From c7a1e0aea343d443a89395e1d981ccce8f56be27 Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Mon, 6 Jan 2025 11:03:10 -0800
Subject: [PATCH] Handle selections in the middle of ligatures too

---
 addons/addon-webgl/src/WebglRenderer.ts        | 18 ++++++++++++++++--
 .../renderer/dom/DomRendererRowFactory.ts      |  8 ++++++--
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/addons/addon-webgl/src/WebglRenderer.ts b/addons/addon-webgl/src/WebglRenderer.ts
index bd703832..aa9587aa 100644
--- a/addons/addon-webgl/src/WebglRenderer.ts
+++ b/addons/addon-webgl/src/WebglRenderer.ts
@@ -377,6 +377,8 @@ export class WebglRenderer extends Disposable implements IRenderer {
     let line: IBufferLine;
     let joinedRanges: [number, number][];
     let isJoined: boolean;
+    let skipJoinedCheckUntilX: number = 0;
+    let isValidJoinRange: boolean = true;
     let lastCharX: number;
     let range: [number, number];
     let chars: string;
@@ -405,6 +407,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
       row = y + terminal.buffer.ydisp;
       line = terminal.buffer.lines.get(row)!;
       this._model.lineLengths[y] = 0;
+      skipJoinedCheckUntilX = 0;
       joinedRanges = this._characterJoinerService.getJoinedCharacters(row);
       for (x = 0; x < terminal.cols; x++) {
         lastBg = this._cellColorResolver.result.bg;
@@ -416,17 +419,28 @@ export class WebglRenderer extends Disposable implements IRenderer {
 
         // If true, indicates that the current character(s) to draw were joined.
         isJoined = false;
+
+        // Indicates whether this cell is part of a joined range that should be ignored as it cannot
+        // be rendered entirely, like the selection state differs across the range.
+        isValidJoinRange = (x >= skipJoinedCheckUntilX);
+
         lastCharX = x;
 
         // Process any joined character ranges as needed. Because of how the
         // ranges are produced, we know that they are valid for the characters
         // and attributes of our input.
-        if (joinedRanges.length > 0 && x === joinedRanges[0][0]) {
+        if (joinedRanges.length > 0 && x === joinedRanges[0][0] && isValidJoinRange) {
           range = joinedRanges.shift()!;
 
           // If the ligature's selection state is not consistent, don't join it. This helps the
           // selection render correctly regardless whether they should be joined.
-          if (this._model.selection.isCellSelected(this._terminal, range[0], row) === this._model.selection.isCellSelected(this._terminal, range[1], row)) {
+          const firstSelectionState = this._model.selection.isCellSelected(this._terminal, range[0], row);
+          for (i = range[0] + 1; i < range[1]; i++) {
+            isValidJoinRange &&= (firstSelectionState === this._model.selection.isCellSelected(this._terminal, i, row));
+          }
+          if (!isValidJoinRange) {
+            skipJoinedCheckUntilX = range[1];
+          } else {
             isJoined = true;
 
             // We already know the exact start and end column of the joined range,
diff --git a/src/browser/renderer/dom/DomRendererRowFactory.ts b/src/browser/renderer/dom/DomRendererRowFactory.ts
index 194565f1..d5750112 100644
--- a/src/browser/renderer/dom/DomRendererRowFactory.ts
+++ b/src/browser/renderer/dom/DomRendererRowFactory.ts
@@ -84,6 +84,7 @@ export class DomRendererRowFactory {
     let charElement: HTMLSpanElement | undefined;
     let cellAmount = 0;
     let text = '';
+    let i = 0;
     let oldBg = 0;
     let oldFg = 0;
     let oldExt = 0;
@@ -122,8 +123,11 @@ export class DomRendererRowFactory {
         const range = joinedRanges.shift()!;
         // If the ligature's selection state is not consistent, don't join it. This helps the
         // selection render correctly regardless whether they should be joined.
-        if (this._isCellInSelection(range[0], row) !== this._isCellInSelection(range[1], row)) {
-          isValidJoinRange = false;
+        const firstSelectionState = this._isCellInSelection(range[0], row);
+        for (i = range[0] + 1; i < range[1]; i++) {
+          isValidJoinRange &&= (firstSelectionState === this._isCellInSelection(i, row));
+        }
+        if (!isValidJoinRange) {
           skipJoinedCheckUntilX = range[1];
         } else {
           isJoined = true;