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Improve RenderImage constraint solving

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We now fold the width and height properties into the constraints and try to
find a size for the image that perserves the image's intrinsict aspect ratio
while fitting within the given constraints.
This commit is contained in:
Adam Barth 2015-08-18 11:56:54 -07:00
parent 39ca4fa1ce
commit b7421fcbf1
1 changed files with 38 additions and 34 deletions
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82
packages/flutter/lib/rendering/box.dart
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@ -1395,50 +1395,54 @@ class RenderImage extends RenderBox {
}
Size _sizeForConstraints(BoxConstraints constraints) {
// Folds the given |width| and |height| into |cosntraints| so they can all
// be treated uniformly.
constraints = new BoxConstraints.tightFor(
width: _width,
height: _height
).apply(constraints);
if (constraints.isTight)
return constraints.constrain(Size.zero);
return constraints.smallest;
// If there's no image, we can't size ourselves automatically
if (_image == null) {
double width = _width == null ? 0.0 : _width;
double height = _height == null ? 0.0 : _height;
// This algorithm attempts to find a size for the RenderImage that fits in
// the given constraints and preserves the image's intrinisc aspect ratio.
// Its goals as follow:
//
// - The dimensions of the RenderImage fit within the constraints.
// - The aspect ratio of the RenderImage matches the instrinsic aspect
// ratio of the image.
// - The RenderImage's dimension are maximal subject to being smaller than
// the intrinsic size of the image.
double width = _image == null ? 0.0 : _image.width.toDouble();
double height = _image == null ? 0.0 : _image.height.toDouble();
double aspectRatio = width / height;
if (width > constraints.maxWidth) {
width = constraints.maxWidth;
height = width / aspectRatio;
}
if (height > constraints.maxHeight) {
height = constraints.maxHeight;
width = height * aspectRatio;
}
if (width < constraints.minWidth) {
width = constraints.minWidth;
height = width / aspectRatio;
}
if (height < constraints.minHeight) {
height = constraints.minHeight;
width = height * aspectRatio;
}
assert(width != null && height != null);
return constraints.constrain(new Size(width, height));
}
// If neither height nor width are specified, use inherent image
// dimensions. If only one dimension is specified, adjust the
// other dimension to maintain the aspect ratio. In both cases,
// constrain dimensions first, otherwise we end up losing the
// ratio after constraining.
if (_width == null) {
if (_height == null) {
// autosize
double width = constraints.constrainWidth(_image.width.toDouble());
double maxHeight = constraints.constrainHeight(_image.height.toDouble());
double ratio = _image.height / _image.width;
double height = width * ratio;
if (height > maxHeight) {
height = maxHeight;
width = maxHeight / ratio;
}
return constraints.constrain(new Size(width, height));
}
// Determine width from height
double width = _height * _image.width / _image.height;
return constraints.constrain(new Size(width, height));
}
if (_height == null) {
// Determine height from width
double height = _width * _image.height / _image.width;
return constraints.constrain(new Size(width, height));
}
assert(_width != null && _height != null);
return constraints.constrain(new Size(_width, _height));
}
double getMinIntrinsicWidth(BoxConstraints constraints) {
if (_width == null && _height == null)
return constraints.constrainWidth(0.0);