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<svgslides
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<slides theme="cairo"
presentation="Drawing with cairo"
presentation-subtitle="drawing with cairo"
URL="http://cairographics.org"
bullet="bullet">
<slide title="Tutorial preparation" variant="blank" bullet="">
<lc></lc>
<lc align="center">http://cairographics.org/tutorial</lc>
<lc></lc>
<li>wget http://cairographics.org/cairo-tutorial.tar.gz</li>
<li>tar xzf cairo-tutorial.tar.gz</li>
<li>cd cairo-tutorial</li>
<li>make</li>
<li>cat README</li>
<lc></lc>
<lc align="center">IRC: irc.freenode.net #cairo</lc>
</slide>
<slide variant="title">
<lc>Carl Worth</lc>
<lc>Red Hat, Inc.</lc>
<lc></lc>
<lc>linux.conf.au</lc>
<lc>2006-01-26</lc>
<lc>http://cairographics.org</lc>
</slide>
<slide title="Ugly graphics" variant="separator">
<lc align="left">Jaggies</lc>
<lc align="center">Fuzzies</lc>
<lc align="right">Fireworks</lc>
</slide>
<slide title="Jaggies">
<img src="jaggies.svg"/>
</slide>
<slide title="Fuzzies">
<img src="fuzzies.svg"/>
</slide>
<slide title="Fireworks">
</slide>
<slide title="What you can do about it">
<li>Let application authors know there are options</li>
<li>Learn to use cairo—patch the applications</li>
<li>Write your own cairo-using applications</li>
</slide>
<slide title="Getting started" variant="separator">
<lc align="center">Various shell cairo programs</lc>
</slide>
<slide title="Minimal cairo-xlib program" variant="code">
<lc>#include &lt;cairo.h&gt;</lc>
<lc>#include &lt;cairo-xlib.h&gt;</lc>
<lc>int main (void) {</lc>
<lc> Display *dpy = XOpenDisplay (0);</lc>
<lc> Window w = XCreateSimpleWindow (dpy,RootWindow (dpy, 0),</lc>
<lc> 0, 0, WIDTH, HEIGHT, 0, 0, WhitePixel (dpy, 0));</lc>
<lc> cairo_surface_t *surface = cairo_xlib_surface_create (dpy, w,</lc>
<lc> DefaultVisual (dpy, DefaultScreen (dpy)),</lc>
<lc> WIDTH, HEIGHT);</lc>
<lc> XEvent ev;</lc>
<lc> XSelectInput (dpy, w, ExposureMask);</lc>
<lc> XMapWindow (dpy, w);</lc>
<lc> while (XNextEvent (dpy, &amp;ev) == 0)</lc>
<lc> if (ev.type == Expose &amp;&amp; !ev.xexpose.count) {</lc>
<lc> cairo_t *cr = cairo_create (surface);</lc>
<lc> draw (cr);</lc>
<lc> cairo_destroy (cr);</lc>
<lc> }</lc>
<lc>}</lc>
</slide>
<slide title="Minimal cairo-gtk program" variant="code">
<lc>#include &lt;gtk/gtk.h&gt;</lc>
<lc>static gboolean</lc>
<lc>handle_expose (GtkWidget *widget, GdkEventExpose *event, gpointer data) {</lc>
<lc> cairo_t *cr = gdk_cairo_create (widget->window);</lc>
<lc> draw (cr);</lc>
<lc> cairo_destroy (cr);</lc>
<lc> return FALSE;</lc>
<lc>}</lc>
<lc>int main (int argc, char **argv) {</lc>
<lc> GtkWidget *window, *drawing_area;</lc>
<lc> gtk_init (&amp;argc, &amp;argv);</lc>
<lc> window = gtk_window_new (GTK_WINDOW_TOPLEVEL);</lc>
<lc> gtk_window_set_default_size (GTK_WINDOW (window), WIDTH, HEIGHT);</lc>
<lc> drawing_area = gtk_drawing_area_new ();</lc>
<lc> gtk_container_add (GTK_CONTAINER (window), drawing_area);</lc>
<lc> g_signal_connect (drawing_area, "expose-event",</lc>
<lc> G_CALLBACK (handle_expose), NULL);</lc>
<lc> gtk_widget_show_all (window); gtk_main ();</lc>
<lc>}</lc>
</slide>
<slide title="Minimal cairo-png program" variant="code">
<lc>#include &lt;cairo.h&gt;</lc>
<lc></lc>
