Add support for SGR 53, 55 overline

Specced in ECMA-48

src/browser/renderer/shared/TextureAtlas.ts

@@ -455,6 +455,7 @@ export class TextureAtlas implements ITextureAtlas {
     const italic = !!this._workAttributeData.isItalic();
     const underline = !!this._workAttributeData.isUnderline();
     const strikethrough = !!this._workAttributeData.isStrikethrough();
+    const overline = !!this._workAttributeData.isOverline();
     let fgColor = this._workAttributeData.getFgColor();
     let fgColorMode = this._workAttributeData.getFgColorMode();
     let bgColor = this._workAttributeData.getBgColor();
@@ -638,12 +639,83 @@ export class TextureAtlas implements ITextureAtlas {
       }
     }
 
+    // Overline
+    if (overline) {
+      this._tmpCtx.save();
+      const lineWidth = Math.max(1, Math.floor(this._config.fontSize * this._config.devicePixelRatio / 15));
+      // When the line width is odd, draw at a 0.5 position
+      const yOffset = lineWidth % 2 === 1 ? 0.5 : 0;
+      this._tmpCtx.lineWidth = lineWidth;
+
+      // Overline color
+      if (this._workAttributeData.isUnderlineColorDefault()) {
+        this._tmpCtx.strokeStyle = this._tmpCtx.fillStyle;
+      } else if (this._workAttributeData.isUnderlineColorRGB()) {
+        enableClearThresholdCheck = false;
+        this._tmpCtx.strokeStyle = `rgb(${AttributeData.toColorRGB(this._workAttributeData.getUnderlineColor()).join(',')})`;
+      } else {
+        enableClearThresholdCheck = false;
+        let fg = this._workAttributeData.getUnderlineColor();
+        if (this._config.drawBoldTextInBrightColors && this._workAttributeData.isBold() && fg < 8) {
+          fg += 8;
+        }
+        this._tmpCtx.strokeStyle = this._getColorFromAnsiIndex(fg).css;
+      }
+
+      // Overline style/stroke
+      this._tmpCtx.beginPath();
+      const xLeft = padding;
+      const yTop = padding + yOffset;
+      const yBot = Math.ceil(padding + lineWidth * 2) + yOffset;
+
+      for (let i = 0; i < chWidth; i++) {
+        this._tmpCtx.save();
+        const xChLeft = xLeft + i * this._config.deviceCellWidth;
+        const xChRight = xLeft + (i + 1) * this._config.deviceCellWidth;
+        this._tmpCtx.moveTo(xChLeft, yTop);
+        this._tmpCtx.lineTo(xChRight, yTop);
+        this._tmpCtx.stroke();
+        this._tmpCtx.restore();
+      }
+      this._tmpCtx.restore();
+
+      // Draw stroke in the background color for non custom characters in order to give an outline
+      // between the text and the underline. Only do this when font size is >= 12 as the underline
+      // looks odd when the font size is too small
+      if (!customGlyph && this._config.fontSize >= 12) {
+        // This only works when transparency is disabled because it's not clear how to clear stroked
+        // text
+        if (!this._config.allowTransparency && chars !== ' ') {
+          // Measure the text, only draw the stroke if there is a descent beyond an alphabetic text
+          // baseline
+          this._tmpCtx.save();
+          this._tmpCtx.textBaseline = 'alphabetic';
+          const metrics = this._tmpCtx.measureText(chars);
+          this._tmpCtx.restore();
+          if ('actualBoundingBoxDescent' in metrics && metrics.actualBoundingBoxDescent > 0) {
+            // This translates to 1/2 the line width in either direction
+            this._tmpCtx.save();
+            // Clip the region to only draw in valid pixels near the underline to avoid a slight
+            // outline around the whole glyph, as well as additional pixels in the glyph at the top
+            // which would increase GPU memory demands
+            const clipRegion = new Path2D();
+            clipRegion.rect(xLeft, yTop - Math.ceil(lineWidth / 2), this._config.deviceCellWidth * chWidth, yBot - yTop + Math.ceil(lineWidth / 2));
+            this._tmpCtx.clip(clipRegion);
+            this._tmpCtx.lineWidth = this._config.devicePixelRatio * 3;
+            this._tmpCtx.strokeStyle = backgroundColor.css;
+            this._tmpCtx.strokeText(chars, padding, padding + this._config.deviceCharHeight);
+            this._tmpCtx.restore();
+          }
+        }
+      }
+    }
+
     // Draw the character
     if (!customGlyph) {
       this._tmpCtx.fillText(chars, padding, padding + this._config.deviceCharHeight);
     }
 
-    // If this charcater is underscore and beyond the cell bounds, shift it up until it is visible
+    // If this character is underscore and beyond the cell bounds, shift it up until it is visible
     // even on the bottom row, try for a maximum of 5 pixels.
     if (chars === '_' && !this._config.allowTransparency) {
       let isBeyondCellBounds = clearColor(this._tmpCtx.getImageData(padding, padding, this._config.deviceCellWidth, this._config.deviceCellHeight), backgroundColor, foregroundColor, enableClearThresholdCheck);