renderer.go

package glint

import (
	"context"

	"github.com/mitchellh/go-glint/flex"
)

// Renderers are responsible for helping configure layout properties and
// ultimately drawing components.
//
// Renderers may also optionally implement io.Closer. If a renderer implements
// io.Closer, the Close method will be called. After this is called. the
// Render methods will no longer be called again. This can be used to perform
// final cleanups.
type Renderer interface {
	// LayoutRoot returns the root node for the layout engine. This should
	// set any styling to restrict children such as width. If this returns nil
	// then rendering will do nothing.
	LayoutRoot() *flex.Node

	// RenderRoot is called to render the tree rooted at the given node.
	// This will always be called with the root node. In the future we plan
	// to support partial re-renders but this will be done via a separate call.
	//
	// The height of root is always greater than zero. RenderRoot won't be
	// called if the root has a zero height since this implies that nothing
	// has to be drawn.
	//
	// prev will be the previous root that was rendered. This can be used to
	// determine layout differences. This will be nil if this is the first
	// render. If the height of the previous node is zero then that means that
	// everything drawn was finalized.
	RenderRoot(root, prev *flex.Node)
}

// WithRenderer inserts the renderer into the context. This is done automatically
// by Document for components.
func WithRenderer(ctx context.Context, r Renderer) context.Context {
	return context.WithValue(ctx, rendererCtxKey, r)
}

// RendererFromContext returns the Renderer in the context or nil if no
// Renderer is found.
func RendererFromContext(ctx context.Context) Renderer {
	v, _ := ctx.Value(rendererCtxKey).(Renderer)
	return v
}

type glintCtxKey string

const (
	rendererCtxKey = glintCtxKey("renderer")
)