<lc>int main (void)</lc>
<lc>{</lc>
<lc> cairo_surface_t *surface;</lc>
<lc> cairo_t *cr;</lc>
<lc></lc>
<lc> surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,</lc>
<lc> WIDTH, HEIGHT);</lc>
<lc> cr = cairo_create (surface);</lc>
<lc> draw (cr);</lc>
<lc> cairo_surface_write_to_png (surface, "foo.png");</lc>
<lc></lc>
<lc> cairo_surface_destroy (surface);</lc>
<lc> cairo_destroy (cr);</lc>
<lc></lc>
<lc> return 0;</lc>
<lc>}</lc>
</slide>
<slide title="Minimal cairo-pdf program" variant="code">
<lc>#include &lt;cairo.h&gt;</lc>
<lc>#include &lt;cairo-pdf.h&gt;</lc>
<lc>int main (void)</lc>
<lc>{</lc>
<lc> cairo_surface_t *surface;</lc>
<lc> cairo_t *cr;</lc>
<lc></lc>
<lc> surface = cairo_pdf_surface_create ("foo.pdf", WIDTH, HEIGHT);</lc>
<lc> </lc>
<lc> cr = cairo_create (surface);</lc>
<lc> draw (cr);</lc>
<lc> cairo_show_page (cr);</lc>
<lc></lc>
<lc> cairo_surface_destroy (surface);</lc>
<lc> cairo_destroy (cr);</lc>
<lc></lc>
<lc> return 0;</lc>
<lc>}</lc>
</slide>
<slide title="Minimal pycairo-gtk shell" variant="code">
<lc>#!/usr/bin/env python</lc>
<lc>import gtk</lc>
<lc>import cairo</lc>
<lc></lc>
<lc>def expose (widget, event):</lc>
<lc> cr = widget.window.cairo_create ()</lc>
<lc> draw (cr)</lc>
<lc> </lc>
<lc>win = gtk.Window ()</lc>
<lc>win.connect ('destroy', gtk.main_quit)</lc>
<lc>win.set_default_size(WIDTH, HEIGHT)</lc>
<lc>drawingarea = gtk.DrawingArea ()</lc>
<lc>win.add (drawingarea)</lc>
<lc>drawingarea.connect ('expose_event', expose)</lc>
<lc>win.show_all ()</lc>
<lc>gtk.main ()</lc>
</slide>
<slide title="Minimal pycairo-png shell" variant="code">
<lc>#!/usr/bin/env python</lc>
<lc>import cairo</lc>
<lc></lc>
<lc>surface = cairo.ImageSurface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT)</lc>
<lc>cr = cairo.Context (surface)</lc>
<lc></lc>
<lc>draw (cr)</lc>
<lc></lc>
<lc>surface.write_to_png ('foo.png')</lc>
</slide>
<slide title="Minimal nickle program" variant="code">
<lc>autoimport Cairo;</lc>
<lc></lc>
<lc>cairo_t cr = new (WIDTH, HEIGHT);</lc>
<lc>draw (cr);</lc>
</slide>
<slide title="Available bindings:" variant="large-content">
<li>C++ (cairomm)</li>
<li>Haskell (hscairo)</li>
<li>Java (CairoJava, cairo-java)</li>
<li>Common Lisp (cl-cairo)</li>
<li>Nickle (cairo-5c)</li>
<li>Objective Caml (cairo-ocaml)</li>
<li>perl (cairo-perl)</li>
<li>python (pycairo)</li>
<li>ruby (rcairo)</li>
<li>squeak (cairo-squeak)</li>
</slide>
<slide title="Following along" >
<lc></lc>
<lc align="center">http://cairographics.org/tutorial</lc>
<lc align="center">http://cairographics.org/cairo-tutorial.tar.gz</lc>
<li>tar xzf cairo-tutorial.tar.gz</li>
<li>cd cairo-tutorial</li>
<li>make</li>
<li>cat README</li>
<lc align="center">IRC: irc.freenode.net #cairo</lc>
</slide>
<slide title="Cairo's rendering model">
<g>
<image x="0" y="0" xlink:href="rendering-model.png" width="800" height="500" />
</g>
</slide>
<slide title="Let's start drawing" variant="separator">
<lc align="center">Here comes the fun part</lc>
</slide>
<slide title="API Overview" variant="large-content">
<ul>
<li>Paths</li>
<ul>
<li>construction</li>
<li>filling, stroking</li>
</ul>
<li>Images</li>
<ul>
<li>loading from disk</li>
<li>using as source</li>
<li>transforming/filtering</li>
</ul>
<li>Text</li>
<ul>
