScript

<script>

    // 顶点着色器程序

    var VSHADER_SOURCE =

        'attribute vec4 a_Position;\n' +

        'uniform mat4 u_ModelMatrix;\n' +

        'void main() {\n' +

        '  gl_Position = u_ModelMatrix * a_Position;\n' +

        '}\n';

    // 片元着色器程序

    var FSHADER_SOURCE =

        'void main() {\n' +

        '  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n' +

        '}\n';

    // Rotation angle (degrees/second)

    var ANGLE_STEP = 45.0;

    function main() {

        // init gl

        var gl = initCanvas();

        // Initialize shaders

        var shaderProgram = initShader(gl, VSHADER_SOURCE, FSHADER_SOURCE).program;

        // Write the positions of vertices to a vertex shader

        var n = initVertexBuffers(gl, shaderProgram);

        if (n < 0) {

            console.log('Failed to set the positions of the vertices');

            return;

        }

        // Specify the color for clearing <canvas>

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

        // Get storage location of u_ModelMatrix

        var u_ModelMatrix = gl.getUniformLocation(shaderProgram, 'u_ModelMatrix');

        if (!u_ModelMatrix) {

            console.log('Failed to get the storage location of u_ModelMatrix');

            return;

        }

        // Current rotation angle

        var currentAngle = 0.0;

        // Model matrix

        var modelMatrix = new Matrix4();

        // Start drawing

        var tick = function () {

            currentAngle = animate(currentAngle);  // Update the rotation angle

            draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix);   // Draw the triangle

            requestAnimationFrame(tick, canvas); // Request that the browser ?calls tick

        };

        tick();

    }

    // init cavas webgl context

    function initCanvas() {

        //获取canvas元素

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

        //获取绘制二维上下文

        var gl = canvas.getContext('webgl');

        if (!gl) {

            console.log("Failed");

            return null;

        }

        return gl;

    }

    // init shader

    function initShader(gl, vshader_source, fshader_source) {

        //编译着色器

        var vertShader = gl.createShader(gl.VERTEX_SHADER);

        gl.shaderSource(vertShader, vshader_source);

        gl.compileShader(vertShader);

        var fragShader = gl.createShader(gl.FRAGMENT_SHADER);

        gl.shaderSource(fragShader, fshader_source);

        gl.compileShader(fragShader);

        //合并程序

        var program = gl.createProgram();

        gl.attachShader(program, vertShader);

        gl.attachShader(program, fragShader);

        gl.linkProgram(program);

        gl.useProgram(program);

        return {

            program: program

        }

    }

    function initVertexBuffers(gl, shaderProgram) {

        var vertices = new Float32Array([

            -0.5, 0.5, -0.5, -0.5, 0.5, 0.5, 0.5, -0.5

        ]);

        var n = 4;   // The number of vertices

        // Create a buffer object

        var vertexBuffer = gl.createBuffer();

        if (!vertexBuffer) {

            console.log('Failed to create the buffer object');

            return -1;

        }

        // Bind the buffer object to target

        gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);

        // Write date into the buffer object

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

        // Assign the buffer object to a_Position variable

        var a_Position = gl.getAttribLocation(shaderProgram, 'a_Position');

        if (a_Position < 0) {

            console.log('Failed to get the storage location of a_Position');

            return -1;

        }

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

        // Enable the assignment to a_Position variable

        gl.enableVertexAttribArray(a_Position);

        return n;

    }

    function draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix) {

        // Set the rotation matrix

        modelMatrix.setRotate(currentAngle, 0, 0, 1);

        modelMatrix.translate(0.35, 0, 0);

        // Pass the rotation matrix to the vertex shader

        gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);

        // Clear <canvas>

        gl.clear(gl.COLOR_BUFFER_BIT);

        // Draw the rectangle

        gl.drawArrays(gl.TRIANGLE_STRIP, 0, n);

    }

    // Last time that this function was called

    var g_last = Date.now();

    function animate(angle) {

        // Calculate the elapsed time

        var now = Date.now();

        var elapsed = now - g_last;

        g_last = now;

        // Update the current rotation angle (adjusted by the elapsed time)

        var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0;

        return newAngle %= 360;

    }

    main();

</script>

巴特西

webgl学习笔记四-动画

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