Documentation
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Overview ¶
Package layout divides a region among the things that go in it.
It is geometry and nothing else: it decides where boxes go and hands back the views to draw them in, and it never draws. That is what lets the same rules place a widget, a string, or a hole left deliberately empty — and what keeps the sizing rules testable by asking for numbers rather than by reading a screen.
Measuring ¶
A slot whose size follows from its content says so with Measured and supplies a Measurer. The measurer is asked about the axis being divided, given how much room there is across the other one: a row of text asked how tall it is at a width, a column of labels asked how wide it is at a height. One question, either axis, which is why Measured means the same thing in Rows and in Columns.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
func Divide ¶
Divide splits total among slots, measuring against across, and returns each slot's size. The sizes always add up to at most total.
It is exported because a caller aligning something to the same grid — a header over a table, a ruler beside a pane — needs the numbers without the views.
func Rows ¶
Rows divides v into horizontal bands down the region and returns the view for each, in order.
Nothing is drawn. The caller draws into the views it is given, which is what lets a slot be left empty, be drawn conditionally, or be measured now and drawn later.
The order of business is measure, then arrange: the only order that works when one slot's size depends on its content and another's depends on what is left. Slots that end up with no height still get a view — an empty one — because a caller's draw code runs every frame, and code that only breaks when it is squeezed to nothing breaks in front of the user.
Types ¶
type Inset ¶
type Inset struct{ Top, Right, Bottom, Left int }
Inset is space held clear on each side.
func Symmetric ¶
Symmetric is one inset above and below, another to the left and right — the common case, because a terminal cell is about twice as tall as it is wide and even padding does not look even.
func (Inset) Apply ¶
Apply is what is left of r after the inset is held clear, and nothing at all when the inset is larger than the region.
The rectangle is built by hand rather than with image.Rect, which puts a backwards rectangle the right way round: an inset that overran its region would come back as a real region somewhere else instead of as no region at all.
type MeasureFunc ¶
MeasureFunc adapts a function to Measurer.
func (MeasureFunc) Measure ¶
func (f MeasureFunc) Measure(across int) int
type Measurer ¶
Measurer reports how much of one axis something wants, given how much room it has across the other.
Which axis is which is decided by whoever is asking: Rows divides height and asks for a height at a width, Columns divides width and asks for a width at a height. A type that can only answer for one axis is a type that belongs in only one of them, and saying so is the caller's business rather than this package's.
type Placement ¶
type Placement struct {
Anchor Anchor
// Width and Height are the layer's size in cells. Zero means as large as the
// space allows, less Margin.
Width, Height int
// Margin is kept clear between the layer and the edges of the space, so a layer
// anchored to a corner does not look stuck to it.
Margin int
}
Placement is where a floating layer goes in the space it floats over.
It is placement and nothing else — no drawing, no dimming, no idea what is going to be put there. Keeping it that way is what lets a hit test a frame later ask exactly the question the frame asked, and get exactly the same answer.
The layer is clamped to the space rather than allowed to hang off the edge. A dialog whose buttons are past the right margin is a dialog nobody can answer.
type Sizing ¶
type Sizing struct {
// Fixed is an exact number of rows or columns. It wins over everything else.
Fixed int
// Flex is a share of what is left after the fixed and measured slots have taken
// theirs. Two slots with flex 1 and 2 split the remainder one third to two
// thirds.
Flex int
// Measured asks the slot's [Measurer] how much it wants.
Measured bool
// Min is a floor on a flex or measured slot, so a pane cannot be squeezed into a
// size where it shows nothing useful. It is honoured while there is room for it:
// several floors can add up to more than the space there is.
Min int
// Max caps a measured slot, so content that grew without bound does not take the
// whole region.
Max int
}
Sizing says how much of an axis a slot wants.
type Slot ¶
type Slot struct {
Size Sizing
// Of is asked how much of the divided axis this slot wants, and is only
// consulted when Size says the slot is measured. A measured slot with nothing to
// ask gets its floor, which is zero unless one was set.
Of Measurer
}
Slot is one division of a region: how much room it gets, and what to ask when that follows from its content.
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