一、基础概念
1、SSAO：通过将褶皱、孔洞和非常靠近墙面变暗的方法，近似模拟间接光照。SSAO称为屏幕空间环境光遮蔽 ，使用屏幕空间场景的深度而不是真实的几何体数据来确定遮蔽量，速度快效果好。
2、实现原理：根据物体表面法线方向生成一个半球随机深度采样，主要看物体周围深度值大小，通过这个值来确定是否被遮蔽。
3、关键点：
a. 投影采样点到屏幕空间，然后获取深度纹理
b. 采样深度缓冲
c. 如果采样位置比深度纹理深度大，说明被遮挡，遮挡系数增加
由此发现采样密度决定了最后遮蔽效果质量，但过多的采样点会导致渲染卡顿。可以通过随机旋转采样核，达到采样点少且遮蔽效果好的目的。
4、法向半球采样步骤：
a. 生成随机三维点坐标，分布类似于朝向z轴的半球
//随机数生成函数
int xorshift32()
{static usigned int x=1424447641;x^=x<<13;x^=x>>17;x^=x<<5;return x;
}float random(float min,float max)
{return min+static_cast<float>(xorshift32()/static_cast<float>(0xFFFFFFFF/(max-min)));
}
//线性插值
float lerp(float min,float max,float t)
{return min*(1.0-t)+max*t;
}
osg::Vec3f* generateHemisphereSamples(int kernelSize)
{osg::Vec3f* kernel=new osg::Vec3f[kernelSize];for (int i = 0; i < kernelSize; ++i) {kernel[i]=osg::Vec3f(random(-0.95,0.95),random(-0.95,0.95),random(0.0,1.0));kernel[i].normalize();kernel[i] *= random(0.0f, 1.0f);float scale = float(i) / float(kernelSize);scale = lerp(0.1f, 1.0f, scale * scale);kernel[i] *= scale;}return kernel;
}
b. 离散化分布点，并保证距离中心点越近，采样点越多
kernel[i] *= random(0.0f, 1.0f);
float scale = float(i) / float(kernelSize);
scale = lerp(0.1f, 1.0f, scale * scale);
kernel[i] *= scale;
c. 生成噪声纹理
osg::Vec3f* generateNoise(int noise)
{osg::Vec3f* noiseData=new osg::Vec3f[noiseSize];for(int i=0;i<noiseSize;++i){noiseData[i]=osg::Vec3f(random(-1.0,1.0),random(-1.0,1.0),0.0);noiseData[i].normalize();noiseData[i]=noiseData[i]+osg::Vec3f(1.0,1.0,1.0);noiseData[i]=noiseData[i]/2.f;}return noiseData[i];
}osg::ref_ptr<osg::Texture2D> createDataTexture(int width,int height)
{osg::ref_ptr<osg::Texture2D> texture=new osg::Texture2D;osg:Image* image=new osg:Image;auto data=generateNoise(width*height);image->setImge(width,height,1,GLRGB,GL_FLOAT,(unsigned char*)data);texture->setImage(image);texture->setWrap(osg::Texture::WRAP_S,osg::Texture::REPEAT);texture->setWrap(osg::Texture::WRAP_T,osg::Texture::REPEAT);texture->setFilter(osg::Texture::MIN_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);texture->setFilter(osg::Texture::MAG_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);return texture;
}
5、创建延迟渲染shader
/*延迟渲染相机*/
osg::ref_ptr<RttCamera> createDeferCamera(osg::Camera::BufferComponent buffer1,osg::Texture* tex1,osg::Camera::BufferComponent buffer2,osg::Texture* tex2,osg::Camera::BufferComponent buffer3,osg::Texture* tex3,int width,int height)
{osg::ref_ptr<RttCamera> camera=new RttCamera(width,height);camera->setRenderTargetImplementation(osg::Camera::RenderTargetImplementation::FRAME_BUFFER_OBJECT);camera->setClearMask(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);camera->setPostDrawCallBack(new