<li>“Toy” API</li>
<li>“Full” API</li>
</ul>
</ul>
</slide>
<slide title="Drawing functions" variant="large-content">
<ul>
<li>Paths</li>
<ul>
<li>cairo_stroke</li>
<li>cairo_fill</li>
</ul>
<li>Images</li>
<ul>
<li>cairo_paint</li>
<li>cairo_mask</li>
<li>cairo_paint_with_alpha</li>
</ul>
<li>Text</li>
<ul>
<li>cairo_show_text (“toy”)</li>
<li>cairo_show_glyphs (“full”)</li>
</ul>
</ul>
</slide>
<slide title="Basic path building">
<ul>
<li>Paths consist of lines and splines:</li>
<ul>
<li>cairo_move_to</li>
<lc> start new sub path, set current point</lc>
<li>cairo_line_to</li>
<lc> add line segment to path</lc>
<li>cairo_curve_to</li>
<lc> add Bézier spline to path</lc>
<li>cairo_close_path</li>
<lc> add line segment to last move_to point</lc>
</ul>
</ul>
</slide>
<slide title="Stroking paths">
<ul>
<li>cairo_stroke</li>
<ul>
<li>Paints the path itself as stroked by a pen</li>
<li>Controlled by various stroke parameters:</li>
<ul>
<li>cairo_set_line_width</li>
<li>cairo_set_line_cap</li>
<li>cairo_set_line_join</li>
<li>cairo_set_miter_limit</li>
<li>cairo_set_dash</li>
</ul>
</ul>
</ul>
</slide>
<slide title="cairo_stroke example">
</slide>
<slide title="cairo_set_line_width">
</slide>
<slide title="cairo_set_line_cap example">
<ul>
<li>CAIRO_LINE_CAP_BUTT</li>
<li>CAIRO_LINE_CAP_ROUND</li>
<li>CAIRO_LINE_CAP_SQUARE</li>
</ul>
</slide>
<slide title="cairo_set_line_join example">
<ul>
<li>CAIRO_LINE_JOIN_BEVEL</li>
<li>CAIRO_LINE_JOIN_ROUND</li>
<li>CAIRO_LINE_JOIN_MITER</li>
</ul>
</slide>
<slide title="cairo_close_path example">
<li>Adds a line segment (if necessary) to the</li>
<lc>start of the path</lc>
<li>Draws a join from that line to the first</li>
<lc>element of the path</lc>
</slide>
<slide title="cairo_set_dash example">
</slide>
<slide title="cairo_fill">
<ul>
<li>Paints the “inside” of the path</li>
<li>Two different ways to determine inside-ness</li>
<ul>
<li>cairo_set_fill_rule:</li>
<lc> CAIRO_FILL_RULE_WINDING</lc>
<lc> CAIRO_FILL_RULE_EVEN_ODD</lc>
</ul>
</ul>
</slide>
<slide title="cairo_fill example">
</slide>
<slide title="cairo_set_fill_rule">
<li>To test a point for inside-ness, imagine a ray</li>
<lc>from the point and extending to infinity</lc>
<lc>(any direction) and examine path crossings</lc>
<li>EVEN_ODD counts crossings and fills when odd</li>
<li>WINDING counts up/down for left/right crossings</li>
<lc>and fills when the final number is not zero</lc>
</slide>
<slide title="Fill rule example">
</slide>
<slide title="Something besides black?">
<li>All drawing occurs with the source pattern</li>
<li>Uniform-color sources can be set</li>
<lc>with or without alpha:</lc>
<ul>
<li>cairo_set_source_rgb</li>
<li>cairo_set_source_rgba</li>
</ul>
</slide>
<slide title="cairo_set_source example">
</slide>
<slide title="Fill and stroke the same path">
<li>cairo_stroke and cairo_fill consume the path</li>
<li>Variants are available to preserve the path:</li>
<ul>
<li>cairo_stroke_preserve</li>
<li>cairo_fill_preserve</li>
</ul>
<li>This is a variation from PostScript and PDF</li>
<ul>
<li>The cairo approach differs in different ways</li>
<li>We think this way is better (of course)</li>
</ul>
</slide>
<slide title="Fill and stroke example">
</slide>
<slide title="More path building">
