feat(transfer-function): show data CDF in transfer function (#607)

* feat: mark transfer function as needing histogram

* feat: mark bounds for transfer function histogram

* refactor: pull histogram calculation into function

* feat: link up a transfer function CDF line shader

* fix: linting

* fix(log): correect console.log of histogram from VR

* fix: correct histogram index when invlerp and tfs are mixed

* feat: change transfer function line colours

* refactor: define CDF shader as a function

Author: seankmartin

src/volume_rendering/volume_render_layer.ts

@@ -1253,7 +1253,7 @@ outputValue = vec4(1.0, 1.0, 1.0, 1.0);
           for (let j = 0; j < 256; ++j) {
             tempBuffer2[j] = tempBuffer[j * 4];
           }
-          console.log("histogram%d", i, tempBuffer2.join(" "));
+          console.log(`histogram${i}`, tempBuffer2.join(" "));
         }
       }
       endHistogramShader();

src/webgl/shader_ui_controls.ts

@@ -1418,7 +1418,11 @@ export class ShaderControlState
       (state) => {
         const channels: HistogramChannelSpecification[] = [];
         for (const { control, trackable } of state.values()) {
-          if (control.type !== "imageInvlerp") continue;
+          if (
+            control.type !== "imageInvlerp" &&
+            control.type !== "transferFunction"
+          )
+            continue;
           channels.push({ channel: trackable.value.channel });
         }
         return channels;
@@ -1444,7 +1448,10 @@ export class ShaderControlState
     const histogramBounds = makeCachedLazyDerivedWatchableValue((state) => {
       const bounds: DataTypeInterval[] = [];
       for (const { control, trackable } of state.values()) {
-        if (control.type === "imageInvlerp") {
+        if (
+          control.type === "imageInvlerp" ||
+          control.type === "transferFunction"
+        ) {
           bounds.push(trackable.value.window);
         } else if (control.type === "propertyInvlerp") {
           const { dataType, range, window } =

src/widget/invlerp.ts

@@ -49,6 +49,7 @@ import { Uint64 } from "#src/util/uint64.js";
 import { getWheelZoomAmount } from "#src/util/wheel_zoom.js";
 import type { WatchableVisibilityPriority } from "#src/visibility_priority/frontend.js";
 import { getMemoizedBuffer } from "#src/webgl/buffer.js";
+import type { GL } from "#src/webgl/context.js";
 import type { ParameterizedEmitterDependentShaderGetter } from "#src/webgl/dynamic_shader.js";
 import { parameterizedEmitterDependentShaderGetter } from "#src/webgl/dynamic_shader.js";
 import type { HistogramSpecifications } from "#src/webgl/empirical_cdf.js";
@@ -78,6 +79,55 @@ const inputEventMap = EventActionMap.fromObject({
   "shift?+wheel": { action: "zoom-via-wheel" },
 });
 
+export function createCDFLineShader(gl: GL, textureUnit: symbol) {
+  const builder = new ShaderBuilder(gl);
+  defineLineShader(builder);
+  builder.addTextureSampler("sampler2D", "uHistogramSampler", textureUnit);
+  builder.addOutputBuffer("vec4", "out_color", 0);
+  builder.addAttribute("uint", "aDataValue");
+  builder.addUniform("float", "uBoundsFraction");
+  builder.addVertexCode(`
+float getCount(int i) {
+  return texelFetch(uHistogramSampler, ivec2(i, 0), 0).x;
+}
+vec4 getVertex(float cdf, int i) {
+  float x;
+  if (i == 0) {
+    x = -1.0;
+  } else if (i == 255) {
+    x = 1.0;
+  } else {
+    x = float(i) / 254.0 * uBoundsFraction * 2.0 - 1.0;
+  }
+  return vec4(x, cdf * (2.0 - uLineParams.y) - 1.0 + uLineParams.y * 0.5, 0.0, 1.0);
+}
+`);
+  builder.setVertexMain(`
+int lineNumber = int(aDataValue);
+int dataValue = lineNumber;
+float cumSum = 0.0;
+for (int i = 0; i <= dataValue; ++i) {
+  cumSum += getCount(i);
+}
+float total = cumSum + getCount(dataValue + 1);
+float cumSumEnd = dataValue == ${NUM_CDF_LINES - 1} ? cumSum : total;
+if (dataValue == ${NUM_CDF_LINES - 1}) {
+  cumSum + getCount(dataValue + 1);
+}
+for (int i = dataValue + 2; i < 256; ++i) {
+  total += getCount(i);
+}
+total = max(total, 1.0);
+float cdf1 = cumSum / total;
+float cdf2 = cumSumEnd / total;
+emitLine(getVertex(cdf1, lineNumber), getVertex(cdf2, lineNumber + 1), 1.0);
+`);
+  builder.setFragmentMain(`
+out_color = vec4(0.0, 1.0, 1.0, getLineAlpha());
+`);
+  return builder.build();
+}
+
 export class CdfController<
   T extends RangeAndWindowIntervals,
 > extends RefCounted {
@@ -287,7 +337,7 @@ export function getUpdatedRangeAndWindowParameters<
 // 256 bins in total.  The first and last bin are for values below the lower bound/above the upper
 // bound.
 const NUM_HISTOGRAM_BINS_IN_RANGE = 254;
-const NUM_CDF_LINES = NUM_HISTOGRAM_BINS_IN_RANGE + 1;
+export const NUM_CDF_LINES = NUM_HISTOGRAM_BINS_IN_RANGE + 1;
 
