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docs: Drop the pre-1.0 porting guide
It's been nearly 20 years; time to let it go.
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Emmanuele Bassi
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265
PORTING_GUIDE
265
PORTING_GUIDE
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...-----=======-----...
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Cairo 1.0 Porting Guide
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...-----=======-----...
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Here are some notes on more easily porting cairo_code from cairo 0.4
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to cairo 1.0. It is sorted roughly in order of importance, (the items
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near the top are expected to affect the most people).
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Automated API renamings
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=======================
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There have been a lot of simple renamings where the functionality is
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the same but the name of the symbol is different. We have provided a
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script to automate the conversion of these symbols. It can be found
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within the cairo distribution in:
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util/cairo-api-update
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This script is used by installing it somewhere on your PATH, and the
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running it and providing the names of your source files on the command
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line. For example:
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cairo-api-update *.[ch]
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The script will first save backup copies of each file (renamed with a
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.bak extension) and then will perform all of the simple renamings.
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For your benefit, the script also produces messages giving filenames
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and line numbers for several of the manual API updates that you will
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need to perform as described below.
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Manual API changes
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==================
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This section of the porting guide describes changes you will have to
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manually make to your source code. In addition to the information in
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this guide, the cairo-api-update script will notify you of some of
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these issues as described above.
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Cairo's deprecation warnings
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----------------------------
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Also, if your compiler provides warnings for implicit declarations of
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functions, (eg. "gcc -Wall"), then simply attempting to compile your
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program will cause cairo to generate messages intended to guide you
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through the porting process.
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For example, if you neglect to update an old call to
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cairo_set_target_drawable, you might see an error message as follows:
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foo.c:10: warning: implicit declaration of function
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‘cairo_set_target_drawable_DEPRECATED_BY_cairo_xlib_surface_create’
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This message is indicating to you that the deprecatd function
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cairo_set_target_drawable appears in your program foo.c on line 10,
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and you should rewrite your program to call cairo_xlib_surface_create
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instead.
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The remainder of this porting guide is arranged as a set of common
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code patterns that appear in old (cairo-0.4) code and how it should be
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transformed to new (cairo-0.5) code.
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cairo_create
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------------
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Was: cr = cairo_create ();
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cairo_set_target_foo (cr, args);
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/* draw */
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cairo_destroy (cr);
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Now: cairo_surface_t *surface;
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surface = cairo_foo_surface_create (args);
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cr = cairo_create (surface);
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/* draw */
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cairo_destroy (cr);
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cairo_surface_destroy (surface);
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Or: cairo_surface_t *surface;
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surface = cairo_foo_surface_create (args);
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cr = cairo_create (surface);
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cairo_surface_destroy (surface);
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/* draw */
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cairo_destroy (cr);
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NOTE: Many of the cairo_foo_surface_create functions accept the
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identical arguments as the the old cairo_set_target_foo
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functions, (minus the cairo_t*), making this transformation
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quite easy. One notable exception is cairo_set_target_drawable
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which, when it becomes cairo_xlib_surface_create must pickup new
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arguments for the Visual*, the width, and the height.
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cairo_set_alpha (1)
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-------------------
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Was: cairo_set_rgb_color (cr, red, green, blue);
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cairo_set_alpha (cr, alpha);
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Now: cairo_set_source_rgba (cr, red, green, blue, alpha);
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cairo_show_surface
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------------------
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Was: cairo_show_surface (cr, surface, width, height);
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Now: cairo_set_source_surface (cr, surface, x, y);
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cairo_paint (cr);
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NOTE: The type signatures of cairo_show_surface and cairo_set_source
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are the same, but pay attention that cairo_show_surface required
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the width and height, while cairo_set_source_surface requires
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the X,Y location to where the surface will be placed.
