{"record":{"id":"dad18c5356f6b129","repo":"ajaxorg/ace","slug":"no-valid-mapping-found-in-256-combinations","errorCode":null,"errorMessage":"No valid mapping found in 256 combinations.","messagePattern":"No valid mapping found in 256 combinations\\.","errorType":"console","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"src/layer/font_metrics.js","lineNumber":660,"sourceCode":"            var ay = m[1] - target * mp[1];\n            \n            return [ax, ay, dx * ax, dy * ay, target * mp[2] - m[2]];\n        });\n\n        var res = solve4x4(rows);\n        var result;\n        if (res) {\n            var [x0, y0, w, h] = res;\n            if (w < 0) { x0 += w; w = -w; }\n            if (h < 0) { y0 += h; h = -h; }\n            if (validateSolution(M, x0, y0, w, h, bbox)) {\n                result = { left: x0, top: y0, width: w, height: h, right: x0 + w, bottom: y0 + h, mappingIdx: i };\n                break;\n            }\n        }\n    }\n    if (!result)\n        console.warn(\"No valid mapping found in 256 combinations.\");\n    return result;\n}\n\nvar project = (m, px, py) => {\n    var k = m[6] * px + m[7] * py + m[8];\n    return [(m[0] * px + m[1] * py + m[2]) / k, (m[3] * px + m[4] * py + m[5]) / k];\n};\n\n/**\n * Forward projects the 4 corners of the solution and checks if the \n * resulting BBox matches the input bbox.\n */\nfunction validateSolution(M, x, y, w, h, targetBbox) {\n    var  pts = [\n        [x, y], [x + w, y], [x + w, y + h], [x, y + h]\n    ];\n \n    return pts.every(p => {","sourceCodeStart":642,"sourceCodeEnd":678,"githubUrl":"https://github.com/ajaxorg/ace/blob/2c1eddc392eb92cf222a4478f1893d2b2c354fb0/src/layer/font_metrics.js#L642-L678","documentation":"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.","triggerScenarios":"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.","commonSituations":"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.","solutions":["Ensure the editor's CSS (which defines the font for .ace_editor) is loaded before the editor is created","Avoid fully overriding the editor font-family with a font that fails to load or measures to zero width","Retest in a real browser — headless environments often lack proper font metrics","Call editor.renderer.updateCharacterSize() or resize after fonts are ready (document.fonts.ready) to rerun measurement"],"exampleFix":"// before\nnew ace.Editor(...); // custom font 'Foo' not loaded, metrics fail\n// after\ndocument.fonts.ready.then(function() { editor.renderer.updateCharacterSize(); });","handlingStrategy":"validation","validationCode":"if (!result) {\n  console.warn('font metrics unavailable; falling back to default char size');\n  result = { left: 0, top: 0, width: 8, height: 16, right: 8, bottom: 16, mappingIdx: 0 };\n}","typeGuard":"function hasValidMetrics(m) { return !!m && typeof m.width === 'number' && m.width > 0 && typeof m.height === 'number' && m.height > 0; }","tryCatchPattern":"// the library only warns; guard consumers of the measurement:\nvar metrics = measure();\nif (!metrics || !(metrics.width > 0)) useDefaultCharSize();","preventionTips":["Load the editor stylesheet before instantiating the editor so fonts/CSS are ready","Wait for document.fonts.ready before measuring when using web fonts","Avoid headless environments without font rendering for metric-dependent tests","Don't set the editor font to a font that fails to load or measures at zero size"],"tags":["font-metrics","rendering","measurement","headless"],"backgroundTag":"font-metrics-measurement-failed","analyzedSha":"2c1eddc392eb92cf222a4478f1893d2b2c354fb0","analyzedAt":"2026-08-30T00:39:52.222Z","schemaVersion":2},"datasetVersion":"2026-08-30T03:17:51.788Z"}