 /**
  * Panel that shows Cumulative Distribution Function (CDF) of visible data.
@@ -325,58 +375,7 @@ class CdfPanel extends IndirectRenderedPanel {
   ).value;
 
   private lineShader = this.registerDisposer(
-    (() => {
-      const builder = new ShaderBuilder(this.gl);
-      defineLineShader(builder);
-      builder.addTextureSampler(
-        "sampler2D",
-        "uHistogramSampler",
-        histogramSamplerTextureUnit,
-      );
-      builder.addOutputBuffer("vec4", "out_color", 0);
-      builder.addAttribute("uint", "aDataValue");
-      builder.addUniform("float", "uBoundsFraction");
-      builder.addVertexCode(`
-float getCount(int i) {
-  return texelFetch(uHistogramSampler, ivec2(i, 0), 0).x;
-}
-vec4 getVertex(float cdf, int i) {
-  float x;
-  if (i == 0) {
-    x = -1.0;
-  } else if (i == 255) {
-    x = 1.0;
-  } else {
-    x = float(i) / 254.0 * uBoundsFraction * 2.0 - 1.0;
-  }
-  return vec4(x, cdf * (2.0 - uLineParams.y) - 1.0 + uLineParams.y * 0.5, 0.0, 1.0);
-}
-`);
-      builder.setVertexMain(`
-int lineNumber = int(aDataValue);
-int dataValue = lineNumber;
-float cumSum = 0.0;
-for (int i = 0; i <= dataValue; ++i) {
-  cumSum += getCount(i);
-}
-float total = cumSum + getCount(dataValue + 1);
-float cumSumEnd = dataValue == ${NUM_CDF_LINES - 1} ? cumSum : total;
-if (dataValue == ${NUM_CDF_LINES - 1}) {
-  cumSum + getCount(dataValue + 1);
-}
-for (int i = dataValue + 2; i < 256; ++i) {
-  total += getCount(i);
-}
-total = max(total, 1.0);
-float cdf1 = cumSum / total;
-float cdf2 = cumSumEnd / total;
-emitLine(getVertex(cdf1, lineNumber), getVertex(cdf2, lineNumber + 1), 1.0);
-`);
-      builder.setFragmentMain(`
-out_color = vec4(0.0, 1.0, 1.0, getLineAlpha());
-`);
-      return builder.build();
-    })(),
+    (() => createCDFLineShader(this.gl, histogramSamplerTextureUnit))(),
   );
 
   private regionCornersBuffer = getSquareCornersBuffer(this.gl, 0, -1, 1, 1);

src/widget/shader_controls.ts

@@ -75,43 +75,23 @@ function getShaderLayerControlFactory<LayerType extends UserLayer>(
     case "checkbox":
       return checkboxLayerControl(() => controlState.trackable);
     case "imageInvlerp": {
-      let histogramIndex = 0;
-      for (const [
-        otherName,
-        {
-          control: { type: otherType },
-        },
-      ] of shaderControlState.state) {
-        if (otherName === controlId) break;
-        if (otherType === "imageInvlerp") ++histogramIndex;
-      }
       return channelInvlerpLayerControl(() => ({
         dataType: control.dataType,
         defaultChannel: control.default.channel,
         watchableValue: controlState.trackable,
         channelCoordinateSpaceCombiner:
           shaderControlState.channelCoordinateSpaceCombiner,
         histogramSpecifications: shaderControlState.histogramSpecifications,
-        histogramIndex,
+        histogramIndex: calculateHistogramIndex(),
         legendShaderOptions: layerShaderControls.legendShaderOptions,
       }));
     }
     case "propertyInvlerp": {
-      let histogramIndex = 0;
-      for (const [
-        otherName,
-        {
-          control: { type: otherType },
-        },
-      ] of shaderControlState.state) {
-        if (otherName === controlId) break;
-        if (otherType === "propertyInvlerp") ++histogramIndex;
-      }
       return propertyInvlerpLayerControl(() => ({
         properties: control.properties,
         watchableValue: controlState.trackable,
         histogramSpecifications: shaderControlState.histogramSpecifications,
-        histogramIndex,
+        histogramIndex: calculateHistogramIndex(),
         legendShaderOptions: layerShaderControls.legendShaderOptions,
       }));
     }
@@ -122,9 +102,40 @@ function getShaderLayerControlFactory<LayerType extends UserLayer>(
         channelCoordinateSpaceCombiner:
           shaderControlState.channelCoordinateSpaceCombiner,
         defaultChannel: control.default.channel,
+        histogramSpecifications: shaderControlState.histogramSpecifications,
+        histogramIndex: calculateHistogramIndex(),
       }));
     }
   }
+
+  function calculateHistogramIndex(controlType: string = control.type) {
+    const isMatchingControlType = (otherControlType: string) => {
+      if (
+        controlType === "imageInvlerp" ||
+        controlType === "transferFunction"
+      ) {
+        return (
+          otherControlType === "imageInvlerp" ||
+          otherControlType === "transferFunction"
+        );
+      } else if (controlType === "propertyInvlerp") {
+        return otherControlType === "propertyInvlerp";
+      } else {
+        throw new Error(`${controlType} does not support histogram index.`);
+      }
+    };
+    let histogramIndex = 0;
+    for (const [
+      otherName,
+      {
+        control: { type: otherType },
+      },
+    ] of shaderControlState.state) {
+      if (otherName === controlId) break;
+      if (isMatchingControlType(otherType)) histogramIndex++;
+    }
+    return histogramIndex;
+  }
 }
 
 function getShaderLayerControlDefinition<LayerType extends UserLayer>(