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