首页 > 代码库 > TeaPot 用webgl画茶壶(2) Phong Shading
TeaPot 用webgl画茶壶(2) Phong Shading
在Fragment Shader里应用Phong Shading使得茶壶更逼真。即使是单一颜色的茶壶,只要光源的位置变化,或眼睛的位置变化,看到的茶壶的各个部分的颜色明暗是不一定一样的。所谓Phong Shading就是Phong这个人提出的一种决定每个像素颜色的方法。
总的来说,我们希望看到怎样的茶壶?我们希望它跟真的一样,有光照着它,所以照到的地方亮,照不到的地方暗,迎着光的地方还有高亮反射光。
点e看到点p有颜色,是因为有光子从p跑到了e。点p有光子,除非p是光源,不然光子肯定是从别的地方跑来。这个别的地方之一,就是光源,有光源照着p。但是,如果没有光源的直射,比如拉上窗帘的房间里,还是可以看到p,因为p点周围无数个点(茶壶上其它部分,杯子,桌子等等)都往它发射着光子。这是别的地方之二,环境。
总结一下一个点p(不是光源),被在e点看到了,说明
1. 有光子从别的地方跑到了p。
两个可能的来处,一是光源,一是环境。
2.p点的光子又跑到了e
到达p的光子有三个可能,一是被吸收产生热量,二是打入内部又散射出来,三是直接从表面反射出去。被吸收的就不用考虑了,剩下的一部分散射,一部分反射,散射是指这一部分光子从p出来后往各个方向跑(当然还是沿着直线),有一个方向指向e,e会看到散射光。散射光往往代表p本来的颜色,反射光与p本来的颜色几乎无关,因为它没有进入p内部而是在p处改变了方向,它还是原来的光。因为环境给p的光子是从各个方向来的,不好分析它们的反射方向,数量又不大,所以一般认为从环境里到达p的光子全都散射出去了。
环境里到达p的光子强度是固定的,而且它到达茶壶其它p1,p2等等的光子强度一样。而同一个光源,给茶壶各个p,p1,p2的光子强度却不是固定的。这个强度的大小与入射角度有关。Lambertian表示可以用 cos(p的法向量n与入射光的反方向向量l的夹角)*L的强度 来代表光源L到达p的强度,也就是n=normalize(n),l=normalize(l),dot(n,l)*L的强度。dot(n,l)可能小于0,小于0代表光是从p背面照着它,所以没有光子跑到p,max(0, dot(n,l))*L的强度。
光源的反射部分的方向是可以算出的,是向量r。e-p与r的夹角越小,说明接收的反射的越多。也可以看,向量h与n的夹角,h=normalize(e-p+l)。
p点的颜色=环境光的强度与颜色*散射系数+光源强度与颜色*max(0, dot(n,l))*散射系数+光源强度与颜色*pow(dot(h,n),P)
散射系数与p本身颜色紧密相关。pow是为了快速缩小高亮大小,否则高亮不真。P是光滑系数。
pow(dot(h,n),P)是改良的Phong shading。Phong提出的是pow(max(0,dot(r,e-p)),P)。区别是当e-p与r是钝角时,改良后的Phong Shading依然会产生反射光。光滑的表面放大后依然粗糙,有面向各个方向的Microfacets。
http://opengl.datenwolf.net/gltut/html/Illumination/Tutorial%2011.html
<html> <head> <title>TeaPolt</title> </head> <body onl oad="main()"> <canvas id="viewPort" width="600" height="800"> This browser do not support webgl. </canvas> <script src="http://www.mamicode.com/examples/lib/cuon-matrix.js"></script> <script src="http://www.mamicode.com/TeaPotData.js"></script> <script> function main() { //alert("bb"); //get webgl context var viewPort = document.getElementById("viewPort"); var gl = viewPort.getContext("webgl") || viewPort.getContext("experimental-webgl"); var VERTEX_SHADER = "attribute vec4 a_Position;\n" + "attribute vec3 a_VNomal;\n" + "varying vec4 v_Position;\n" + "varying vec3 v_VNomal;\n" + "uniform mat4 u_ModelMatrix;\n" + "uniform mat4 u_ViewMatrix;\n" + "uniform mat4 u_ProjMatrix;\n" + "void main()\n" + "{\n" + " gl_Position = u_ProjMatrix*u_ViewMatrix*u_ModelMatrix*a_Position;\n" + " v_Position = a_Position;\n" + " v_VNomal = a_VNomal;\n" + "}\n"; //光线向量l不是线性插值的,必须在FragmentShader里算,所以每一个Fragment要带它所对应的vertex在空间里的位置(位置是可以插值的)。用着个位置和光源位置来算l。 