Merge pull request #6744 from SpecularAura/feature/6617_per-link-style

6617: Support Per-Link Curve Styling in Flowcharts

packages/mermaid/src/diagrams/flowchart/flowDb.spec.ts

@@ -125,4 +125,43 @@ describe('flow db getData', () => {
     const { edges } = flowDb.getData();
     expect(edges[0].curve).toBe('basis');
   });
+
+  it('should support modifying interpolate using edge id syntax', () => {
+    flowDb.addVertex('A', { text: 'A', type: 'text' }, undefined, [], [], '', {}, undefined);
+    flowDb.addVertex('B', { text: 'B', type: 'text' }, undefined, [], [], '', {}, undefined);
+    flowDb.addVertex('C', { text: 'C', type: 'text' }, undefined, [], [], '', {}, undefined);
+    flowDb.addVertex('D', { text: 'D', type: 'text' }, undefined, [], [], '', {}, undefined);
+    flowDb.addLink(['A'], ['B'], {});
+    flowDb.addLink(['A'], ['C'], { id: 'e2' });
+    flowDb.addLink(['B'], ['D'], { id: 'e3' });
+    flowDb.addLink(['C'], ['D'], {});
+    flowDb.updateLinkInterpolate(['default'], 'stepBefore');
+    flowDb.updateLinkInterpolate([0], 'basis');
+    flowDb.addVertex(
+      'e2',
+      { text: 'Shouldnt be used', type: 'text' },
+      undefined,
+      [],
+      [],
+      '',
+      {},
+      ' curve: monotoneX '
+    );
+    flowDb.addVertex(
+      'e3',
+      { text: 'Shouldnt be used', type: 'text' },
+      undefined,
+      [],
+      [],
+      '',
+      {},
+      ' curve: catmullRom '
+    );
+
+    const { edges } = flowDb.getData();
+    expect(edges[0].curve).toBe('basis');
+    expect(edges[1].curve).toBe('monotoneX');
+    expect(edges[2].curve).toBe('catmullRom');
+    expect(edges[3].curve).toBe('stepBefore');
+  });
 });

packages/mermaid/src/diagrams/flowchart/flowDb.ts

@@ -139,6 +139,9 @@ export class FlowDB implements DiagramDB {
       if (edgeDoc?.animation !== undefined) {
         edge.animation = edgeDoc.animation;
       }
+      if (edgeDoc?.curve !== undefined) {
+        edge.interpolate = edgeDoc.curve;
+      }
       return;
     }
 

packages/mermaid/src/diagrams/flowchart/parser/flow-lines.spec.js

@@ -37,6 +37,59 @@ describe('[Lines] when parsing', () => {
     expect(edges[1].interpolate).toBe('cardinal');
   });
 
+  it('should handle edge curve properties using edge ID', function () {
+    const res = flow.parser.parse(
+      'graph TD\n' +
+        'A e1@-->B\n' +
+        'A uniqueName@-->C\n' +
+        'e1@{curve: basis}\n' +
+        'uniqueName@{curve: cardinal}'
+    );
+
+    const vert = flow.parser.yy.getVertices();
+    const edges = flow.parser.yy.getEdges();
+
+    expect(edges[0].interpolate).toBe('basis');
+    expect(edges[1].interpolate).toBe('cardinal');
+  });
+
+  it('should handle edge curve properties using edge ID but without overriding default', function () {
+    const res = flow.parser.parse(
+      'graph TD\n' +
+        'A e1@-->B\n' +
+        'A-->C\n' +
+        'linkStyle default interpolate linear\n' +
+        'e1@{curve: stepAfter}'
+    );
+
+    const vert = flow.parser.yy.getVertices();
+    const edges = flow.parser.yy.getEdges();
+
+    expect(edges[0].interpolate).toBe('stepAfter');
+    expect(edges.defaultInterpolate).toBe('linear');
+  });
+
+  it('should handle edge curve properties using edge ID mixed with line interpolation', function () {
+    const res = flow.parser.parse(
+      'graph TD\n' +
+        'A e1@-->B-->D\n' +
+        'A-->C e4@-->D-->E\n' +
+        'linkStyle default interpolate linear\n' +
+        'linkStyle 1 interpolate basis\n' +
+        'e1@{curve: monotoneX}\n' +
+        'e4@{curve: stepBefore}'
+    );
+
+    const vert = flow.parser.yy.getVertices();
+    const edges = flow.parser.yy.getEdges();
+
+    expect(edges[0].interpolate).toBe('monotoneX');
+    expect(edges[1].interpolate).toBe('basis');
+    expect(edges.defaultInterpolate).toBe('linear');
+    expect(edges[3].interpolate).toBe('stepBefore');
+    expect(edges.defaultInterpolate).toBe('linear');
+  });
+
   it('should handle line interpolation multi-numbered definitions', function () {
     const res = flow.parser.parse(
       'graph TD\n' + 'A-->B\n' + 'A-->C\n' + 'linkStyle 0,1 interpolate basis'

packages/mermaid/src/docs/syntax/flowchart.md

@@ -1135,15 +1135,46 @@ It is possible to style the type of curve used for lines between items, if the d
 Available curve styles include `basis`, `bumpX`, `bumpY`, `cardinal`, `catmullRom`, `linear`, `monotoneX`, `monotoneY`,
 `natural`, `step`, `stepAfter`, and `stepBefore`.
 
+For a full list of available curves, including an explanation of custom curves, refer to
+the [Shapes](https://d3js.org/d3-shape/curve) documentation in the [d3-shape](https://github.com/d3/d3-shape/) project.
+
+Line styling can be achieved in two ways:
+
+1. Change the curve style of all the lines
+2. Change the curve style of a particular line
+
+#### Diagram level curve style
+
 In this example, a left-to-right graph uses the `stepBefore` curve style:
 
 ```
-%%{ init: { 'flowchart': { 'curve': 'stepBefore' } } }%%
+---
+config:
+  flowchart:
+    curve: stepBefore
+---
 graph LR
 ```
 
-For a full list of available curves, including an explanation of custom curves, refer to
-the [Shapes](https://d3js.org/d3-shape/curve) documentation in the [d3-shape](https://github.com/d3/d3-shape/) project.
+#### Edge level curve style using Edge IDs (v<MERMAID_RELEASE_VERSION>+)
+
+You can assign IDs to [edges](#attaching-an-id-to-edges). After assigning an ID you can modify the line style by modifying the edge's `curve` property using the following syntax:
+
+```mermaid
+flowchart LR
+    A e1@==> B
+    A e2@--> C
+    e1@{ curve: linear }
+    e2@{ curve: natural }
+```
+
+```info
+Any edge curve style modified at the edge level overrides the diagram level style.
+```
+
+```info
+If the same edge is modified multiple times the last modification will be rendered.
+```
 
 ### Styling a node
 

packages/mermaid/src/types.ts

@@ -16,6 +16,19 @@ export interface NodeMetaData {
 export interface EdgeMetaData {
   animation?: 'fast' | 'slow';
   animate?: boolean;
+  curve?:
+    | 'basis'
+    | 'bumpX'
+    | 'bumpY'
+    | 'cardinal'
+    | 'catmullRom'
+    | 'linear'
+    | 'monotoneX'
+    | 'monotoneY'
+    | 'natural'
+    | 'step'
+    | 'stepAfter'
+    | 'stepBefore';
 }
 import type { MermaidConfig } from './config.type.js';