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Check fonts against two reference fonts

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In rare cases, the previous font check returned false negatives when
checking against monospace only. By checking against another font, this
can be avoided.
This commit is contained in:
Andreas Hocevar
2018-01-03 10:34:18 +01:00
parent 4fc8eff921
commit e2af5f6be3
1 changed files with 15 additions and 11 deletions
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26
src/ol/render/canvas.js
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@@ -125,22 +125,26 @@ _ol_render_canvas_.checkFont = (function() {
var retries = 60;
var checked = _ol_render_canvas_.checkedFonts_;
var labelCache = _ol_render_canvas_.labelCache;
var font = '32px monospace';
var size = '32px ';
var referenceFonts = ['monospace', 'serif'];
var len = referenceFonts.length;
var text = 'wmytzilWMYTZIL@#/&?$%10';
var interval, referenceWidth;
function isAvailable(fontFamily) {
function isAvailable(font) {
var context = _ol_render_canvas_.getMeasureContext();
context.font = font;
referenceWidth = context.measureText(text).width;
var available = true;
if (fontFamily != 'monospace') {
context.font = '32px ' + fontFamily + ',monospace';
var width = context.measureText(text).width;
// If width and referenceWidth are the same, then the 'monospace'
// fallback was used instead of the font we wanted, so the font is not
// available.
available = width != referenceWidth;
for (var i = 0; i < len; ++i) {
var referenceFont = referenceFonts[i];
context.font = size + referenceFont;
referenceWidth = context.measureText(text).width;
if (font != referenceFont) {
context.font = size + font + ',' + referenceFont;
var width = context.measureText(text).width;
// If width and referenceWidth are the same, then the fallback was used
// instead of the font we wanted, so the font is not available.
available = available && width != referenceWidth;
}
}
return available;
}