前面两节我们用平行光为正方体添加了光照，这节我们用一个点光源来为正方体添加光照。
point lighted cube.png
平行光只需要一个光线方向和光线颜色就可以描述。而点光源的光线方向是不确定的，取决于点光源的位置和照射到物体上的位置。所以这里的重点是针对每个顶点重新计算光线方向。
我们要把点光源位置和 model matrix 传进去来计算每个顶点的光线方向
uniform vec3 u_LightPosition;
uniform mat4 u_ModelMatrix;
之后就可以计算出每个顶点的光线方向了
// 针对每个顶点计算光线方向
vec4 vertexPosition = u_ModelMatrix * a_Position;
vec3 lightDirection = normalize(u_LightPosition - vec3(vertexPosition));
现在的正方体看起来其实还不是特别的真实，因为只针对每个顶点计算了光线方向，最终的颜色在各个顶点之间进行了插值，而实际上正方体上每一个点上的光线方向都是不同的。要更加逼真的光照效果下节我们来看针对每个 fragment 计算光照。
完整代码
<script id="vertex-shader" type="glsl">
attribute vec4 a_Position;
attribute vec4 a_Color;
attribute vec3 a_Normal;
uniform vec3 u_LightColor;
uniform vec3 u_LightPosition;
uniform vec3 u_AmbientLight;
uniform mat4 u_mvpMatrix;
uniform mat4 u_ModelMatrix;
uniform mat4 u_NormalMatrix;
varying vec4 v_Color;
void main() {
gl_Position = u_mvpMatrix * a_Position;
// 标准化（把长度变为 1 ）
vec3 normal = normalize(vec3(u_NormalMatrix * vec4(a_Normal,1.0)));
// 针对每个顶点计算光线方向
vec4 vertexPosition = u_ModelMatrix * a_Position;
vec3 lightDirection = normalize(u_LightPosition - vec3(vertexPosition));
float nDotL = max(dot(lightDirection, normal), 0.0);
vec3 diffuse = u_LightColor * a_Color.rgb * nDotL;
vec3 ambient = u_AmbientLight * a_Color.rgb;
v_Color = vec4(diffuse + ambient, a_Color.a);
}
</script>
<script id="fragment-shader" type="glsl">
precision mediump float;
varying vec4 v_Color;
void main() {
gl_FragColor = v_Color;
}
</script>
<script src="lib/cuon-matrix.js"></script>
<script src="lib/myutils.js"></script>
<script>
var VERTEX_SHADER_SOURCE = document.getElementById('vertex-shader').text;
var FRAGMENT_SHADER_SOURCE = document.getElementById('fragment-shader').text;
var canvas = document.getElementById("canvas");
var gl = canvas.getContext('webgl');
if (!initShaders(gl, VERTEX_SHADER_SOURCE, FRAGMENT_SHADER_SOURCE)) {
alert('Failed to init shaders');
}
var n = initVertexBuffers(gl);
var u_mvpMatrix = gl.getUniformLocation(gl.program, 'u_mvpMatrix');
var u_LightColor = gl.getUniformLocation(gl.program, 'u_LightColor');
var u_AmbientLight = gl.getUniformLocation(gl.program, 'u_AmbientLight');
var u_NormalMatrix = gl.getUniformLocation(gl.program, 'u_NormalMatrix');
var u_LightPosition = gl.getUniformLocation(gl.program, 'u_LightPosition');
var u_ModelMatrix = gl.getUniformLocation(gl.program, 'u_ModelMatrix');
// 设置光源颜色
gl.uniform3f(u_LightColor, 1.0, 1.0, 1.0);
// 设置点光源位置
gl.uniform3f(u_LightPosition, 2.3, 4.0, 3.5);
// 设置环境光颜色
gl.uniform3f(u_AmbientLight, 0.2, 0.2, 0.2);
// <projection matrix> * <view matrix>
var mvpMatrix = new Matrix4();
mvpMatrix.setPerspective(30, 1, 1, 100);
mvpMatrix.lookAt(6, 6, 14, 0, 0, 0, 0, 1, 0);
var modelMatrix = new Matrix4();
modelMatrix.rotate(90, 0, 1, 0);
gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);
mvpMatrix.multiply(modelMatrix);
gl.uniformMatrix4fv(u_mvpMatrix, false, mvpMatrix.elements);
// 计算法向量变换矩阵
var normalMatrix = new Matrix4();
normalMatrix.setInverseOf(modelMatrix);
