diff --git a/addons/addon-webgl/src/CellColorResolver.ts b/addons/addon-webgl/src/CellColorResolver.ts
index 6f61a704..afeb7245 100644
--- a/addons/addon-webgl/src/CellColorResolver.ts
+++ b/addons/addon-webgl/src/CellColorResolver.ts
@@ -42,7 +42,7 @@ export class CellColorResolver {
    * Resolves colors for the cell, putting the result into the shared {@link result}. This resolves
    * overrides, inverse and selection for the cell which can then be used to feed into the renderer.
    */
-  public resolve(cell: ICellData, x: number, y: number, deviceCellWidth: number): void {
+  public resolve(cell: ICellData, x: number, y: number, deviceCellWidth: number, deviceCellHeight: number): void {
     this.result.bg = cell.bg;
     this.result.fg = cell.fg;
     this.result.ext = cell.bg & BgFlags.HAS_EXTENDED ? cell.extended.ext : 0;
@@ -63,6 +63,11 @@ export class CellColorResolver {
       const lineWidth = Math.max(1, Math.floor(this._optionService.rawOptions.fontSize * this._coreBrowserService.dpr / 15));
       $variantOffset = x * deviceCellWidth % (Math.round(lineWidth) * 2);
     }
+    if ($variantOffset === 0) {
+      if ((code >= 0x2591 && code <= 0x2593) || (code >= 0x1FB8C && code <= 0x1FB94)) {
+        $variantOffset = ((x * deviceCellWidth) % 2) * 2 + ((y * deviceCellHeight) % 2);
+      }
+    }
 
     // Apply decorations on the bottom layer
     this._decorationService.forEachDecorationAtCell(x, y, 'bottom', d => {
diff --git a/addons/addon-webgl/src/TextureAtlas.ts b/addons/addon-webgl/src/TextureAtlas.ts
index aa0e2653..58f8da28 100644
--- a/addons/addon-webgl/src/TextureAtlas.ts
+++ b/addons/addon-webgl/src/TextureAtlas.ts
@@ -525,7 +525,8 @@ export class TextureAtlas implements ITextureAtlas {
     // Draw custom characters if applicable
     let customGlyph = false;
     if (this._config.customGlyphs !== false) {
-      customGlyph = tryDrawCustomGlyph(this._tmpCtx, chars, padding, padding, this._config.deviceCellWidth, this._config.deviceCellHeight, this._config.deviceCharWidth, this._config.deviceCharHeight, this._config.fontSize, this._config.devicePixelRatio, backgroundColor.css);
+      const variantOffset = this._workAttributeData.getUnderlineVariantOffset();
+      customGlyph = tryDrawCustomGlyph(this._tmpCtx, chars, padding, padding, this._config.deviceCellWidth, this._config.deviceCellHeight, this._config.deviceCharWidth, this._config.deviceCharHeight, this._config.fontSize, this._config.devicePixelRatio, backgroundColor.css, variantOffset);
     }
 
     // Whether to clear pixels based on a threshold difference between the glyph color and the
diff --git a/addons/addon-webgl/src/WebglRenderer.ts b/addons/addon-webgl/src/WebglRenderer.ts
index 05af6527..bd98ce60 100644
--- a/addons/addon-webgl/src/WebglRenderer.ts
+++ b/addons/addon-webgl/src/WebglRenderer.ts
@@ -478,7 +478,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
         i = ((y * terminal.cols) + x) * RENDER_MODEL_INDICIES_PER_CELL;
 
         // Load colors/resolve overrides into work colors
-        this._cellColorResolver.resolve(cell, x, row, this.dimensions.device.cell.width);
+        this._cellColorResolver.resolve(cell, x, row, this.dimensions.device.cell.width, this.dimensions.device.cell.height);
 
         // Override colors for cursor cell
         if (isCursorVisible && row === cursorY) {
diff --git a/addons/addon-webgl/src/customGlyphs/CustomGlyphRasterizer.ts b/addons/addon-webgl/src/customGlyphs/CustomGlyphRasterizer.ts
index 6302757f..08928a96 100644
--- a/addons/addon-webgl/src/customGlyphs/CustomGlyphRasterizer.ts
+++ b/addons/addon-webgl/src/customGlyphs/CustomGlyphRasterizer.ts
@@ -22,14 +22,15 @@ export function tryDrawCustomGlyph(
   deviceCharHeight: number,
   fontSize: number,
   devicePixelRatio: number,
-  backgroundColor?: string
+  backgroundColor?: string,
+  variantOffset: number = 0
 ): boolean {
   const unifiedCharDefinition = customGlyphDefinitions[c];
   if (unifiedCharDefinition) {
     // Normalize to array for uniform handling
     const parts = Array.isArray(unifiedCharDefinition) ? unifiedCharDefinition : [unifiedCharDefinition];
     for (const part of parts) {
-      drawDefinitionPart(ctx, part, xOffset, yOffset, deviceCellWidth, deviceCellHeight, deviceCharWidth, deviceCharHeight, fontSize, devicePixelRatio, backgroundColor);
+      drawDefinitionPart(ctx, part, xOffset, yOffset, deviceCellWidth, deviceCellHeight, deviceCharWidth, deviceCharHeight, fontSize, devicePixelRatio, backgroundColor, variantOffset);
     }
     return true;
   }
@@ -48,7 +49,8 @@ function drawDefinitionPart(
   deviceCharHeight: number,
   fontSize: number,
   devicePixelRatio: number,
-  backgroundColor?: string
+  backgroundColor?: string,
+  variantOffset: number = 0
 ): void {
   // Handle scaleType - adjust dimensions and offset when scaling to character area
   let drawWidth = deviceCellWidth;
@@ -74,7 +76,7 @@ function drawDefinitionPart(
       drawBlockVectorChar(ctx, part.data, drawXOffset, drawYOffset, drawWidth, drawHeight);
       break;
     case CustomGlyphDefinitionType.BLOCK_PATTERN:
-      drawPatternChar(ctx, part.data, drawXOffset, drawYOffset, drawWidth, drawHeight);
+      drawPatternChar(ctx, part.data, drawXOffset, drawYOffset, drawWidth, drawHeight, variantOffset);
       break;
     case CustomGlyphDefinitionType.PATH_FUNCTION:
       drawPathFunctionCharacter(ctx, part.data, drawXOffset, drawYOffset, drawWidth, drawHeight, devicePixelRatio, part.strokeWidth);
@@ -437,7 +439,8 @@ function drawPatternChar(
   xOffset: number,
   yOffset: number,
   deviceCellWidth: number,
-  deviceCellHeight: number
+  deviceCellHeight: number,
+  variantOffset: number = 0
 ): void {
   let patternSet = cachedPatterns.get(charDefinition);
   if (!patternSet) {
@@ -486,6 +489,15 @@ function drawPatternChar(
     pattern = throwIfFalsy(ctx.createPattern(tmpCanvas, null));
     patternSet.set(fillStyle, pattern);
   }
+  // Apply pattern offset to ensure seamless tiling across cells when cell dimensions are odd.
+  // variantOffset encodes: bit 1 = x pixel shift, bit 0 = y pixel shift.
+  const dx = (variantOffset >> 1) & 1;
+  const dy = variantOffset & 1;
+  if (dx !== 0 || dy !== 0) {
+    pattern.setTransform(new DOMMatrix().translateSelf(-dx, -dy));
+  } else {
+    pattern.setTransform(new DOMMatrix());
+  }
   ctx.fillStyle = pattern;
   ctx.fillRect(xOffset, yOffset, deviceCellWidth, deviceCellHeight);
 }