Fix rendering for intensity range of 0

CHANGELOG.unreleased.md

@@ -25,6 +25,7 @@ For upgrade instructions, please check the [migration guide](MIGRATIONS.released
 
 ### Fixed
 - Fix that active segment and node id were not shown in status bar when being in a non-hybrid annotation. [#5638](https://github.com/scalableminds/webknossos/pull/5638)
+- Fixed that setting an intensity range of a color layer to 0 via the histogram slider led to no data being rendered at all. [#5676](https://github.com/scalableminds/webknossos/pull/5676)
 - Fix that "Compute Mesh File" button was enabled in scenarios where it should not be supported (e.g., when no segmentation layer exists). [#5648](https://github.com/scalableminds/webknossos/pull/5648)
 - Fixed a bug where an authentication error was shown when viewing the meshes tab while not logged in. [#5647](https://github.com/scalableminds/webknossos/pull/5647)
 - Fix that segment id 0 was always shown even when fallback data of the segmentation layer was visible and hovered with the mouse. [#5674](https://github.com/scalableminds/webknossos/pull/5674)

frontend/javascripts/oxalis/shaders/main_data_fragment.glsl.js

@@ -183,11 +183,15 @@ void main() {
       <% } %>
       // Keep the color in bounds of min and max
       color_value = clamp(color_value, <%= name %>_min, <%= name %>_max);
-      // Scale the color value according to the histogram settings
-      color_value = (color_value - <%= name %>_min) / (<%= name %>_max - <%= name %>_min);
+      // Scale the color value according to the histogram settings.
+      // Note: max == min would cause a division by 0. Thus we add 1 in this case and filter out the whole value below.
+      float is_max_and_min_equal = float(<%= name %>_max == <%= name %>_min);
+      color_value = (color_value - <%= name %>_min) / (<%= name %>_max - <%= name %>_min + is_max_and_min_equal);
 
       // Maybe invert the color using the inverting_factor
       color_value = abs(color_value - <%= name %>_is_inverted);
+      // Catch the case where max == min would causes a NaN value and use black as a fallback color.
+      color_value = mix(color_value, vec3(0.0), is_max_and_min_equal);
       // Multiply with color and alpha for <%= name %>
       data_color += color_value * <%= name %>_alpha * <%= name %>_color;
     }

frontend/javascripts/oxalis/view/left-border-tabs/layer_settings_tab.js

@@ -10,6 +10,7 @@ import {
   ReloadOutlined,
   ScanOutlined,
   StopOutlined,
+  WarningOutlined,
 } from "@ant-design/icons";
 import type { Dispatch } from "redux";
 import { connect } from "react-redux";
@@ -374,8 +375,10 @@ class DatasetSettings extends React.PureComponent<DatasetSettingsProps, State> {
     isInEditMode: boolean,
     layerName: string,
     elementClass: string,
+    layerSettings: DatasetLayerConfiguration,
   ) => {
     const { tracing } = this.props;
+    const { intensityRange } = layerSettings;
     const isVolumeTracing = tracing.volume != null;
     const isFallbackLayer = tracing.volume
       ? tracing.volume.fallbackLayer != null && !isColorLayer
@@ -428,6 +431,14 @@ class DatasetSettings extends React.PureComponent<DatasetSettingsProps, State> {
             <InfoCircleOutlined style={{ marginLeft: 4 }} />
           </Tooltip>
 
+          {intensityRange[0] === intensityRange[1] && !isDisabled ? (
+            <Tooltip
+              title={`No data is being rendered for this layer as the minimum and maximum of the range have the same values. 
+            If you want to hide this layer, you can also disable it with the switch on the left.`}
+            >
+              <WarningOutlined style={{ color: "var(--ant-warning)" }} />
+            </Tooltip>
+          ) : null}
           {isColorLayer ? null : this.getOptionalDownsampleVolumeIcon()}
 
           {hasHistogram ? this.getEditMinMaxButton(layerName, isInEditMode) : null}
@@ -534,6 +545,7 @@ class DatasetSettings extends React.PureComponent<DatasetSettingsProps, State> {
           isInEditMode,
           layerName,
           elementClass,
+          layerConfiguration,
         )}
         {isDisabled ? null : (
           <div style={{ marginBottom: 30, marginLeft: 10 }}>