WAVE Client Renderer is a Three.js-based library for rendering a volume through Ray Casting.
Accelerated GPU Volume Ray Casting is usually implemented by multi-pass rendering.
The first pass of the shaders is very simple. It refers to the coordinates of the texture (at the coordinates of the object) the position of their rays falls on the back side of the cube.
You can find examples of GLSL shaders using the ejs templet below.
firstPass.frag
precision mediump int; precision mediump float; varying vec4 backColor; void main(void) { gl_FragColor = backColor; }
firstPass.vert
precision mediump int; precision mediump float; attribute vec4 vertColor; varying vec4 backColor; varying vec4 pos; void main(void) { backColor = vertColor; pos = projectionMatrix * modelViewMatrix * vec4(position, 1.0); gl_Position = pos; }
The second pass performs the actual data sampling and visualization of the final image.
secondPass.vert
precision mediump int; precision mediump float; attribute vec4 vertColor; varying vec4 backColor; varying vec4 pos; void main(void) { backColor = vertColor; pos = projectionMatrix * modelViewMatrix * vec4(position, 1.0); gl_Position = pos; }
secondPass.frag
#ifdef GL_FRAGMENT_PRECISION_HIGH // highp is supported precision highp int; precision highp float; #else // high is not supported precision mediump int; precision mediump float; #endif varying vec4 frontColor; varying vec4 pos; uniform sampler2D uBackCoord; uniform sampler2D uTransferFunction; uniform sampler2D uSliceMaps[<%= maxTexturesNumber %>]; uniform float uNumberOfSlices; uniform float uMinGrayVal; uniform float uMaxGrayVal; uniform float uOpacityVal; uniform float uColorVal; uniform float uAbsorptionModeIndex; uniform float uSlicesOverX; uniform float uSlicesOverY; uniform float uSteps; // uniform int uAvailable_textures_number; //Acts like a texture3D using Z slices and trilinear filtering. float getVolumeValue(vec3 volpos) { float s1Original, s2Original, s1, s2; float dx1, dy1; // float dx2, dy2; // float value; vec2 texpos1,texpos2; float slicesPerSprite = uSlicesOverX * uSlicesOverY; s1Original = floor(volpos.z*uNumberOfSlices); // s2Original = min(s1Original + 1.0, uNumberOfSlices); int tex1Index = int(floor(s1Original / slicesPerSprite)); // int tex2Index = int(floor(s2Original / slicesPerSprite)); s1 = mod(s1Original, slicesPerSprite); // s2 = mod(s2Original, slicesPerSprite); dx1 = fract(s1/uSlicesOverX); dy1 = floor(s1/uSlicesOverY)/uSlicesOverY; // dx2 = fract(s2/uSlicesOverX); // dy2 = floor(s2/uSlicesOverY)/uSlicesOverY; texpos1.x = dx1+(volpos.x/uSlicesOverX); texpos1.y = dy1+(volpos.y/uSlicesOverY); // texpos2.x = dx2+(volpos.x/uSlicesOverX); // texpos2.y = dy2+(volpos.y/uSlicesOverY); float value1 = 0.0, value2 = 0.0; // bool value1Set = false, value2Set = false; // int numberOfSlicemaps = int( ceil(uNumberOfSlices / (uSlicesOverX * uSlicesOverY)) ); <% for(var i=0; i < maxTexturesNumber; i++) { %> if( tex1Index == <%=i%> ) { value1 = texture2D(uSliceMaps[<%=i%>],texpos1).x; } <% if( i < maxTexturesNumber-1 ) { %> else <% } %> <% } %> return value1; // for (int x = 0; x < gl_MaxTextureImageUnits-2; x++) // { // if(x == numberOfSlicemaps) // { // break; // } // if(x == tex1Index) { // value1 = texture2D(uSliceMaps[x],texpos1).x; // value1Set = true; // } // if(x == tex2Index) { // value2 = texture2D(uSliceMaps[x],texpos2).x; // value2Set = true; // } // if(value1Set && value2Set) { // break; // } // } // return mix(value1, value2, fract(volpos.z*uNumberOfSlices)); } void main(void) { vec2 texC = ((pos.xy/pos.w) + 1.0) / 2.0; vec4 backColor = texture2D(uBackCoord,texC); vec3 dir = backColor.rgb - frontColor.rgb; //dir /= length(dir); vec4 vpos = frontColor; // vec3 Step = dir/uSteps; vec3 Step = dir/uSteps; vec4 accum = vec4(0, 0, 0, 0); vec4 sample = vec4(0.0, 0.0, 0.0, 0.0); vec4 colorValue = vec4(0, 0, 0, 0); float biggest_gray_value = 0.0; float opacityFactor = uOpacityVal; float lightFactor = uColorVal; // const 4095 - just example of big number // It because expression i > uSteps impossible for(float i = 0.0; i < 4095.0; i+=1.0) { // It because expression i > uSteps impossible if(i == uSteps) { break; } float gray_val = getVolumeValue(vpos.xyz); if(gray_val < uMinGrayVal || gray_val > uMaxGrayVal) { colorValue = vec4(0.0); } else { if(biggest_gray_value < gray_val) { biggest_gray_value = gray_val; } if(uAbsorptionModeIndex == 0.0) { vec2 tf_pos; tf_pos.x = (gray_val - uMinGrayVal) / (uMaxGrayVal - uMinGrayVal); tf_pos.y = 0.5; colorValue = texture2D(uTransferFunction,tf_pos); //colorValue = vec4(tf_pos.x, tf_pos.x, tf_pos.x, 1.0); sample.a = colorValue.a * opacityFactor; sample.rgb = colorValue.rgb * uColorVal; accum += sample; if(accum.a>=1.0) break; } if(uAbsorptionModeIndex == 1.0) { vec2 tf_pos; tf_pos.x = (gray_val - uMinGrayVal) / (uMaxGrayVal - uMinGrayVal); tf_pos.y = 0.5; colorValue = texture2D(uTransferFunction,tf_pos); //colorValue = vec4(tf_pos.x, tf_pos.x, tf_pos.x, 1.0); sample.a = colorValue.a * opacityFactor * (1.0 / uSteps); sample.rgb = (1.0 - accum.a) * colorValue.rgb * sample.a * lightFactor; accum += sample; if(accum.a>=1.0) break; } if(uAbsorptionModeIndex == 2.0) { vec2 tf_pos; tf_pos.x = (biggest_gray_value - uMinGrayVal) / (uMaxGrayVal - uMinGrayVal); tf_pos.y = 0.5; colorValue = texture2D(uTransferFunction,tf_pos); //colorValue = vec4(tf_pos.x, tf_pos.x, tf_pos.x, 1.0); sample.a = colorValue.a * opacityFactor; sample.rgb = colorValue.rgb * uColorVal; accum = sample; } } //advance the current position vpos.xyz += Step; //break if the position is greater than <1, 1, 1> if(vpos.x > 1.0 || vpos.y > 1.0 || vpos.z > 1.0 || vpos.x < 0.0 || vpos.y < 0.0 || vpos.z < 0.0) { break; } } gl_FragColor = accum; }