FBOPostDrawCallback);camera->setRenderOrder(osg::Camera::PRE_RENDER,20);camera->setViewPort(0,0,width,height);if(tex1){tex1->setFilter(osg::Texture::MIN_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);tex1->setFilter(osg::Texture::MAG_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);camera->attach(buffer1,tex1);}if(tex2){tex2->setFilter(osg::Texture::MIN_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);tex2->setFilter(osg::Texture::MAG_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);camera->attach(buffer2,tex2);}if(tex3){tex3->setFilter(osg::Texture::MIN_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);tex3->setFilter(osg::Texture::MAG_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);camera->attach(buffer3,tex3);}///顶点着色器const char* vertCode=R"(#version 330layout(location = 0) in vec3 Position;layout(location = 2) in vec3 normal;layout(location = 3) in vec3 TexCoord;uniform mat4 osg_ModelViewProjectionMatrix;uniform mat4 osg_ModelViewMatrix;uniform mat4 osg_NormalMatrix;out vec3 vNormal;out vec2 texCoord;out vec4 fragPos;void main(){texCoord=TexCoord;fragPos=osg_ModelViewMatrix*vec4(Position,1.0);vec4 viewNorm=transpose(inverse(osg_ModelViewMatrix))*vec4(-normal,1.0);vNormal=normalize(viewNorm.xyz);gl_Position=osg_ModelViewProjectionMatrix*vec4(Position,1.0);})";const char* fragCode=R"(#version 330 coreuniform vec3 frontCol=vec3(1.0,0.0,0.2);layout (location = 0) out vec4 gColor;layout (location = 1) out vec4 gNormal;layout (location = 2) out vec4 gPosition;in vec2 texCoord;in vec4 fragPos;in vec3 vNormal;void main(){ // Store the fragment position vector in the first gbuffer texturegPosition.xyz = fragPos.xyz;// Also store the per-fragment normals into the gbuffergNormal = vec4(vNormal,1.0); gColor=vec4(frontCol,1.0);})";osg::ref_ptr<osg::Shader> vertShader=new osg::Shader(osg::Shader::VERTEX,vertCode);osg::ref_ptr<osg::Shader> fragShader=new osg::Shader(osg::Shader::FRAGMENT,fragCode);osg::ref_ptr<osg::Program> program=new osg::Program;program->addShader(vertShader);program->addShader(fragShader);camera->getOrCreateStateSet()->setAttributeAndModes(program,OVERRIDE_ON);return camera;
}
6、创建ssao的shader。读sampleDepth出深度缓冲区（uTexLinearDepth）。如果它在样本位置的前面，则样本位于几何图形的“内部”并有助于遮挡。如果sampleDepth在样本位置的后面，则样本不会对遮挡因子做出贡献。引入rangeCheck有助于防止较大的深度不连续性之间的错误遮挡。
osg::ref_ptr<RttCamera> createSSAOCamera(osg::Texture* postionTex,osg::Texture* normalTex,osg::Matrix& projMat,osg::Camera::BufferComponent buffer,osg::Texture* tex,int width,int height)
{osg::ref_ptr<RttCamera> camera=new RttCamera(width,height);camera->setRenderTargetImplementation(osg::Camera::RenderTargetImplementation::FRAME_BUFFER_OBJECT);camera->setClearMask(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);camera->setPostDrawCallBack(new FBOPostDrawCallback);camera->setRenderOrder(osg::Camera::PRE_RENDER,20);camera->setViewPort(0,0,width,height);if(tex){tex1->setFilter(osg::Texture::MIN_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);tex1->setFilter(osg::Texture::MAG_FILTER,osg::Texture::LINER_MIPMAP_NEAREST);camera->setViewPort(0,0,tex->getTextureWidth(),tex->getTextureHeight());camera->attach(buffer,tex);}int noise=4,kernelSize=8;float radius=5.f,power=3.f;///创建相机的statesetauto ss=camera->getOrcreateStateSet();ss->addUniform(new