Cairo

Language: C

Graphics / Multimedia

Cairo was developed to provide a powerful, consistent 2D graphics API across multiple platforms. It is widely used in GUI toolkits, desktop applications, and embedded systems for rendering vector graphics and producing high-quality output.

Cairo is a 2D graphics library that supports vector graphics, including drawing shapes, text, and images. It provides high-quality rendering for multiple output targets such as screens, PDFs, SVGs, and image buffers.

Installation

linux: sudo apt install libcairo2-dev

mac: brew install cairo

windows: Download binaries from https://www.cairographics.org/download/

Usage

Cairo allows developers to draw lines, curves, shapes, text, and images on various surfaces, such as image buffers, PDFs, or windows. It supports transformations, anti-aliasing, and compositing.

Drawing a simple line on an image

#include <cairo.h>

int main() {
    cairo_surface_t *surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 200, 200);
    cairo_t *cr = cairo_create(surface);

    cairo_set_source_rgb(cr, 0, 0, 0);
    cairo_move_to(cr, 10, 10);
    cairo_line_to(cr, 190, 190);
    cairo_stroke(cr);

    cairo_surface_write_to_png(surface, "line.png");
    cairo_destroy(cr);
    cairo_surface_destroy(surface);
    return 0;
}

Creates a 200x200 image and draws a black diagonal line, saving it as `line.png`.

Drawing a rectangle

#include <cairo.h>

int main() {
    cairo_surface_t *surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 200, 200);
    cairo_t *cr = cairo_create(surface);

    cairo_set_source_rgb(cr, 1, 0, 0); // Red color
    cairo_rectangle(cr, 50, 50, 100, 100);
    cairo_fill(cr);

    cairo_surface_write_to_png(surface, "rectangle.png");
    cairo_destroy(cr);
    cairo_surface_destroy(surface);
    return 0;
}

Draws a filled red rectangle on a 200x200 image.

Drawing text

#include <cairo.h>

int main() {
    cairo_surface_t *surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 300, 100);
    cairo_t *cr = cairo_create(surface);

    cairo_select_font_face(cr, "Sans", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
    cairo_set_font_size(cr, 32);
    cairo_set_source_rgb(cr, 0, 0, 1); // Blue
    cairo_move_to(cr, 10, 50);
    cairo_show_text(cr, "Hello Cairo!");

    cairo_surface_write_to_png(surface, "text.png");
    cairo_destroy(cr);
    cairo_surface_destroy(surface);
    return 0;
}

Renders bold blue text on an image using Cairo's text functions.

Drawing a circle with transformations

#include <cairo.h>

int main() {
    cairo_surface_t *surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 200, 200);
    cairo_t *cr = cairo_create(surface);

    cairo_translate(cr, 100, 100);
    cairo_scale(cr, 1.5, 1.5);
    cairo_arc(cr, 0, 0, 50, 0, 2 * 3.14159);
    cairo_set_source_rgb(cr, 0, 1, 0); // Green
    cairo_fill(cr);

    cairo_surface_write_to_png(surface, "circle.png");
    cairo_destroy(cr);
    cairo_surface_destroy(surface);
    return 0;
}

Draws a green circle at the center of the image with scaling applied.

Exporting to PDF

#include <cairo.h>

int main() {
    cairo_surface_t *surface = cairo_pdf_surface_create("output.pdf", 400, 400);
    cairo_t *cr = cairo_create(surface);

    cairo_set_source_rgb(cr, 0, 0, 0);
    cairo_move_to(cr, 50, 50);
    cairo_line_to(cr, 350, 350);
    cairo_stroke(cr);

    cairo_destroy(cr);
    cairo_surface_destroy(surface);
    return 0;
}

Creates a PDF file and draws a line in it using Cairo.

Error Handling

CAIRO_STATUS_INVALID_SURFACE: Ensure the surface is properly created before performing drawing operations.

CAIRO_STATUS_NO_MEMORY: Check memory allocation and ensure sufficient resources for large surfaces.

CAIRO_STATUS_WRITE_ERROR: Ensure the output file path is correct and writable.

Best Practices

Always destroy the Cairo context and surface to free resources.

Use appropriate surface types (image, PDF, SVG) for your output needs.

Leverage transformations to simplify drawing operations.

Use anti-aliasing for smooth graphics.

Organize drawing code with functions to improve readability.

Official Docs Github