receipt

Introduction

Once I needed to develop a system in a short time that could print a receipt. To do this, you can use the standard library "image/draw". But I always don't like to write a lot of the same type of code by hand and I tried to implement basic primitives such as "text in a rectangle", "rows" and "columns". The result is this library. Perhaps the approach that is used here does not fit into GO canons, but it does its little functionality well.

Usages

All drawing operations on the canvas are performed using the document structure description. Similar to DOM for HTML. Canvas is the main object which simply stores a link to the image and the dimensions of the work area rectangle.

    import cg "github.com/iv-menshenin/receipt"

	width := cg.Millimeters(210.0)
	height := cg.Millimeters(297.0)
	canvasRect := cg.NewRectangle(cg.ZeroPixel(), cg.ZeroPixel(), width, height)
	img := image.NewRGBA(canvasRect)
	canv := cg.NewCanvas(img, img.Rect)

In order to render the necessary information, we must parse the document into structures: rows and columns.

    pt := canv.Write(
        cg.Padding(
            cg.Millimeters(5),
            cg.Lines(
    		    cg.PaddingLeftRight(
                    cg.Millimeters(10),
                    cg.Lines(
    			        cg.Cols(
                            cg.Text(fmt.Sprintf("Order #%d %s", rand.Int(), time.Now().Format("01.02.2006 15:04")), cg.OptionAlignment(cg.AlignLeft), fontOpt),
                            cg.Text("DRAFT", cg.OptionAlignment(cg.AlignRight), fontAccentOpt),
    			        ),
    			        cg.Text("555-345-65-66 Menshenin Igor", fontOpt),
    		        )
                ),
    		    cg.FixedY(cg.Millimeters(2)),
    ...

canv.Write renders the object to the Canvas, drawing is performed sequentially - from top to bottom from left to right. The canv.Write method returns the coordinate of the bottom-right point at which drawing ended.
You can see how it works with an example.

Elements

Measurements

Three objects represent distance measures on the Canvas:

• Millimeters
• Inches
• Pixels

Lines and Columns

The two objects represent vertical and horizontal layouts on the Canvas. They are inherently containers.

• Lines
• Cols

Text

This object renders the text. It takes as arguments the text itself to be placed and options that allow you to control alignment and font.

• Text

Options:

• OptionFont
• OptionAlignment
• OptionCentered

Please note that if the text does not fit in length into the container in which it is located, then the lines will wrap by words.

Fillers and Paddings

The following structures allow you to set padding inside the container

• Padding
• PaddingLeftRight

The following structures allow you to fill a container with a void. Behavior similar to previous functions, but not containers.

• Fixed
• FixedY
• Empty

Table

The most complex (to date) structure allows you to implement the drawing of a table while maintaining the width of the columns in each row and applying fonts to all cells of the column.

• Table

Font, heading, and relative column width settings are performed by the function:

• Column

Line-by-line filling of the table with data (in text format) is performed using the following combinations of structures:

• Cols > Text
• Cols > ColSpan > Text

Example