normalMatrix.transpose();
gl.uniformMatrix4fv(u_NormalMatrix, false, normalMatrix.elements);
gl.enable(gl.DEPTH_TEST);
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);
function initVertexBuffers(gl) {
// Create a cube
// v6----- v5
// /| /|
// v1------v0|
// | | | |
// | |v7---|-|v4
// |/ |/
// v2------v3
var vertices = new Float32Array([
2.0, 2.0, 2.0, -2.0, 2.0, 2.0, -2.0, -2.0, 2.0, 2.0, -2.0, 2.0, // v0-v1-v2-v3 front
2.0, 2.0, 2.0, 2.0, -2.0, 2.0, 2.0, -2.0, -2.0, 2.0, 2.0, -2.0, // v0-v3-v4-v5 right
2.0, 2.0, 2.0, 2.0, 2.0, -2.0, -2.0, 2.0, -2.0, -2.0, 2.0, 2.0, // v0-v5-v6-v1 up
-2.0, 2.0, 2.0, -2.0, 2.0, -2.0, -2.0, -2.0, -2.0, -2.0, -2.0, 2.0, // v1-v6-v7-v2 left
-2.0, -2.0, -2.0, 2.0, -2.0, -2.0, 2.0, -2.0, 2.0, -2.0, -2.0, 2.0, // v7-v4-v3-v2 down
2.0, -2.0, -2.0, -2.0, -2.0, -2.0, -2.0, 2.0, -2.0, 2.0, 2.0, -2.0 // v4-v7-v6-v5 back
]);
var colors = new Float32Array([ // Colors
1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, // v0-v1-v2-v3 front
1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, // v0-v3-v4-v5 right
1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, // v0-v5-v6-v1 up
1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, // v1-v6-v7-v2 left
1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, // v7-v4-v3-v2 down
1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0 // v4-v7-v6-v5 back
]);
var normals = new Float32Array([ // Normal
0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, // v0-v1-v2-v3 front
1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, // v0-v3-v4-v5 right
0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, // v0-v5-v6-v1 up
-1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, // v1-v6-v7-v2 left
0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, // v7-v4-v3-v2 down
0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0 // v4-v7-v6-v5 back
]);
var indices = new Uint8Array([ // Indices of the vertices
0, 1, 2, 0, 2, 3, // front
4, 5, 6, 4, 6, 7, // right
8, 9, 10, 8, 10, 11, // up
12, 13, 14, 12, 14, 15, // left
16, 17, 18, 16, 18, 19, // down
20, 21, 22, 20, 22, 23 // back
]);
if (!initArrayBuffer(gl, vertices, 3, gl.FLOAT, 'a_Position')) {
return -1;
}
if (!initArrayBuffer(gl, colors, 3, gl.FLOAT, 'a_Color')) {
return -1;
}
if (!initArrayBuffer(gl, normals, 3, gl.FLOAT, 'a_Normal')) {
return -1;
}
var indexBuffer = gl.createBuffer();
if (!indexBuffer) {
console.log('Failed to create index buffer');
return -1;
}
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);
return indices.length;
}
function initArrayBuffer(gl, data, numOfComponents, dataType, attributeName) {
var buffer = gl.createBuffer();
if (!buffer) {
console.log('Failed to create buffer object');
return false;
}
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);
var attribute = gl.getAttribLocation(gl.program, attributeName);
gl.vertexAttribPointer(attribute, numOfComponents, dataType, false, 0, 0);
gl.enableVertexAttribArray(attribute);
return true;
}
</script>
