handle negative isovalues in gpu mc

src/mol-gl/compute/marching-cubes/isosurface.ts

@@ -32,6 +32,7 @@ const IsosurfaceSchema = {
     uSize: UniformSpec('f'),
     uLevels: UniformSpec('f'),
     uCount: UniformSpec('f'),
+    uInvert: UniformSpec('b'),
 
     uGridDim: UniformSpec('v3'),
     uGridTexDim: UniformSpec('v3'),
@@ -44,7 +45,7 @@ type IsosurfaceValues = Values<typeof IsosurfaceSchema>
 
 const IsosurfaceName = 'isosurface';
 
-function getIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Texture, activeVoxelsBase: Texture, volumeData: Texture, gridDim: Vec3, gridTexDim: Vec3, transform: Mat4, isoValue: number, levels: number, scale: Vec2, count: number, packedGroup: boolean): ComputeRenderable<IsosurfaceValues> {
+function getIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Texture, activeVoxelsBase: Texture, volumeData: Texture, gridDim: Vec3, gridTexDim: Vec3, transform: Mat4, isoValue: number, levels: number, scale: Vec2, count: number, invert: boolean, packedGroup: boolean): ComputeRenderable<IsosurfaceValues> {
     if (ctx.namedComputeRenderables[IsosurfaceName]) {
         const v = ctx.namedComputeRenderables[IsosurfaceName].values as IsosurfaceValues;
 
@@ -56,6 +57,7 @@ function getIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Texture
         ValueCell.updateIfChanged(v.uSize, Math.pow(2, levels));
         ValueCell.updateIfChanged(v.uLevels, levels);
         ValueCell.updateIfChanged(v.uCount, count);
+        ValueCell.updateIfChanged(v.uInvert, invert);
 
         ValueCell.update(v.uGridDim, gridDim);
         ValueCell.update(v.uGridTexDim, gridTexDim);
@@ -66,12 +68,12 @@ function getIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Texture
 
         ctx.namedComputeRenderables[IsosurfaceName].update();
     } else {
-        ctx.namedComputeRenderables[IsosurfaceName] = createIsosurfaceRenderable(ctx, activeVoxelsPyramid, activeVoxelsBase, volumeData, gridDim, gridTexDim, transform, isoValue, levels, scale, count, packedGroup);
+        ctx.namedComputeRenderables[IsosurfaceName] = createIsosurfaceRenderable(ctx, activeVoxelsPyramid, activeVoxelsBase, volumeData, gridDim, gridTexDim, transform, isoValue, levels, scale, count, invert, packedGroup);
     }
     return ctx.namedComputeRenderables[IsosurfaceName];
 }
 
-function createIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Texture, activeVoxelsBase: Texture, volumeData: Texture, gridDim: Vec3, gridTexDim: Vec3, transform: Mat4, isoValue: number, levels: number, scale: Vec2, count: number, packedGroup: boolean) {
+function createIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Texture, activeVoxelsBase: Texture, volumeData: Texture, gridDim: Vec3, gridTexDim: Vec3, transform: Mat4, isoValue: number, levels: number, scale: Vec2, count: number, invert: boolean, packedGroup: boolean) {
     // console.log('uSize', Math.pow(2, levels))
     const values: IsosurfaceValues = {
         ...QuadValues,
@@ -85,6 +87,7 @@ function createIsosurfaceRenderable(ctx: WebGLContext, activeVoxelsPyramid: Text
         uSize: ValueCell.create(Math.pow(2, levels)),
         uLevels: ValueCell.create(levels),
         uCount: ValueCell.create(count),
+        uInvert: ValueCell.create(invert),
 
         uGridDim: ValueCell.create(gridDim),
         uGridTexDim: ValueCell.create(gridTexDim),
@@ -112,7 +115,7 @@ function setRenderingDefaults(ctx: WebGLContext) {
     state.clearColor(0, 0, 0, 0);
 }
 
-export function createIsosurfaceBuffers(ctx: WebGLContext, activeVoxelsBase: Texture, volumeData: Texture, histogramPyramid: HistogramPyramid, gridDim: Vec3, gridTexDim: Vec3, transform: Mat4, isoValue: number, packedGroup: boolean, vertexTexture?: Texture, groupTexture?: Texture, normalTexture?: Texture) {
+export function createIsosurfaceBuffers(ctx: WebGLContext, activeVoxelsBase: Texture, volumeData: Texture, histogramPyramid: HistogramPyramid, gridDim: Vec3, gridTexDim: Vec3, transform: Mat4, isoValue: number, invert: boolean, packedGroup: boolean, vertexTexture?: Texture, groupTexture?: Texture, normalTexture?: Texture) {
     const { gl, resources, extensions } = ctx;
     const { pyramidTex, height, levels, scale, count } = histogramPyramid;
     const width = pyramidTex.getWidth();
@@ -167,7 +170,7 @@ export function createIsosurfaceBuffers(ctx: WebGLContext, activeVoxelsBase: Tex
     groupTexture.attachFramebuffer(framebuffer, 1);
     normalTexture.attachFramebuffer(framebuffer, 2);
 
