( function () {
/**
* Shaders to render 3D volumes using raycasting.
* The applied techniques are based on similar implementations in the Visvis and Vispy projects.
* This is not the only approach, therefore it's marked 1.
*/
const VolumeRenderShader1 = {
uniforms: {
'u_size': {
value: new THREE.Vector3( 1, 1, 1 )
},
'u_renderstyle': {
value: 0
},
'u_renderthreshold': {
value: 0.5
},
'u_clim': {
value: new THREE.Vector2( 1, 1 )
},
'u_data': {
value: null
},
'u_cmdata': {
value: null
}
},
vertexShader:
/* glsl */
`
varying vec4 v_nearpos;
varying vec4 v_farpos;
varying vec3 v_position;
void main() {
// Prepare transforms to map to "camera view". See also:
// https://threejs.org/docs/#api/renderers/webgl/WebGLProgram
mat4 viewtransformf = modelViewMatrix;
mat4 viewtransformi = inverse(modelViewMatrix);
// Project local vertex coordinate to camera position. Then do a step
// backward (in cam coords) to the near clipping plane, and project back. Do
// the same for the far clipping plane. This gives us all the information we
// need to calculate the ray and truncate it to the viewing cone.
vec4 position4 = vec4(position, 1.0);
vec4 pos_in_cam = viewtransformf * position4;
// Intersection of ray and near clipping plane (z = -1 in clip coords)
pos_in_cam.z = -pos_in_cam.w;
v_nearpos = viewtransformi * pos_in_cam;
// Intersection of ray and far clipping plane (z = +1 in clip coords)
pos_in_cam.z = pos_in_cam.w;
v_farpos = viewtransformi * pos_in_cam;
// Set varyings and output pos
v_position = position;
gl_Position = projectionMatrix * viewMatrix * modelMatrix * position4;
}`,
fragmentShader:
/* glsl */
`
precision highp float;
precision mediump sampler3D;
uniform vec3 u_size;
uniform int u_renderstyle;
uniform float u_renderthreshold;
uniform vec2 u_clim;
uniform sampler3D u_data;
uniform sampler2D u_cmdata;
varying vec3 v_position;
varying vec4 v_nearpos;
varying vec4 v_farpos;
// The maximum distance through our rendering volume is sqrt(3).
const int MAX_STEPS = 887; // 887 for 512^3, 1774 for 1024^3
const int REFINEMENT_STEPS = 4;
const float relative_step_size = 1.0;
const vec4 ambient_color = vec4(0.2, 0.4, 0.2, 1.0);
const vec4 diffuse_color = vec4(0.8, 0.2, 0.2, 1.0);
const vec4 specular_color = vec4(1.0, 1.0, 1.0, 1.0);
const float shininess = 40.0;
void cast_mip(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray);
void cast_iso(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray);
float sample1(vec3 texcoords);
vec4 apply_colormap(float val);
vec4 add_lighting(float val, vec3 loc, vec3 step, vec3 view_ray);
void main() {
// Normalize clipping plane info
vec3 farpos = v_farpos.xyz / v_farpos.w;
vec3 nearpos = v_nearpos.xyz / v_nearpos.w;
// Calculate unit vector pointing in the view direction through this fragment.
vec3 view_ray = normalize(nearpos.xyz - farpos.xyz);
// Compute the (negative) distance to the front surface or near clipping plane.
// v_position is the back face of the cuboid, so the initial distance calculated in the dot
// product below is the distance from near clip plane to the back of the cuboid
float distance = dot(nearpos - v_position, view_ray);
distance = max(distance, min((-0.5 - v_position.x) / view_ray.x,
(u_size.x - 0.5 - v_position.x) / view_ray.x));
distance = max(distance, min((-0.5 - v_position.y) / view_ray.y,
(u_size.y - 0.5 - v_position.y) / view_ray.y));
distance = max(distance, min((-0.5 - v_position.z) / view_ray.z,
(u_size.z - 0.5 - v_position.z) / view_ray.z));
// Now we have the starting position on the front surface
vec3 front = v_position + view_ray * distance;
// Decide how many steps to take
int nsteps = int(-distance / relative_step_size + 0.5);
if ( nsteps < 1 )
discard;
// Get starting location and step vector in texture coordinates
vec3 step = ((v_position - front) / u_size) / float(nsteps);
vec3 start_loc = front / u_size;
// For testing: show the number of steps. This helps to establish
// whether the rays are correctly oriented
//'gl_FragColor = vec4(0.0, float(nsteps) / 1.0 / u_size.x, 1.0, 1.0);
//'return;
if (u_renderstyle == 0)
cast_mip(start_loc, step, nsteps, view_ray);
else if (u_renderstyle == 1)
cast_iso(start_loc, step, nsteps, view_ray);
if (gl_FragColor.a < 0.05)
discard;
}
float sample1(vec3 texcoords) {
/* Sample float value from a 3D texture. Assumes intensity data. */
return texture(u_data, texcoords.xyz).r;
}
vec4 apply_colormap(float val) {
val = (val - u_clim[0]) / (u_clim[1] - u_clim[0]);
return texture2D(u_cmdata, vec2(val, 0.5));
}
void cast_mip(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray) {
float max_val = -1e6;
int max_i = 100;
vec3 loc = start_loc;
// Enter the raycasting loop. In WebGL 1 the loop index cannot be compared with
// non-constant expression. So we use a hard-coded max, and an additional condition
// inside the loop.