var FRAGMENT_SHADER = "#ifdef GL_ES\n" + "precision mediump float;\n" + "#endif\n" + "uniform vec3 u_EyePosition;\n" + "uniform vec3 u_pointLightPosition;\n" + "varying vec4 v_Position;\n" + "varying vec3 v_VNomal;\n" + "void main()\n" + "{\n" + " vec4 pointLightColor = vec4(1.0, 1.0, 1.0, 1.0);\n" + " vec4 pointlightStrength = vec4(1.0, 1.0, 1.0, 1.0);\n" + " vec4 envLightColor = vec4(1.0, 1.0, 1.0, 1.0);\n" + " vec4 envlightStrength = vec4(0.3, 0.3, 0.3, 1.0);\n" + " vec4 matrilColor = vec4(1.0, 1.0, 1.0, 1.0);\n" + " float p = 6.0;\n" + " vec3 l = normalize(vec3(u_pointLightPosition.x - v_Position.x, u_pointLightPosition.y - v_Position.y, u_pointLightPosition.z - v_Position.z));\n" + " vec3 e = normalize(vec3(u_EyePosition.x - v_Position.x, u_EyePosition.y - v_Position.y, u_EyePosition.z - v_Position.z));\n" + " vec3 n = v_VNomal;\n" + " n = normalize(n);\n" + " float nl = dot(n, l);\n" + " if(nl<0.0) nl=0.0;\n" + " vec3 h = normalize(e+l);\n" + " float hn = dot(h, n);\n" + " gl_FragColor = matrilColor*envLightColor*envlightStrength+matrilColor*pointLightColor*pointlightStrength*nl+pointLightColor*pointlightStrength*pow(hn,p);\n" + "}\n"; /*var VERTEX_SHADER = "attribute vec4 a_Position;\n" + "uniform mat4 u_ModelMatrix;\n" + "uniform mat4 u_ViewMatrix;\n" + "uniform mat4 u_ProjMatrix;\n" + "void main()\n" + "{\n" + " gl_Position = u_ProjMatrix*u_ViewMatrix*u_ModelMatrix*a_Position;\n" + "}\n"; var FRAGMENT_SHADER = "#ifdef GL_ES\n" + "precision mediump float;\n" + "#endif\n" + "void main()\n" + "{\n" + " gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n" + "}\n";*/ var program = createProgram(gl, VERTEX_SHADER, FRAGMENT_SHADER); if(!program) { return; } gl.useProgram(program); gl.program = program; var a_Position, u_ModelMatrix, u_ViewMatrix, u_ProjMatrix, a_VNomal, u_EyePosition, u_pointLightPosition; a_Position = gl.getAttribLocation(gl.program, "a_Position"); a_VNomal = gl.getAttribLocation(gl.program, "a_VNomal"); u_ModelMatrix = gl.getUniformLocation(gl.program, "u_ModelMatrix"); u_ViewMatrix = gl.getUniformLocation(gl.program, "u_ViewMatrix"); u_ProjMatrix = gl.getUniformLocation(gl.program, "u_ProjMatrix"); u_EyePosition = gl.getUniformLocation(gl.program, "u_EyePosition"); u_pointLightPosition = gl.getUniformLocation(gl.program, "u_pointLightPosition"); if(a_Position < 0 || a_VNomal < 0 || !u_ModelMatrix || !u_ViewMatrix || !u_ProjMatrix || !u_EyePosition || !u_pointLightPosition) { alert("Failed to get store location from progrom"); return; } //The following code snippet creates a vertex buffer and binds the vertices to it var teaPotvPropertiesData =http://www.mamicode.com/ gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, teaPotvPropertiesData); //alert("bb"+teaPotData); gl.bufferData(gl.ARRAY_BUFFER, teaPotData.vertexPositions, gl.STATIC_DRAW); var VFSIZE = teaPotData.vertexPositions.BYTES_PER_ELEMENTS; gl.vertexAttribPointer(a_Position, 3, gl.FLOAT, false, VFSIZE * 3, VFSIZE * 0 ); gl.enableVertexAttribArray(a_Position); var teaPotnPropertiesData =http://www.mamicode.com/ gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, teaPotnPropertiesData); gl.bufferData(gl.ARRAY_BUFFER, teaPotData.vertexNormals, gl.STATIC_DRAW); var