osg使用整理（12）：SSAO屏幕空间环境光遮蔽
2026-07-11 00:02:52 | 新服速递 | admin | 3191°c
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
}
//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 { 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::ref_ptr 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 osg::Camera::BufferComponent buffer2,osg::Texture* tex2, osg::Camera::BufferComponent buffer3,osg::Texture* tex3,int width,int height) { osg::ref_ptr 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 330 layout(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 core uniform 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 texture gPosition.xyz = fragPos.xyz; // Also store the per-fragment normals into the gbuffer gNormal = vec4(vNormal,1.0); gColor=vec4(frontCol,1.0); } )"; osg::ref_ptr osg::ref_ptr osg::ref_ptr 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 { osg::ref_ptr 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stateset auto 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 { kernelUniform->setElement(i,kernelData[i]); } ///顶点着色器 const char* vertCode=R"( #version 330 layout(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 core uniform 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 { //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 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 normals->push_back(osg::Vec3(0.0,0.0,2.f)); ///创建四边形纹理坐标 osg::ref_ptr 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 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 quadGeode->addDrawable(quad); osg::ref_ptr osg::ref_ptr osg::ref_ptr 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 { osg::ref_ptr 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stateset auto 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 330 layout(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 core uniform 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 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 normals->push_back(osg::Vec3(0.0,0.0,2.f)); ///创建四边形纹理坐标 osg::ref_ptr 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 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 quadGeode->addDrawable(quad); osg::ref_ptr osg::ref_ptr osg::ref_ptr 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);