https://cairographics.org/tutorial

wget https://cairographics.org/cairo-tutorial.tar.gz

tar xzf cairo-tutorial.tar.gz

cd cairo-tutorial

make

cat README

IRC: irc.freenode.net #cairo Carl Worth Red Hat, Inc. linux.conf.au 2006-01-26 https://cairographics.org Jaggies Fuzzies Fireworks

Let application authors know there are options

Learn to use cairo—patch the applications

Write your own cairo-using applications

Various shell cairo programs #include <cairo.h> #include <cairo-xlib.h> int main (void) { Display *dpy = XOpenDisplay (0); Window w = XCreateSimpleWindow (dpy,RootWindow (dpy, 0), 0, 0, WIDTH, HEIGHT, 0, 0, WhitePixel (dpy, 0)); cairo_surface_t *surface = cairo_xlib_surface_create (dpy, w, DefaultVisual (dpy, DefaultScreen (dpy)), WIDTH, HEIGHT); XEvent ev; XSelectInput (dpy, w, ExposureMask); XMapWindow (dpy, w); while (XNextEvent (dpy, &ev) == 0) if (ev.type == Expose && !ev.xexpose.count) { cairo_t *cr = cairo_create (surface); draw (cr); cairo_destroy (cr); } } #include <gtk/gtk.h> static gboolean handle_expose (GtkWidget *widget, GdkEventExpose *event, gpointer data) { cairo_t *cr = gdk_cairo_create (widget->window); draw (cr); cairo_destroy (cr); return FALSE; } int main (int argc, char **argv) { GtkWidget *window, *drawing_area; gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_window_set_default_size (GTK_WINDOW (window), WIDTH, HEIGHT); drawing_area = gtk_drawing_area_new (); gtk_container_add (GTK_CONTAINER (window), drawing_area); g_signal_connect (drawing_area, "expose-event", G_CALLBACK (handle_expose), NULL); gtk_widget_show_all (window); gtk_main (); } #include <cairo.h> int main (void) { cairo_surface_t *surface; cairo_t *cr; surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, WIDTH, HEIGHT); cr = cairo_create (surface); draw (cr); cairo_surface_write_to_png (surface, "foo.png"); cairo_surface_destroy (surface); cairo_destroy (cr); return 0; } #include <cairo.h> #include <cairo-pdf.h> int main (void) { cairo_surface_t *surface; cairo_t *cr; surface = cairo_pdf_surface_create ("foo.pdf", WIDTH, HEIGHT); cr = cairo_create (surface); draw (cr); cairo_show_page (cr); cairo_surface_destroy (surface); cairo_destroy (cr); return 0; } #!/usr/bin/env python import gtk import cairo def expose (widget, event): cr = widget.window.cairo_create () draw (cr) win = gtk.Window () win.connect ('destroy', gtk.main_quit) win.set_default_size(WIDTH, HEIGHT) drawingarea = gtk.DrawingArea () win.add (drawingarea) drawingarea.connect ('expose_event', expose) win.show_all () gtk.main () #!/usr/bin/env python import cairo surface = cairo.ImageSurface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT) cr = cairo.Context (surface) draw (cr) surface.write_to_png ('foo.png') autoimport Cairo; cairo_t cr = new (WIDTH, HEIGHT); draw (cr);

C++ (cairomm)

Haskell (hscairo)

Java (CairoJava, cairo-java)

Common Lisp (cl-cairo)

Nickle (cairo-5c)

Objective Caml (cairo-ocaml)

perl (cairo-perl)

python (pycairo)

ruby (rcairo)

squeak (cairo-squeak)

https://cairographics.org/tutorial https://cairographics.org/cairo-tutorial.tar.gz

tar xzf cairo-tutorial.tar.gz

cd cairo-tutorial

make

cat README

IRC: irc.freenode.net #cairo Here comes the fun part

• Paths
• construction
• filling, stroking
• Images
• loading from disk
• using as source
• transforming/filtering
• Text
• “Toy” API
• “Full” API

• Paths
• cairo_stroke
• cairo_fill
• Images
• cairo_paint
• cairo_mask
• cairo_paint_with_alpha
• Text
• cairo_show_text (“toy”)
• cairo_show_glyphs (“full”)

• Paths consist of lines and splines:
• cairo_move_to
start new sub path, set current point
• cairo_line_to
add line segment to path
• cairo_curve_to
add Bézier spline to path
• cairo_close_path
add line segment to last move_to point

• cairo_stroke
• Paints the path itself as stroked by a pen
• Controlled by various stroke parameters:
• cairo_set_line_width
• cairo_set_line_cap
• cairo_set_line_join
• cairo_set_miter_limit
• cairo_set_dash

• CAIRO_LINE_CAP_BUTT
• CAIRO_LINE_CAP_ROUND
• CAIRO_LINE_CAP_SQUARE

• CAIRO_LINE_JOIN_BEVEL
• CAIRO_LINE_JOIN_ROUND
• CAIRO_LINE_JOIN_MITER

Adds a line segment (if necessary) to the

start of the path

Draws a join from that line to the first

element of the path

• Paints the “inside” of the path
• Two different ways to determine inside-ness
• cairo_set_fill_rule:
CAIRO_FILL_RULE_WINDING CAIRO_FILL_RULE_EVEN_ODD

To test a point for inside-ness, imagine a ray

from the point and extending to infinity (any direction) and examine path crossings

EVEN_ODD counts crossings and fills when odd

WINDING counts up/down for left/right crossings

and fills when the final number is not zero

All drawing occurs with the source pattern

Uniform-color sources can be set

with or without alpha:

• cairo_set_source_rgb
• cairo_set_source_rgba

cairo_stroke and cairo_fill consume the path

Variants are available to preserve the path:

• cairo_stroke_preserve
• cairo_fill_preserve

This is a variation from PostScript and PDF

• The cairo approach differs in different ways
• We think this way is better (of course)

• cairo_rectangle
• cairo_arc
• cairo_text_path
• cairo_glyph_path
• Relative-coordinate variants:
• cairo_rel_move_to
• cairo_rel_line_to
• cairo_rel_curve_to

• Single matrix combines rotation, translation,
scale and shear
• Non-projective transformations
• Pen doesn't change shape along the stroke
• Transformations are cumulative
• translate, scale != scale, translate

• cairo_save and cairo_restore
• Very useful for bracketing function bodies
• Eliminates graphics state side effects
• NOTE: Path is not part of graphics state
• Path is not affected by cairo_save/restore
• Useful for path-generating functions

cairo_clip

Intersects path with current clip to further

restrict drawing

Pixel-aligned clipping is much faster

cairo_clip_preserve is available as well

• Surface patterns
• Image from disk
• Results of cairo drawing
• Gradient patterns
• linear gradients
• radial gradients

• “Toy” API:
• Useful for demos like we are writing today
• No real layout—not useful for the majority
of writing systems in the world
• “Full” API:
• User must do OS-dependent font selection
• User must access font glyph IDs directly
• User must do all text layout

• Simple font selection
• family, weight, slant
• OS independent
• No font listing support
• UTF-8 text drawing and extents functions
• Still supports full font transformations

Just use pango

C has no exceptions

Checking each return is tedious

C programmers rarely bother

Lots of broken programs result

Cairo stores status value when error occurs

API “shuts down” when an error occurs

All cairo functions are benign

(and well defined) after any error.

cairo_status can be called when convenient

Error status values propagate across objects