Osg中着色器基本應用

參考資料：https://www.cnblogs.com/brainworld/p/7445290.html

https://blog.csdn.net/panda1234lee/article/details/51970893

1.首先，我們需要打開osg的渲染狀态節點osg::StateSet中對應的着色器模式。

osg::ref_ptr<osg::Program> program = new osg::Program;

mStateSet->setAttributeAndModes(program.get(),osg::StateAttribute::ON);

2.根據需要建立對應的osg着色器osg::Shader，并添加到osg::Program中。

osg::ref_ptr<osg::Shader> vertShader = new osg::Shader(osg::Shader::VERTEX, vertSource); //頂點着色器

osg::ref_ptr<osg::Shader> fragShader = new osg::Shader(osg::Shader::FRAGMENT, fragSource);//片元着色器

program->addShader(vertShader.get());

program->addShader(fragShader.get());

3.在對應的着色器中需要以字元的形式傳入着色器源碼char*  vertSource，char*  fragSource。

下面為實作Blinn-Phong光照模型例子。

//頂點着色器

static const char* vertSource = {

 //"uniform vec3 LightPosition;\n"

 "uniform vec3 EyePosition; \n"

 //varying vec2 Texcoord;

 "varying vec3 ViewDirection; \n"

 //"varying vec3 LightDirection; \n"

 "varying vec3 Normal; \n"

 "void main(void)\n"

 "{\n"

 "      gl_Position = ftransform(); \n"

          //Texcoord = gl_MultiTexCoord0.xy;

 "      vec4 OPosition = gl_ModelViewMatrix * gl_Vertex; \n"

 "      ViewDirection = EyePosition - OPosition.xyz; \n"

 //"   LightDirection = LightPosition - OPosition.xyz; \n"

 "      Normal = gl_NormalMatrix * gl_Normal; \n"

 "}\n"

};

//片元着色器

static const char* fragSource = {

"uniform vec4 LA;\n"

"uniform vec4 LD;\n"

"uniform vec4 LS;\n"

"uniform vec4 MA;\n"

"uniform vec4 MD;\n"

"uniform vec4 MS;\n"

"uniform float MfSpecularPower;\n"

"uniform vec3 LightDirection;\n"

//uniform sampler2D baseMap;

//varying vec2 Texcoord;

"varying vec3 ViewDirection;\n"

//"varying vec3 LightDirection;\n"

"varying vec3 Normal;\n"

"void main(void)\n"

"{\n"

"        vec3  LightDir = normalize(LightDirection);\n"

"        vec3  NormalDir = normalize(Normal);\n"

"        vec3  ViewDir = normalize(ViewDirection);\n"

"        vec3  HalfDir = normalize(LightDir + ViewDir);\n"

//vec3  ReDir = normalize(((2.0 * NormalDir) * fNDotL) - LightDir);

//vec4  fvBaseColor = texture2D(baseMap, Texcoord);

//

"        vec4  TotalAmbient = LA * MA;\n"

//

"        float fNDotL = dot(NormalDir, LightDir);\n"

"        vec4  TotalDiffuse = LD * MD * fNDotL;\n"

//

"        float fNDotH = max(0.0, dot(NormalDir, HalfDir));\n"

"        vec4 TotalSpecular = LS * MS * (pow(fNDotH, MfSpecularPower));\n"

//

"        gl_FragColor = (TotalAmbient + TotalDiffuse + TotalSpecular);\n"

"}\n"

};

4.在着色器源碼中定義了許多傳入參數，通過osg中osg::Uniform節點構造對應參數值并将其加入到osg::StateSet中。

//               //光照參數

//               osg::ref_ptr<osg::Uniform> LA = new osg::Uniform("LA", osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));

//               osg::ref_ptr<osg::Uniform> LD = new osg::Uniform("LD", osg::Vec4(0.6f, 0.6f, 0.6f, 1.0f));

//               osg::ref_ptr<osg::Uniform> LS = new osg::Uniform("LS", osg::Vec4(0.6f, 0.6f, 0.6f, 1.0f));

//              

//               //材質參數。

//               osg::ref_ptr<osg::Uniform> MA = new osg::Uniform("MA", mOsgcolor);

//               osg::ref_ptr<osg::Uniform> MD = new osg::Uniform("MD", mOsgcolor);

//               osg::ref_ptr<osg::Uniform> MS = new osg::Uniform("MS", osg::Vec4(0.8f, 0.8f, 0.8f, 1.0f));

//               osg::ref_ptr<osg::Uniform> MfSpecularPower = new osg::Uniform("MfSpecularPower", 90.0f);

//               mStateSet->addUniform(LA.get());

//               mStateSet->addUniform(LD.get());

//               mStateSet->addUniform(LS.get());

//               mStateSet->addUniform(MA.get());

//               mStateSet->addUniform(MD.get());

//               mStateSet->addUniform(MS.get());

//               mStateSet->addUniform(MfSpecularPower.get());