<ul>
<li>cairo_rectangle</li>
<li>cairo_arc</li>
<li>cairo_text_path</li>
<li>cairo_glyph_path</li>
<li>Relative-coordinate variants:</li>
<ul>
<li>cairo_rel_move_to</li>
<li>cairo_rel_line_to</li>
<li>cairo_rel_curve_to</li>
</ul>
</ul>
</slide>
<slide title="cairo_arc example">
</slide>
<slide title="Outline text">
</slide>
<slide title="Affine Transformations">
<ul>
<li>Single matrix combines rotation, translation,</li>
<lc>scale and shear</lc>
<li>Non-projective transformations</li>
<ul>
<li>Pen doesn't change shape along the stroke</li>
</ul>
<li>Transformations are cumulative</li>
<ul>
<li>translate, scale != scale, translate</li>
</ul>
</ul>
</slide>
<slide title="Affine Transform Example">
</slide>
<slide title="Save/Restore Graphics States">
<ul>
<li>cairo_save and cairo_restore</li>
<li>Very useful for bracketing function bodies</li>
<li>Eliminates graphics state side effects</li>
<lc></lc>
<li>NOTE: Path is not part of graphics state</li>
<ul>
<li>Path is not affected by cairo_save/restore</li>
<li>Useful for path-generating functions</li>
</ul>
</ul>
</slide>
<slide title="Clipping">
<li>cairo_clip</li>
<li>Intersects path with current clip to further</li>
<lc>restrict drawing</lc>
<li>Pixel-aligned clipping is much faster</li>
<li>cairo_clip_preserve is available as well</li>
</slide>
<slide title="Other source patterns">
<ul>
<li>Surface patterns</li>
<ul>
<li>Image from disk</li>
<li>Results of cairo drawing</li>
</ul>
<li>Gradient patterns</li>
<ul>
<li>linear gradients</li>
<li>radial gradients</li>
</ul>
</ul>
</slide>
<slide title="Loading an image file">
</slide>
<slide title="Painting an image">
</slide>
<slide title="Pattern transformation">
</slide>
<slide title="Pattern filtering">
</slide>
<slide title="Linear gradient example">
</slide>
<slide title="Radial gradient example">
</slide>
<slide title="Text">
<ul>
<li>“Toy” API:</li>
<ul>
<li>Useful for demos like we are writing today</li>
<li>No real layout—not useful for the majority</li>
<lc>of writing systems in the world</lc>
</ul>
<li>“Full” API:</li>
<ul>
<li>User must do OS-dependent font selection</li>
<li>User must access font glyph IDs directly</li>
<li>User must do all text layout</li>
</ul>
</ul>
</slide>
<slide title="“Toy” text API"/>
<ul>
<li>Simple font selection</li>
<ul>
<li>family, weight, slant</li>
<li>OS independent</li>
<li>No font listing support</li>
</ul>
<li>UTF-8 text drawing and extents functions</li>
<li>Still supports full font transformations</li>
</ul>
<slide title="“Toy” text example">
</slide>
<slide title="“Real” text example">
<li>Just use pango</li>
</slide>
<slide title="Error handling in C">
<li>C has no exceptions</li>
<li>Checking each return is tedious</li>
<li>C programmers rarely bother</li>
<li>Lots of broken programs result</li>
</slide>
<slide title="Cairo error handling">
<li>Cairo stores status value when error occurs</li>
<li>API “shuts down” when an error occurs</li>
<li>All cairo functions are benign</li>
<lc>(and well defined) after any error.</lc>
<li>cairo_status can be called when convenient</li>
<li>Error status values propagate across objects</li>
</slide>
<slide title="Cairo error example">
</slide>
</slides>
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