ボリューム レンダリングのアルゴリズム「GPU レイ キャスティング シングル パス」を実装しています。このために、強度値の float 配列を 3D テクスチャとして使用しました (この 3D テクスチャは、球座標で規則的な 3D グリッドを記述します)。
配列値の例を次に示します。
75.839354473071637,
64.083049468866022,
65.253933716444365,
79.992431196592577,
84.411485976957096,
0.0000000000000000,
82.020319431382831,
76.808403454586994,
79.974774618246158,
0.0000000000000000,
91.127273013466336,
84.009956557448433,
90.221356094672814,
87.567422484025627,
71.940263118478072,
0.0000000000000000,
0.0000000000000000,
74.487058398181944,
..................,
..................
(完全なデータはこちら:[リンク] ( https://drive.google.com/file/d/1lbXzRucUseF-ITzFgxqeLTd0WglJJOoz/view?usp=sharing ))
球面グリッドの寸法は (r,theta,phi)=(384,15,768) で、これはロード テクスチャの入力形式です。
glTexImage3D(GL_TEXTURE_3D, 0, GL_R16F, 384, 15, 768, 0, GL_RED, GL_FLOAT, dataArray)
そして、これは私の視覚化のイメージです:
問題は、視覚化がディスク、または少なくとも同様の形式である必要があることです。
問題は、テクスチャの座標(球座標)を正しく指定していないことだと思います。
これは頂点シェーダー コードです。
#version 330 core
layout(location = 0) in vec3 vVertex; //object space vertex position
//uniform
uniform mat4 MVP; //combined modelview projection matrix
smooth out vec3 vUV; //3D texture coordinates for texture lookup in the fragment shader
void main()
{
//get the clipspace position
gl_Position = MVP*vec4(vVertex.xyz,1);
//get the 3D texture coordinates by adding (0.5,0.5,0.5) to the object space
//vertex position. Since the unit cube is at origin (min: (-0.5,-0.5,-0.5) and max: (0.5,0.5,0.5))
//adding (0.5,0.5,0.5) to the unit cube object space position gives us values from (0,0,0) to
//(1,1,1)
vUV = vVertex + vec3(0.5);
}
これはfragmenシェーダーコードです:
#version 330 core
layout(location = 0) out vec4 vFragColor; //fragment shader output
smooth in vec3 vUV; //3D texture coordinates form vertex shader
//interpolated by rasterizer
//uniforms
uniform sampler3D volume; //volume dataset
uniform vec3 camPos; //camera position
uniform vec3 step_size; //ray step size
//constants
const int MAX_SAMPLES = 300; //total samples for each ray march step
const vec3 texMin = vec3(0); //minimum texture access coordinate
const vec3 texMax = vec3(1); //maximum texture access coordinate
vec4 colour_transfer(float intensity)
{
vec3 high = vec3(100.0, 20.0, 10.0);
// vec3 low = vec3(0.0, 0.0, 0.0);
float alpha = (exp(intensity) - 1.0) / (exp(1.0) - 1.0);
return vec4(intensity * high, alpha);
}
void main()
{
//get the 3D texture coordinates for lookup into the volume dataset
vec3 dataPos = vUV;
//Getting the ray marching direction:
//get the object space position by subracting 0.5 from the
//3D texture coordinates. Then subtraact it from camera position
//and normalize to get the ray marching direction
vec3 geomDir = normalize((vUV-vec3(0.5)) - camPos);
//multiply the raymarching direction with the step size to get the
//sub-step size we need to take at each raymarching step
vec3 dirStep = geomDir * step_size;
//flag to indicate if the raymarch loop should terminate
bool stop = false;
//for all samples along the ray
for (int i = 0; i < MAX_SAMPLES; i++) {
// advance ray by dirstep
dataPos = dataPos + dirStep;
stop = dot(sign(dataPos-texMin),sign(texMax-dataPos)) < 3.0;
//if the stopping condition is true we brek out of the ray marching loop
if (stop)
break;
// data fetching from the red channel of volume texture
float sample = texture(volume, dataPos).r;
vec4 c = colour_transfer(sample);
vFragColor.rgb = c.a * c.rgb + (1 - c.a) * vFragColor.a * vFragColor.rgb;
vFragColor.a = c.a + (1 - c.a) * vFragColor.a;
//early ray termination
//if the currently composited colour alpha is already fully saturated
//we terminated the loop
if( vFragColor.a>0.99)
break;
}
}
3D テクスチャの情報を球面座標で視覚化するための座標を指定するにはどうすればよいですか?