osg::Uniform("noiseTexture",0));ss->setTextureAttributeAndModes(0,createDatatexture(noiseSize,noiseSize));ss->addUniform(new osg::Uniform("postionTex",1));ss->setTextureAttributeAndModes(1,postionTex);ss->addUniform(new osg::Uniform("normalTex",2));ss->setTextureAttributeAndModes(2,normalTex);ss->addUniform(new osg::Uniform("ssaoRadius",radius));ss->addUniform(new osg::Uniform("ssaoPower",power));ss->addUniform(new osg::Uniform("kernelSize",kernelSize*kernelSize));ss->addUniform(new osg::Uniform("noiseTextureRcp",osg::Vec2(width/noiseSize,height/noiseSize)));ss->addUniform(new osg::Uniform("projMat",(osg::Matrixf)projMat));///创建采样半球随机数组auto kernelUniform=new osg::Uniform(osg::Uniform::FLOAT_VEC3,"ssaoKernel",kernelSize*kernelSize);auto kernelData=generateHemisphereSamples(kernelSize*kernelSize);for(int i=0;i<kernelSize*kernelSize;i++){kernelUniform->setElement(i,kernelData[i]);}///顶点着色器const char* vertCode=R"(#version 330layout(location = 0) in vec3 Position;layout(location = 3) in vec3 TexCoord;uniform mat4 osg_ModelViewProjectionMatrix;uniform mat4 osg_ModelViewMatrix;uniform mat4 osg_NormalMatrix;out vec2 texCoord;void main(){texCoord=TexCoord;gl_Position=osg_ModelViewProjectionMatrix*vec4(Position,1.0);})";///片段着色器const char* fragCode=R"(#version 330 coreuniform sampler2D positionTex;uniform sampler2D normalTex;uniform sampler2D noiseTex;const int MAX_KERNEL_SIZE=128;uniform vec3 ssaoKernel[MAX_KERNEL_SIZE];uniform mat4 projMatrix;uniform vec2 noiseTextureRep;uniform int kernelSize;uniform float ssaoRadius;uniform float ssaoPower;const float bias=0.0;void main(){ // 计算屏幕坐标系下像素点位置vec3 fragPos=texture2D(positionTex,texCoord).xyz;// 计算屏幕坐标系下的法线vec3 normal=normalize(texture2D(normalTex,texCoord).xyz);// 计算随机噪声向量vec3 rvec=texture2D(noiseTex,texCoord*noiseTextureRcp).xyz;//计算切线空间到屏幕空间转换矩阵vec3 tangent=normalize(rvec-dot(rvec,normal)*normal);vec3 bitangent=cross(tangent,normal);mat3 tbn=mat3(tangent,bitangent,normal);float occlusion=0.0;for(int i=0;i<kerSize;++i){//获取采样位置vec3 _sample=fragPos+(tbn*ssaoKernel[i])*ssaoRadius;//投影采样位置vec4 offset=projMatrix*vec4(_sample,1.0);offset.xyz/=offset.w;offset.xyz=offset.xyz*0.5+0.5;//获取采样深度float sampleDepth=texture2D(postionTex,offset.xy).z;float dist=abs(fragPos.z-sampleDepth);float rangeCheck=smoothstep(0.0,1.0,ssaoRadius/dist);occlusion+=rangeCheck*(sampleDepth>=_sample.z+bias?1.0:0.0);}occlusion=1.0-(occlusion/float(kernelSize));fragColor=vec4(vec3(occlusion),1.0);})";///创建四边形顶点osg::ref_ptr<osg:Vec3Array> vertices= new osg::Vec3Array;vertices->push_back(osg::Vec3(-width,-height,0.f));vertices->push_back(osg::Vec3(width,-height,0.f));vertices->push_back(osg::Vec3(width,height,0.f));vertices->push_back(osg::Vec3(width,-height,0.f));///创建四边形法线osg::ref_ptr<osg:Vec3Array> normals= new osg::Vec3Array;normals->push_back(osg::Vec3(0.0,0.0,2.f));///创建四边形纹理坐标osg::ref_ptr<osg:Vec2Array> texCoords= new