ajaxorg/ace · warning

No valid mapping found in 256 combinations.

Error message

No valid mapping found in 256 combinations.

What it means

A console.warn (not a throw) in FontMetrics when the computed-transform measurement loop exhausts all 256 candidate mappings without finding a valid character-cell measurement (result stays falsy). The function then returns undefined, which can leave glyph-position data missing downstream.

Source

Thrown at src/layer/font_metrics.js:660

            var ay = m[1] - target * mp[1];
            
            return [ax, ay, dx * ax, dy * ay, target * mp[2] - m[2]];
        });

        var res = solve4x4(rows);
        var result;
        if (res) {
            var [x0, y0, w, h] = res;
            if (w < 0) { x0 += w; w = -w; }
            if (h < 0) { y0 += h; h = -h; }
            if (validateSolution(M, x0, y0, w, h, bbox)) {
                result = { left: x0, top: y0, width: w, height: h, right: x0 + w, bottom: y0 + h, mappingIdx: i };
                break;
            }
        }
    }
    if (!result)
        console.warn("No valid mapping found in 256 combinations.");
    return result;
}

var project = (m, px, py) => {
    var k = m[6] * px + m[7] * py + m[8];
    return [(m[0] * px + m[1] * py + m[2]) / k, (m[3] * px + m[4] * py + m[5]) / k];
};

/**
 * Forward projects the 4 corners of the solution and checks if the 
 * resulting BBox matches the input bbox.
 */
function validateSolution(M, x, y, w, h, targetBbox) {
    var  pts = [
        [x, y], [x + w, y], [x + w, y + h], [x, y + h]
    ];
 
    return pts.every(p => {

View on GitHub (pinned to 2c1eddc392)

Solutions

1. Ensure the editor's CSS (which defines the font for .ace_editor) is loaded before the editor is created
2. Avoid fully overriding the editor font-family with a font that fails to load or measures to zero width
3. Retest in a real browser — headless environments often lack proper font metrics
4. Call editor.renderer.updateCharacterSize() or resize after fonts are ready (document.fonts.ready) to rerun measurement

Example fix

// before
new ace.Editor(...); // custom font 'Foo' not loaded, metrics fail
// after
document.fonts.ready.then(function() { editor.renderer.updateCharacterSize(); });

if (!result) {
  console.warn('font metrics unavailable; falling back to default char size');
  result = { left: 0, top: 0, width: 8, height: 16, right: 8, bottom: 16, mappingIdx: 0 };
}

function hasValidMetrics(m) { return !!m && typeof m.width === 'number' && m.width > 0 && typeof m.height === 'number' && m.height > 0; }

// the library only warns; guard consumers of the measurement:
var metrics = measure();
if (!metrics || !(metrics.width > 0)) useDefaultCharSize();

When it happens

Trigger: Measuring $renderChar... under unusual rendering environments: headless browsers, exotic zoom levels, fonts that fail to load, or canvas/DOM measurement APIs returning degenerate values so every tested mapping fails.

Common situations: CI/headless screenshot tests without real font rendering; zoom/scale combinations in Electron or high-DPI setups; custom CSS overriding the editor's font so measurement characters have zero size.

AI-assisted analysis of ajaxorg/ace@2c1eddc392 (2026-08-30). Data as JSON: /api/errors/dad18c5356f6b129. Report an issue: GitHub.