for (int iter=0; iter<MAX_STEPS; iter++) {
if (iter >= nsteps)
break;
// Sample from the 3D texture
float val = sample1(loc);
// Apply MIP operation
if (val > max_val) {
max_val = val;
max_i = iter;
}
// Advance location deeper into the volume
loc += step;
}
// Refine location, gives crispier images
vec3 iloc = start_loc + step * (float(max_i) - 0.5);
vec3 istep = step / float(REFINEMENT_STEPS);
for (int i=0; i<REFINEMENT_STEPS; i++) {
max_val = max(max_val, sample1(iloc));
iloc += istep;
}
// Resolve final color
gl_FragColor = apply_colormap(max_val);
}
void cast_iso(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray) {
gl_FragColor = vec4(0.0); // init transparent
vec4 color3 = vec4(0.0); // final color
vec3 dstep = 1.5 / u_size; // step to sample derivative
vec3 loc = start_loc;
float low_threshold = u_renderthreshold - 0.02 * (u_clim[1] - u_clim[0]);
// Enter the raycasting loop. In WebGL 1 the loop index cannot be compared with
// non-constant expression. So we use a hard-coded max, and an additional condition
// inside the loop.
for (int iter=0; iter<MAX_STEPS; iter++) {
if (iter >= nsteps)
break;
// Sample from the 3D texture
float val = sample1(loc);
if (val > low_threshold) {
// Take the last interval in smaller steps
vec3 iloc = loc - 0.5 * step;
vec3 istep = step / float(REFINEMENT_STEPS);
for (int i=0; i<REFINEMENT_STEPS; i++) {
val = sample1(iloc);
if (val > u_renderthreshold) {
gl_FragColor = add_lighting(val, iloc, dstep, view_ray);
return;
}
iloc += istep;
}
}
// Advance location deeper into the volume
loc += step;
}
}
vec4 add_lighting(float val, vec3 loc, vec3 step, vec3 view_ray)
{
// Calculate color by incorporating lighting
// View direction
vec3 V = normalize(view_ray);
// calculate normal vector from gradient
vec3 N;
float val1, val2;
val1 = sample1(loc + vec3(-step[0], 0.0, 0.0));
val2 = sample1(loc + vec3(+step[0], 0.0, 0.0));
N[0] = val1 - val2;
val = max(max(val1, val2), val);
val1 = sample1(loc + vec3(0.0, -step[1], 0.0));
val2 = sample1(loc + vec3(0.0, +step[1], 0.0));
N[1] = val1 - val2;
val = max(max(val1, val2), val);
val1 = sample1(loc + vec3(0.0, 0.0, -step[2]));
val2 = sample1(loc + vec3(0.0, 0.0, +step[2]));
N[2] = val1 - val2;
val = max(max(val1, val2), val);
float gm = length(N); // gradient magnitude
N = normalize(N);
// Flip normal so it points towards viewer
float Nselect = float(dot(N, V) > 0.0);
N = (2.0 * Nselect - 1.0) * N; // == Nselect * N - (1.0-Nselect)*N;
// Init colors
vec4 ambient_color = vec4(0.0, 0.0, 0.0, 0.0);
vec4 diffuse_color = vec4(0.0, 0.0, 0.0, 0.0);
vec4 specular_color = vec4(0.0, 0.0, 0.0, 0.0);
// note: could allow multiple lights
for (int i=0; i<1; i++)
{
// Get light direction (make sure to prevent zero devision)
vec3 L = normalize(view_ray); //lightDirs[i];
float lightEnabled = float( length(L) > 0.0 );
L = normalize(L + (1.0 - lightEnabled));
// Calculate lighting properties
float lambertTerm = clamp(dot(N, L), 0.0, 1.0);
vec3 H = normalize(L+V); // Halfway vector
float specularTerm = pow(max(dot(H, N), 0.0), shininess);
// Calculate mask
float mask1 = lightEnabled;
// Calculate colors
ambient_color += mask1 * ambient_color; // * gl_LightSource[i].ambient;
diffuse_color += mask1 * lambertTerm;
specular_color += mask1 * specularTerm * specular_color;
}
// Calculate final color by componing different components
vec4 final_color;
vec4 color = apply_colormap(val);
final_color = color * (ambient_color + diffuse_color) + specular_color;
final_color.a = color.a;
return final_color;
}`
};
THREE.VolumeRenderShader1 = VolumeRenderShader1;
} )();