osg::Vec2Array;texCoords->push_back(osg::Vec2(1.0,0.f));texCoords->push_back(osg::Vec2(0.0,0.f));texCoords->push_back(osg::Vec2(0.0,1.f));texCoords->push_back(osg::Vec2(1.0,1.f));///创建四边形几何osg::ref_ptr<osg:Geometry> quad= new osg::Geometry;quad->setVertexArray(vertices);quad->setNormalArray(normals);quad->setTexCoordArray(0,texCoords);quad->addPrimitiveSet(new osg::DrawArrays(GL_QUADS,0,4));///创建四边形节点osg::ref_ptr<osg::Geode> quadGeode=new osg::Geode;quadGeode->addDrawable(quad);osg::ref_ptr<osg::Shader> vertShader=new osg::Shader(osg::Shader::VERTEX,vertCode);osg::ref_ptr<osg::Shader> fragShader=new osg::Shader(osg::Shader::FRAGMENT,fragCode);osg::ref_ptr<osg::Program> program=new osg::Program;program->addShader(vertShader);program->addShader(fragShader);quadGeode->getOrCreateStateSet()->setAttributeAndModes(program,OVERRIDE_ON);camera->addChild(quadGeode);camera-》setReferenceFrame(osg::Transform::ABSOLUTE_RF);camera->setProjectionMatrix(osg::Matrix::ortho2D(widht,-width,-height,height)); return camera;
}
7、创建 blur shader 通过平均4X4周围的每个像素颜色值来避免噪声图样。
osg::ref_ptr<RttCamera> createBlurCamera(osg::Texture* colorTex,osg::Texture* ssaoTex,osg::Texture* normalTex,int width,int height)
{osg::ref_ptr<RttCamera> camera=new RttCamera(width,height);camera->setRenderTargetImplementation(osg::Camera::RenderTargetImplementation::FRAME_BUFFER_OBJECT);camera->setClearMask(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);camera->setPostDrawCallBack(new FBOPostDrawCallback);camera->setRenderOrder(osg::Camera::POST_RENDER,100);camera->setViewPort(0,0,width,height);///创建相机的statesetauto ss=camera->getOrcreateStateSet();ss->addUniform(new osg::Uniform("colorTex",0));ss->setTextureAttributeAndModes(0,colorTex);ss->addUniform(new osg::Uniform("ssaoTex",1));ss->setTextureAttributeAndModes(1,ssaoTex);ss->addUniform(new osg::Uniform("normalTex",2));ss->setTextureAttributeAndModes(2,normalTex);///顶点着色器const char* vertCode=R"(#version 330layout(location = 0) in vec3 Position;layout(location = 3) in vec3 TexCoord;uniform mat4 osg_ModelViewProjectionMatrix;uniform mat4 osg_ModelViewMatrix;uniform mat4 osg_NormalMatrix;out vec2 texCoord;void main(){texCoord=TexCoord;gl_Position=osg_ModelViewProjectionMatrix*vec4(Position,1.0);})";///片段着色器const char* fragCode=R"(#version 330 coreuniform sampler2D colorTex;uniform sampler2D ssaoTex;uniform sampler2D normalTex;const int blurSize=4;uniform mat4 osg_ModelViewMatrix;uniform float ambFactor=0.5;uniform float diffFactor=0.8;uniform float specFactor=0.15;uniform float shininess=128;vec3 calcDirLight(vec3 color,vec3 normal,float ambient,float diffuse,float specular,int strenth){float diff=max=(0,dot(normal,lightDir));float spec=pow(diff,strenth);return color*(ambient+diff*diffuse)+spec*specular;}in vec2 texCoord;out vec4 fragColor;void main(){ vec2 texelSize = 1.0 / vec2(textureSize(ssaoTex, 0));float result = 0.0;for (int i = 0; i < uBlurSize; ++i) {for (int j = 0; j < uBlurSize; ++j){vec2 offset = (vec2(-2.f) + vec2(float(x), float(y))) * texelSize;result += texture(ssaoTex, texCoord + offset).r;}}result = result / float(blurSize * blurSize);vec3 color=texture2D(colorTex,texCoord).rgb;vec3 normal=texture2D(normalTex,texCoord).rgb;vec4 viewNorm=osg_ModelViewMatrix*vec4(-normal,1.0);normal=normalize(viewNorm.xyz);vec3 lightCol=calcDirLight(color,normal,ambFactor,diffFactor,specFactor,shininess);lightCol=mix(lightCol,vec3(1.0),step(normal.z,0.0));fragCol=vec4(lightCol,1.0);})";///创建四边形顶点osg::ref_ptr<osg:Vec3Array> vertices= new osg::Vec3Array;vertices->push_back(osg::Vec3(-width,-height,0.f));vertices->push_back(osg::Vec3(width,-height,0.f));vertices->push_back(osg::Vec3(width,height,0.f));vertices->push_back(osg::Vec3(width,-height,0.f));///创建四边形法线osg::ref_ptr<osg:Vec3Array> normals= new osg::Vec3Array;normals->push_back(osg::Vec3(0.0,0.0,2.f));///创建四边形纹理坐标osg::ref_ptr<osg:Vec2Array> texCoords= new osg::Vec2Array;texCoords->push_back(osg::Vec2(1.0,0.f));texCoords->push_back(osg::Vec2(0.0,0.f));texCoords->push_back(osg::Vec2(0.0,1.f));texCoords->push_back(osg::Vec2(1.0,1.f));///创建四边形几何osg::ref_ptr<osg:Geometry> quad= new osg::Geometry;quad->setVertexArray(vertices);quad->setNormalArray(normals);quad->setTexCoordArray(0,texCoords);quad->addPrimitiveSet(new osg::DrawArrays(GL_QUADS,0,4));///创建四边形节点osg::ref_ptr<osg::Geode> quadGeode=new osg::Geode;quadGeode->addDrawable(quad);osg::ref_ptr<osg::Shader> vertShader=new osg::Shader(osg::Shader::VERTEX,vertCode);osg::ref_ptr<osg::Shader> fragShader=new osg::Shader(osg::Shader::FRAGMENT,fragCode);osg::ref_ptr<osg::Program> program=new osg::Program;program->addShader(vertShader);program->addShader(fragShader);quadGeode->getOrCreateStateSet()->setAttributeAndModes(program,OVERRIDE_ON);camera->addChild(quadGeode);camera-》setReferenceFrame(osg::Transform::ABSOLUTE_RF);camera->setProjectionMatrix(osg::Matrix::ortho2D(widht,-width,-height,height)); return camera;
}
8、将G_Buffer相机节点、ssao相机节点和模糊相机节点挂载到根节点
///首先创建延迟渲染pass,输出模型深度、颜色、法线纹理
auto positionTex=createColorTexture(width,height);
auto colorTex=createColorTexture(width,height);
auto normalTex=createColorTexture(width,height);
auto pass1=createPhongcamera(osg::Camera::COLOR_BUFFER2,positionTex, osg::Camera::COLOR_BUFFER0,colorTex,osg::Camera::COLOR_BUFFER1,normalTex,width,height);
pass1->setRenderOrder(osg::Camera::PRE_RENDER,20);
pass1->setClearColor(osg::vec4(1.0,1.0,1.0,1.0));
pass1->addChild(model);
///然后创建ssao效果pass，输出ssao纹理
auto ssaoTex=createColorTexture(width,height);
auto pass2=createSSAOCamera(positionTex,normalTex,projMat,osg::Camera::COLOR_BUFFER,ssaoTex,width,height);
pass2->setRenderOrder(osg::Camera::PRE_RENDER,100);
pass2->setClearColor(osg::vec4(1.0,1.0,1.0,1.0));
///最后创建模糊效果pass
auto pass3 =createBlurCamera(colorTex,ssaoTex,normalTex,width,height);
pass3->setRenderOrder(osg::Camera::POST_RENDER,300);
pass3->setClearColor(osg::vec4(1.0,1.0,1.0,1.0));
root->addChild(pass1);
root->addChild(pass2);
root->addChild(pass3);