アップデート：
頂点シェーダー:
#version 330 core
layout(location = 0) in vec3 vVertex; //object space vertex position
//uniform
uniform mat4 MVP; //combined modelview projection matrix
smooth out vec3 vUV; //3D texture coordinates for texture lookup in the fragment shader
void main()
{
//get the clipspace position
gl_Position = MVP*vec4(vVertex.xyz,1);
//get the 3D texture coordinates by adding (0.5,0.5,0.5) to the object space
//vertex position. Since the unit cube is at origin (min: (-0.5,- 0.5,-0.5) and max: (0.5,0.5,0.5))
//adding (0.5,0.5,0.5) to the unit cube object space position gives us values from (0,0,0) to
//(1,1,1)
vUV = vVertex + vec3(0.5);
}
そしてフラグメントシェーダー:
#version 330 core
#define Pi 3.1415926535897932384626433832795
layout(location = 0) out vec4 vFragColor; //fragment shader output
smooth in vec3 vUV; //3D texture coordinates form vertex shader
//interpolated by rasterizer
//uniforms
uniform sampler3D volume; //volume dataset
uniform vec3 camPos; //camera position
uniform vec3 step_size; //ray step size
//constants
const int MAX_SAMPLES = 200; //total samples for each ray march step
const vec3 texMin = vec3(0); //minimum texture access coordinate
const vec3 texMax = vec3(1); //maximum texture access coordinate
// transfer function that asigned a color and alpha from sample intensity
vec4 colour_transfer(float intensity)
{
vec3 high = vec3(100.0, 20.0, 10.0);
// vec3 low = vec3(0.0, 0.0, 0.0);
float alpha = (exp(intensity) - 1.0) / (exp(1.0) - 1.0);
return vec4(intensity * high, alpha);
}
// this function transform vector in spherical coordinates from cartesian
vec3 cart2Sphe(vec3 cart){
vec3 sphe;
sphe.x = sqrt(cart.x*cart.x+cart.y*cart.y+cart.z*cart.z);
sphe.z = atan(cart.y/cart.x);
sphe.y = atan(sqrt(cart.x*cart.x+cart.y*cart.y)/cart.z);
return sphe;
}
void main()
{
//get the 3D texture coordinates for lookup into the volume dataset
vec3 dataPos = vUV;
//Getting the ray marching direction:
//get the object space position by subracting 0.5 from the
//3D texture coordinates. Then subtraact it from camera position
//and normalize to get the ray marching direction
vec3 vec=(vUV-vec3(0.5));
vec3 spheVec=cart2Sphe(vec); // transform position to spherical
vec3 sphePos=cart2Sphe(camPos); //transform camPos to spherical
vec3 geomDir= normalize(spheVec-sphePos); // ray direction
//multiply the raymarching direction with the step size to get the
//sub-step size we need to take at each raymarching step
vec3 dirStep = geomDir * step_size ;
//flag to indicate if the raymarch loop should terminate
//for all samples along the ray
for (int i = 0; i < MAX_SAMPLES; i++) {
// advance ray by dirstep
dataPos = dataPos + dirStep;
float sample;
convert texture coordinates
vec3 spPos;
spPos.x=dataPos.x/384;
spPos.y=(dataPos.y+(Pi/2))/Pi;
spPos.z=dataPos.z/(2*Pi);
// get value from texture
sample = texture(volume,dataPos).r;
vec4 c = colour_transfer(sample)
// alpha blending function
vFragColor.rgb = c.a * c.rgb + (1 - c.a) * vFragColor.a * vFragColor.rgb;
vFragColor.a = c.a + (1 - c.a) * vFragColor.a;
if( vFragColor.a>1.0)
break;
}
// vFragColor.rgba = texture(volume,dataPos);
}
これらは、境界立方体を生成するポイントです。
glm::vec3 vertices[8] = {glm::vec3(-0.5f, -0.5f, -0.5f),
glm::vec3(0.5f, -0.5f, -0.5f),
glm::vec3(0.5f, 0.5f, -0.5f),
glm::vec3(-0.5f, 0.5f, -0.5f),
glm::vec3(-0.5f, -0.5f, 0.5f),
glm::vec3(0.5f, -0.5f, 0.5f),
glm::vec3(0.5f, 0.5f, 0.5f),
glm::vec3(-0.5f, 0.5f, 0.5f)};
//unit cube indices
GLushort cubeIndices[36] = {0, 5, 4,
5, 0, 1,
3, 7, 6,
3, 6, 2,
7, 4, 6,
6, 4, 5,
2, 1, 3,
3, 1, 0,
3, 0, 7,
7, 0, 4,
6, 5, 2,
2, 5, 1};
これは、生成された視覚化です。