-    const renderable = getIsosurfaceRenderable(ctx, pyramidTex, activeVoxelsBase, volumeData, gridDim, gridTexDim, transform, isoValue, levels, scale, count, packedGroup);
+    const renderable = getIsosurfaceRenderable(ctx, pyramidTex, activeVoxelsBase, volumeData, gridDim, gridTexDim, transform, isoValue, levels, scale, count, invert, packedGroup);
     ctx.state.currentRenderItemId = -1;
 
     const { drawBuffers } = ctx.extensions;
@@ -201,7 +204,7 @@ export function createIsosurfaceBuffers(ctx: WebGLContext, activeVoxelsBase: Tex
  *
  * Implementation based on http://www.miaumiau.cat/2016/10/stream-compaction-in-webgl/
  */
-export function extractIsosurface(ctx: WebGLContext, volumeData: Texture, gridDim: Vec3, gridTexDim: Vec3, gridTexScale: Vec2, transform: Mat4, isoValue: number, packedGroup: boolean, vertexTexture?: Texture, groupTexture?: Texture, normalTexture?: Texture) {
+export function extractIsosurface(ctx: WebGLContext, volumeData: Texture, gridDim: Vec3, gridTexDim: Vec3, gridTexScale: Vec2, transform: Mat4, isoValue: number, invert: boolean, packedGroup: boolean, vertexTexture?: Texture, groupTexture?: Texture, normalTexture?: Texture) {
     // console.time('calcActiveVoxels');
     const activeVoxelsTex = calcActiveVoxels(ctx, volumeData, gridDim, gridTexDim, isoValue, gridTexScale);
     // ctx.waitForGpuCommandsCompleteSync();
@@ -213,7 +216,7 @@ export function extractIsosurface(ctx: WebGLContext, volumeData: Texture, gridDi
     // console.timeEnd('createHistogramPyramid');
 
     // console.time('createIsosurfaceBuffers');
-    const gv = createIsosurfaceBuffers(ctx, activeVoxelsTex, volumeData, compacted, gridDim, gridTexDim, transform, isoValue, packedGroup, vertexTexture, groupTexture, normalTexture);
+    const gv = createIsosurfaceBuffers(ctx, activeVoxelsTex, volumeData, compacted, gridDim, gridTexDim, transform, isoValue, invert, packedGroup, vertexTexture, groupTexture, normalTexture);
     // ctx.waitForGpuCommandsCompleteSync();
     // console.timeEnd('createIsosurfaceBuffers');
 

src/mol-gl/shader/marching-cubes/isosurface.frag.ts

@@ -18,6 +18,7 @@ uniform float uIsoValue;
 uniform float uLevels;
 uniform float uSize;
 uniform float uCount;
+uniform bool uInvert;
 
 uniform vec3 uGridDim;
 uniform vec3 uGridTexDim;
@@ -163,6 +164,13 @@ void main(void) {
     // current vertex for the up to 15 MC cases
     int currentVertex = vI - idot4(m, starts);
 
+    // ensure winding-order is the same for negative and positive iso-levels
+    if (uInvert) {
+        int v = imod(currentVertex + 1, 3);
+        if (v == 1) currentVertex += 2;
+        else if (v == 0) currentVertex -= 2;
+    }
+
     // get index into triIndices table
     int mcIndex = 16 * int(edgeIndex) + currentVertex;
     vec4 mcData = texture2D(tTriIndices, vec2(imod(mcIndex, 64), mcIndex / 64) / 64.);
@@ -273,11 +281,18 @@ void main(void) {
         voxelPadded(b1 - c3).a - voxelPadded(b1 + c3).a,
         voxelPadded(b1 - c4).a - voxelPadded(b1 + c4).a
     ));
-    mat3 normalMatrix = transpose3(inverse3(mat3(uGridTransform)));
-    gl_FragData[2].xyz = normalMatrix * -vec3(
+    gl_FragData[2].xyz = -vec3(
         n0.x + t * (n0.x - n1.x),
         n0.y + t * (n0.y - n1.y),
         n0.z + t * (n0.z - n1.z)
     );
+
+    // ensure normal-direction is the same for negative and positive iso-levels
+    if (uInvert) {
+        gl_FragData[2].xyz *= -1.0;
+    }
+
+    // apply normal matrix
+    gl_FragData[2].xyz *= transpose3(inverse3(mat3(uGridTransform)));
 }
 `;
\ No newline at end of file

src/mol-repr/structure/visual/gaussian-surface-mesh.ts

@@ -182,7 +182,7 @@ async function createGaussianSurfaceTextureMesh(ctx: VisualContext, unit: Unit,
     const isoLevel = Math.exp(-props.smoothness) / densityTextureData.radiusFactor;
 
