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 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::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<kernelSize*kernelSize;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<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<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);