Recover from situations where the maximum canvas size is exceeded #1928
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This is a way to detect whether a canvas exceeds the maximum dimensions if these are limited on the target device. See https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/CreatingContentforSafarioniPhone/CreatingContentforSafarioniPhone.html for limitations on iOS devices.
For performance reason, we only make the canvas bigger, but not smaller. With this change, we also make it smaller, but only when we know that its current size exceeds the maximum dimensions.
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Pull request attached. Thanks for any review. |
| @@ -46,6 +46,12 @@ ol.renderer.canvas.TileLayer = function(mapRenderer, tileLayer) { | |||
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| /** | |||
| * @private | |||
| * @type {boolean} | |||
| */ | |||
| this.canvasTooBig_; | |||
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Pull request updated. |
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Looks good to me. Please merge when Travis build passes. |
ahocevar
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Apr 3, 2014
Recover from situations where the maximum canvas size is exceeded
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| return function(context, size) { | ||
| var x = size[0] - 1; | ||
| var y = size[1] - 1; | ||
| var originalImageData = context.getImageData(x, y, 1, 1); |
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Unfortunately, this will raise security errors if not same origin or appropriate header .
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Good point. So we'll need to test the size with a canvas only made for that purpose. I'll create a pull request.
Eventually we will need a better solution than this workaround anyway, since most HiDPI devices have a limitation in canvas size that we run into.
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On HiDPI devices or displays with very high resolutions, it can happen that zooming or rotating the map exceeds the maximum possible canvas size. In such cases (at least on iPads), the map completely disappears and cannot be brought back. Until we have a better fix (e.g. canvas tiles or stripes instead of a single canvas), at least after zooming or resetting the rotation, the map should be visible again.
See https://groups.google.com/d/msg/ol3-dev/ydA_0uW7F7Q/pA4JAwCXB28J for more details on this problem.