Fix artifacts when sampling AMR volume, closes #34

Author: johguenther

CHANGELOG.md

@@ -1,6 +1,10 @@
 Version History
 ---------------
 
+### Open VKL 2.0.3
+
+-   Fix artifacts when sampling AMR volume
+
 ### Open VKL 2.0.2
 
 -   Fix used element size in copyDeviceBufferToHost

openvkl/devices/cpu/volume/amr/AMRData.cpp

@@ -25,9 +25,7 @@ namespace openvkl {
         this->cellWidth = info.cellWidth;
         this->value     = *ispc(data);
         this->dims      = this->box.size() + vec3i(1);
-        // make it an ULP smaller such that floor(relBrickPos*f_dims) yields
-        // correct index even for relBrickPos=1.0f
-        this->f_dims    = nextafter(this->dims, -1);
+        this->f_dims    = vec3f(this->dims);
 
         this->worldBounds =
             box3f(vec3f(this->box.lower) * this->cellWidth,

openvkl/devices/cpu/volume/amr/CellRef.ispc

@@ -28,8 +28,10 @@ extern CellRef findCell(const AMR *uniform self,
         for (uniform int i=0;any(true);i++) {
           const AMRBrick *uniform brick = leaf->brickList[i];
           if (brick->cellWidth >= minWidth) {
-            const vec3f relBrickPos
+            vec3f relBrickPosUnclamped
               = (worldSpacePos - brick->bounds.lower) * brick->bounds_scale;
+            // clamp to 1ULP-less-1 for f_bc stay in valid index range
+            const vec3f relBrickPos = min(relBrickPosUnclamped, make_vec3f(0x1.fffffep-1f));
             // brick coords: integer cell coordinates inside brick
             // OPT: the same calculations as below, just in
             // floats. this works as long as all values we calculate
@@ -75,8 +77,10 @@ extern CellRef findLeafCell(const AMR *uniform self,
       if (isLeaf(node)) {
         const AMRLeaf *uniform leaf = &self->leaf[getOfs(node)];
         const AMRBrick *uniform brick = leaf->brickList[0];
-        const vec3f relBrickPos
+        const vec3f relBrickPosUnclamped
           = (worldSpacePos - brick->bounds.lower) * brick->bounds_scale;
+        // clamp to 1ULP-less-1 for f_bc stay in valid index range
+        const vec3f relBrickPos = min(relBrickPosUnclamped, make_vec3f(0x1.fffffep-1f));
         // brick coords: integer cell coordinates inside brick
         // OPT: the same calculations as below, just in
         // floats. this works as long as all values we calculate

openvkl/devices/gpu/compute/amr/CellRef.h

@@ -55,8 +55,11 @@ namespace ispc {
         if (isLeaf(node)) {
           const AMRLeaf *leaf   = &self->leaf[getOfs(node)];
           const AMRBrick *brick = leaf->brickList[0];
-          const vec3f relBrickPos =
+          const vec3f relBrickPosUnclamped =
               (worldSpacePos - brick->bounds.lower) * brick->bounds_scale;
+          // clamp to 1ULP-less-1 for f_bc stay in valid index range
+          const vec3f relBrickPos =
+              min(relBrickPosUnclamped, vec3f(0x1.fffffep-1f));
           // brick coords: integer cell coordinates inside brick
           // OPT: the same calculations as below, just in
           // floats. this works as long as all values we calculate