## Introduction Introduction — Introduction to libglbarcode library |

## Overview

Libglbarcode provides the core barcode functionality for glabels. It provides an intermediate barcode format, a small set of built-in barcode back-ends, and a cairo renderer. While libglbarcode does not currently include a large set of built-in barcode back-ends or renderers, its simple architecture would easily support extending its functionality beyond the needs of glabels.

## Basic Usage

    #include <libglbarcode/lgl-barcode-create.h>
    #include <libglbarcode/lgl-barcode-render-to-cairo.h>

    void
    example (gchar   *data,
             cairo_t *cr)
    {
            glBarcode *bc;

            bc = lgl_barcode_create (LGL_BARCODE_TYPE_CODE39, TRUE, FALSE, 0, 0, data);

            /* Render to cairo context.  Assume context has appropriate scale and translation.
             * Scale should be such that world units are points (1 point = 1/72 inch) and that
             * positive y values go downward.
             */
            lgl_barcode_render_to_cairo (bc, cr);

            lgl_free (bc);
    }

## Writing Renderers

The lglBarcode structure is independent of barcode type, and consists of a simple list of drawing primitives. A renderer simply traverses this list translating these primitives into native drawing commands for its target format or device. All renderers will follow this simple pattern as illustrated in the example below.

    #include <libglbarcode/lgl-barcode.h>
    #include <xxx.h>

    void
    lgl_barcode_render_to_xxx (const lglBarcode  *bc)
    {
            GList                  *p;

            lglBarcodeShape        *shape;
            lglBarcodeShapeLine    *line;
            lglBarcodeShapeBox     *box;
            lglBarcodeShapeChar    *bchar;
            lglBarcodeShapeString  *bstring;
            lglBarcodeShapeRing    *ring;
            lglBarcodeShapeHexagon *hexagon;

            for (p = bc->shapes; p != NULL; p = p->next) {

                    shape = (lglBarcodeShape *)p->data;

                    switch (shape->type)
                    {

                    case LGL_BARCODE_SHAPE_LINE:
                            line = (lglBarcodeShapeLine *) shape;

                            xxx_plot_line (line->x, line->y,
                                           line->x, line->y + line->length,
                                           line->width );
                            break;

                    case LGL_BARCODE_SHAPE_BOX:
                            box = (lglBarcodeShapeBox *) shape;

                            xxx_plot_rectangle (box->x, box->y,
                                                box->width, box->height);
                            break;

                    case LGL_BARCODE_SHAPE_CHAR:
                            bchar = (lglBarcodeShapeChar *) shape;

                            ...
                            xxx_plot_char (...);
                            break;

                    case LGL_BARCODE_SHAPE_STRING:
                            bstring = (lglBarcodeShapeString *) shape;

                            ...
                            xxx_plot_string (...);
                            break;

                    case LGL_BARCODE_SHAPE_RING:
                            ring = (lglBarcodeShapeRing *) shape;

                            ...
                            xxx_plot_circle (...);
                            break;

                    case LGL_BARCODE_SHAPE_HEXAGON:
                            hexagon = (lglBarcodeShapeHexagon *) shape;

                            ...
                            xxx_plot_polygon (...);
                            break;

                    default:
                            g_assert_not_reached ();
                            break;

                    }

            }

    }