     const buffer = textureMesh?.doubleBuffer.get();
-    const gv = extractIsosurface(ctx.webgl, densityTextureData.texture, densityTextureData.gridDim, densityTextureData.gridTexDim, densityTextureData.gridTexScale, densityTextureData.transform, isoLevel, true, buffer?.vertex, buffer?.group, buffer?.normal);
+    const gv = extractIsosurface(ctx.webgl, densityTextureData.texture, densityTextureData.gridDim, densityTextureData.gridTexDim, densityTextureData.gridTexScale, densityTextureData.transform, isoLevel, false, true, buffer?.vertex, buffer?.group, buffer?.normal);
 
     const boundingSphere = Sphere3D.expand(Sphere3D(), unit.boundary.sphere, props.radiusOffset + getStructureExtraRadius(structure));
     const surface = TextureMesh.create(gv.vertexCount, 1, gv.vertexTexture, gv.groupTexture, gv.normalTexture, boundingSphere, textureMesh);
@@ -241,7 +241,7 @@ async function createStructureGaussianSurfaceTextureMesh(ctx: VisualContext, str
     const isoLevel = Math.exp(-props.smoothness) / densityTextureData.radiusFactor;
 
     const buffer = textureMesh?.doubleBuffer.get();
-    const gv = extractIsosurface(ctx.webgl, densityTextureData.texture, densityTextureData.gridDim, densityTextureData.gridTexDim, densityTextureData.gridTexScale, densityTextureData.transform, isoLevel, true, buffer?.vertex, buffer?.group, buffer?.normal);
+    const gv = extractIsosurface(ctx.webgl, densityTextureData.texture, densityTextureData.gridDim, densityTextureData.gridTexDim, densityTextureData.gridTexScale, densityTextureData.transform, isoLevel, false, true, buffer?.vertex, buffer?.group, buffer?.normal);
 
     const boundingSphere = Sphere3D.expand(Sphere3D(), structure.boundary.sphere, props.radiusOffset + getStructureExtraRadius(structure));
     const surface = TextureMesh.create(gv.vertexCount, 1, gv.vertexTexture, gv.groupTexture, gv.normalTexture, boundingSphere, textureMesh);

src/mol-repr/volume/isosurface.ts

@@ -176,7 +176,7 @@ async function createVolumeIsosurfaceTextureMesh(ctx: VisualContext, volume: Vol
     const { texture, gridDimension, gridTexDim, gridTexScale, transform } = VolumeIsosurfaceTexture.get(volume, ctx.webgl);
 
     const buffer = textureMesh?.doubleBuffer.get();
-    const gv = extractIsosurface(ctx.webgl, texture, gridDimension, gridTexDim, gridTexScale, transform, isoLevel, false, buffer?.vertex, buffer?.group, buffer?.normal);
+    const gv = extractIsosurface(ctx.webgl, texture, gridDimension, gridTexDim, gridTexScale, transform, isoLevel, value < 0, false, buffer?.vertex, buffer?.group, buffer?.normal);
 
     const surface = TextureMesh.create(gv.vertexCount, 1, gv.vertexTexture, gv.groupTexture, gv.normalTexture, Volume.getBoundingSphere(volume), textureMesh);
 

src/tests/browser/marching-cubes.ts

@@ -73,7 +73,7 @@ async function init() {
         console.timeEnd('gpu mc pyramid2');
 
         console.time('gpu mc vert2');
-        createIsosurfaceBuffers(webgl, activeVoxelsTex2, densityTextureData2.texture, compacted2, densityTextureData2.gridDim, densityTextureData2.gridTexDim, densityTextureData2.transform, isoValue, true);
+        createIsosurfaceBuffers(webgl, activeVoxelsTex2, densityTextureData2.texture, compacted2, densityTextureData2.gridDim, densityTextureData2.gridTexDim, densityTextureData2.transform, isoValue, false, true);
         webgl.waitForGpuCommandsCompleteSync();
         console.timeEnd('gpu mc vert2');
         console.timeEnd('gpu mc2');
@@ -96,7 +96,7 @@ async function init() {
     console.timeEnd('gpu mc pyramid');
 
     console.time('gpu mc vert');
-    const gv = createIsosurfaceBuffers(webgl, activeVoxelsTex, densityTextureData.texture, compacted, densityTextureData.gridDim, densityTextureData.gridTexDim, densityTextureData.transform, isoValue, true);
+    const gv = createIsosurfaceBuffers(webgl, activeVoxelsTex, densityTextureData.texture, compacted, densityTextureData.gridDim, densityTextureData.gridTexDim, densityTextureData.transform, isoValue, false, true);
     webgl.waitForGpuCommandsCompleteSync();
     console.timeEnd('gpu mc vert');
     console.timeEnd('gpu mc');