feat: interpolation in shader UI controls invlerp/transfer function and use interpolation in multi-channel setup for volume rendering

src/layer/multi_channel_setup.ts

@@ -60,11 +60,12 @@ type MakeLayerFn = (
 const MULTICHANNEL_FRAGMENT_MAIN = `#uicontrol invlerp contrast
 #uicontrol vec3 color color
 void main() {
-  float contrast_value = contrast();
   if (VOLUME_RENDERING) {
+    float contrast_value = contrast(true /* with trilinear interpolation */);
     emitRGBA(vec4(color * contrast_value, contrast_value));
   }
   else {
+    float contrast_value = contrast();
     emitRGB(color * contrast_value);
   }
 }

src/webgl/shader_ui_controls.ts

@@ -782,6 +782,15 @@ export function addControlsToBuilder(
 float ${uName}() {
   return ${uName}(getDataValue(${builderValue.channel.join(",")}));
 }
+float ${uName}(bool interpolate) {
+  if (interpolate) {
+    return ${uName}(getInterpolatedDataValue(${builderValue.channel.join(",")}));
+  }
+  else {
+    return ${uName}(getDataValue(${builderValue.channel.join(",")}));
+  }
+}
+
 `,
         ];
         builder.addFragmentCode(code);

src/widget/transfer_function.ts

@@ -1857,6 +1857,14 @@ vec4 ${name}(${shaderType} inputValue) {
 vec4 ${name}() {
   return ${name}(getDataValue(${channel.join(",")}));
 }
+vec4 ${name}(bool interpolate) {
+  if (interpolate) {
+    return ${name}(getInterpolatedDataValue(${channel.join(",")}));
+  }
+  else {
+    return ${name}(getDataValue(${channel.join(",")}));
+  }
+}
 `;
   if (dataType !== DataType.UINT64 && dataType !== DataType.FLOAT32) {
     const scalarType = DATA_TYPE_SIGNED[dataType] ? "int" : "uint";