doodle/pkg/uix/canvas_cursor.go

package uix

import (
	"git.kirsle.net/apps/doodle/pkg/cursor"
	"git.kirsle.net/apps/doodle/pkg/drawtool"
	"git.kirsle.net/apps/doodle/pkg/shmem"
	"git.kirsle.net/go/render"
	"git.kirsle.net/go/ui"
)

// IsCursorOver returns true if the mouse cursor is physically over top
// of the canvas's widget space.
func (w *Canvas) IsCursorOver() bool {
	var (
		P = ui.AbsolutePosition(w)
		S = w.Size()
	)
	return shmem.Cursor.Inside(render.Rect{
		X: P.X,
		Y: P.Y,
		W: S.W,
		H: S.H,
	})
}

// presentCursor draws something at the mouse cursor on the Canvas.
//
// This is currently used in Edit Mode when you're drawing a shape with a thick
// brush size, and draws a "preview rect" under the cursor of how big a click
// will be at that size.
func (w *Canvas) presentCursor(e render.Engine) {
	// Are we to show a custom mouse cursor?
	if w.FancyCursors {
		switch w.Tool {
		case drawtool.PencilTool:
			w.cursor = cursor.NewPencil(e)
		case drawtool.FloodTool:
			w.cursor = cursor.NewFlood(e)
		default:
			w.cursor = nil
		}

		if w.IsCursorOver() && w.cursor != nil {
			cursor.Current = w.cursor
		} else {
			cursor.Current = cursor.NewPointer(e)
		}
	}

	if !w.IsCursorOver() {
		return
	}

	// Are we editing with a thick brush?
	if w.Tool == drawtool.LineTool || w.Tool == drawtool.RectTool ||
		w.Tool == drawtool.PencilTool || w.Tool == drawtool.EllipseTool ||
		w.Tool == drawtool.EraserTool {

		// Draw a box where the brush size is.
		if w.BrushSize > 0 {
			var r = w.BrushSize
			rect := render.Rect{
				X: shmem.Cursor.X - r,
				Y: shmem.Cursor.Y - r,
				W: r * 2,
				H: r * 2,
			}
			e.DrawRect(render.Black, rect)
			rect.X++
			rect.Y++
			rect.W -= 2
			rect.H -= 2
			e.DrawRect(render.RGBA(153, 153, 153, 153), rect)
		}
	}

}