VNFSIZE = teaPotData.vertexNormals.BYTES_PER_ELEMENT; gl.vertexAttribPointer(a_VNomal, 3, gl.FLOAT, false, VNFSIZE * 3, VNFSIZE * 0); gl.enableVertexAttribArray(a_VNomal); //The following code snippet creates a vertex buffer and binds the indices to it teaPotPropertiesIndex = gl.createBuffer(); gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, teaPotPropertiesIndex); gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, teaPotData.indices, gl.STATIC_DRAW); var IINDEX = teaPotData.indices.length; var IFSIZE = teaPotData.indices.BYTES_PER_ELEMENT;//new Uint16Array(indices) var eyePosition = new Float32Array([0.0, 0.0, 100.0]); var pointLightPosition = new Float32Array([0.0, 0.0, 50.0]); gl.uniform3fv(u_EyePosition, eyePosition); gl.uniform3fv(u_pointLightPosition, pointLightPosition); var modelMatrix = new Matrix4(); var viewMatrix = new Matrix4(); var projMatrix = new Matrix4(); viewMatrix.setLookAt(eyePosition[0], eyePosition[1], eyePosition[2], 0.0, 0.0, 0.0, 0, 1, 0); projMatrix.setPerspective(30,viewPort.width/viewPort.height,1,100); //modelMatrix.setRotate(0, 0, 1, 0); modelMatrix.setIdentity(); //viewMatrix.setIdentity(); //projMatrix.setIdentity(); gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements); gl.uniformMatrix4fv(u_ViewMatrix, false, viewMatrix.elements); gl.uniformMatrix4fv(u_ProjMatrix, false, projMatrix.elements); gl.clearColor(0.0, 0.0, 0.0, 1.0); gl.clear(gl.COLOR_BUFFER_BIT || gl.DEPTH_BUFFER_BIT); //gl.drawArrays(gl.TRIANGLES, 0, n); gl.drawElements(gl.TRIANGLES, IINDEX, gl.UNSIGNED_SHORT, IFSIZE * 0); } function createProgram(gl, vShaderSource, fShaderSource) { var vShader = createShader(gl, gl.VERTEX_SHADER, vShaderSource); var fShader = createShader(gl, gl.FRAGMENT_SHADER, fShaderSource); if(!vShader || !fShader) { return null; } var program = gl.createProgram(); if(!program) { return null; } gl.attachShader(program, vShader); gl.attachShader(program, fShader); gl.linkProgram(program); var linked = gl.getProgramParameter(program, gl.LINK_STATUS); if(!linked) { alert("Failed to link program " + gl.getProgramInfoLog(program)); gl.deleteProgram(program); gl.deleteShader(fragmentShader); gl.deleteShader(vertexShader); return null; } return program; } function createShader(gl, type, source) { var shader = gl.createShader(type); if(!shader) { alert("Failed to create "+ type + "shader"); return null; } gl.shaderSource(shader, source); gl.compileShader(shader); var compiled = gl.getShaderParameter(shader, gl.COMPILE_STATUS); if(!compiled) { alert("Failed to compile shader " + gl.getShaderInfoLog(shader)); gl.deleteShader(shader); return null; } return shader; } </script> </body> </html>
TeaPot 用webgl画茶壶(2) Phong Shading