7、基于osg引擎实现读取vtk数据通过着色器实现简单体渲染(1)

1、顶点着色器代码

#version 110
/* GLSL 1.10需要显式声明精度 (OpenGL ES要求) */
#ifdef GL_ES
precision highp  float;
#endif
// 体数据采样步长
uniform float xStepSize,yStepSize,zStepSize;
// 体数据纹理和颜色纹理
uniform sampler3D baseTexture;
uniform sampler1D tfTexture;
// 体数据包围盒边界
uniform vec3 minBound,maxBound;
varying vec3 vDirection;//模型空间下的光线方向
varying vec3 vCameraModelPosition;//模型空间下的相机位置
void main(void)
{// 计算裁剪空间的位置gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;vec4 cameraPos = (gl_ModelViewMatrixInverse * vec4(0, 0, 0, 1));vCameraModelPosition = cameraPos.xyz/cameraPos.w;vDirection = gl_Vertex.xyz/gl_Vertex.w- vCameraModelPosition;}

2、片元着色器代码

#version 110
/* GLSL 1.10需要显式声明精度 (OpenGL ES要求) */
#ifdef GL_ES
precision highp  float;
precision highp sampler3D;
precision highp sampler1D;
#endif
#define EPSILON 1e-3// 体数据纹理和颜色纹理
uniform sampler3D baseTexture;
uniform sampler1D tfTexture;uniform int steps;//采样步长，值越大，采样次数越多，效果越小，但性能越差
uniform float densityFactor;//值越大，颜色变化剧烈，细节边界变得锐利，可能出现不平滑的锯齿状过渡；值越小，颜色变化缓慢，叠加的颜色较多，导致整体视觉上更加柔和、模糊，增强了雾气感
// 体数据包围盒边界
uniform vec3 minBound,maxBound;varying vec3 vDirection;//模型空间下的光线方向
varying vec3 vCameraModelPosition;//模型空间下的相机位置const int maxSamples = 256;
vec2 hitBox(vec3 orig, vec3 dir) {vec3 inv_dir = 1.0 / dir;// 光线方向倒数（处理正负方向）vec3 tmin_tmp = (minBound - orig) * inv_dir;// 沿光线方向到达包围盒各轴最小边界的距离vec3 tmax_tmp = (maxBound - orig) * inv_dir; // 沿光线方向到达包围盒各轴最大边界的距离vec3 tmin = min(tmin_tmp, tmax_tmp);// 各轴向的最近交点vec3 tmax = max(tmin_tmp, tmax_tmp);// 各轴向的最远交点float near = max(max(tmin.x, max(tmin.y, tmin.z)),0.0);// 光线最终进入包围盒的距离float far = min(tmax.x, min( tmax.y, tmax.z)); // 光线最终离开包围盒的距离return vec2( near, far );
}void main(void)
{vec3 rayDir = normalize(vDirection);vec2 bounds = hitBox( vCameraModelPosition, rayDir );bounds.x -= 0.000001;if ( bounds.x >= bounds.y) discard;//光线与包围盒无交点。vec3 sampleStart = vCameraModelPosition + bounds.x * rayDir;// 初始化颜色累积vec4 finalColor = vec4(0.0);const float opacityThreshold = 0.99;   // 不透明度阈值float T = 1.0;// 光线步进采样float delta = sqrt(3.0) / float(steps);             // 均匀步长vec3 voxelSizeInv = 1.0 / (maxBound - minBound); for (float t = bounds.x; t < bounds.y; t += delta) {sampleStart = vCameraModelPosition + t * rayDir;vec3 texCoord = (sampleStart - minBound) * voxelSizeInv;float density = texture3D(baseTexture, texCoord).r;vec4 color = texture1D(tfTexture, density);color.rbg = pow(color.rbg, vec3(2.2));//从gamma空间转换到线性空间color *= densityFactor * delta;finalColor += T*color;T*=1.0-color.a;if (T<0.01) break;}// 丢弃完全透明的片元if (finalColor.a < EPSILON) discard;finalColor.rgb = pow(finalColor.rgb, vec3(1.0/2.2));gl_FragColor = finalColor;}