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cairo_set_alpha (2)
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-------------------
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Was: cairo_set_alpha (cr, alpha);
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cairo_show_surface (cr, surface, width, height);
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Now: cairo_set_source_surface (cr, surface, x, y);
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cairo_paint_with_alpha (cr, alpha);
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filling and stroking
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--------------------
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Was: cairo_save (cr);
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/* set fill color */
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cairo_fiill (cr);
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cairo_restore (cr);
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/* set stroke color */
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cairo_stroke (cr);
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Now: /* set fill color */
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cairo_fill_preserve (cr);
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/* set stroke color */
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cairo_stroke (cr);
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NOTE: The current path is no longer saved/restored by
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cairo_save/cairo_restore. This can lead to some subtle
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surprises, so look out.
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cairo_matrix_t
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--------------
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Was: cairo_matrix_t *matrix;
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matrix = cairo_matrix_create ();
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/* Do stuff with matrix */
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cairo_matrix_destroy (matrix);
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Now: cairo_matrix_t matrix;
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cairo_matrix_init_identity (&matrix);
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/* Do stuff with &matrix */
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NOTE: If you are really lazy, you can still use a cairo_matrix_t* and
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avoid putting the &matrix all over by just replacing
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cairo_matrix_create() with malloc() and cairo_matrix_destroy()
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with free(). That's not as nice, and you still need to be
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careful to see if you need to initialize it to an identity
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matrix as cairo_matrix_create() did for you.
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Rendering to a temporary surface
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--------------------------------
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Was: cairo_save (cr);
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{
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cairo_set_target_surface (cr, temporary);
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/* draw through cr onto temporary */
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}
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cairo_restore (cr);
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/* use temporary as source on cr */
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Now: {
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cr2 = cairo_create (temporary);
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/* draw through cr2 onto temporary */
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cairo_destory (cr2);
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}
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/* use temporary as source on cr */
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NOTE: Having to create another cairo_t is a bit annoying, but having
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to invent a new name for it is just awful, (imagine a deeply
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nested version of this code). Fortunately, the style above is
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just a stop-gap measure until the new group API comes along.
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Iterating over a path
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---------------------
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Was: cairo_current_path (cr,
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my_move_to,
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my_line_to,
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my_curve_to,
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my_close_path,
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closure);
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Now: int i;
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cairo_path_t *path;
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cairo_path_data_t *data;
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path = cairo_copy_path (cr);
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for (i=0; i < path->num_data; i += path->data[i].header.length) {
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data = &path->data[i];
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switch (data->header.type) {
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case CAIRO_PATH_MOVE_TO:
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my_move_to (closure, data[1].point.x, data[1].point.y);
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break;
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case CAIRO_PATH_LINE_TO:
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my_line_to (closure, data[1].point.x, data[1].point.y);
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break;
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case CAIRO_PATH_CURVE_TO:
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my_curve_to (closure, data[1].point.x, data[1].point.y,
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data[2].point.x, data[2].point.y,
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data[3].point.x, data[3].point.y);
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break;
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case CAIRO_PATH_CLOSE_PATH:
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my_close_path (closure);
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break;
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}
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}
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cairo_path_destroy (path);
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NOTE: This version makes it looks like the new form is a _lot_ more
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verbose than the old version. But realize that the old version
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required the support of 4 additional functions. The new approach
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allows great flexibility including the ability to inline the
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entire operation within the switch statement when appropriate.
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Erasing a surface to transparent
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--------------------------------
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Was: cairo_set_rgb_color (cr, 0., 0., 0.);
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cairo_set_alpha (cr, 0.)
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cairo_set_operator (cr, CAIRO_OPERATOR_SRC);
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cairo_rectangle (cr, 0., 0., surface_width, surface_height);
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cairo_fill (cr);
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or: cairo_set_rgb_color (cr, 0., 0., 0.);
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cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
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cairo_rectangle (cr, 0., 0., surface_width, surface_height);
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cairo_fill (cr);
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Now: cairo_set_source_rgba (cr, 0., 0., 0., 0.);
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cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
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cairo_paint (cr);
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or: cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
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cairo_paint (cr);
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NOTE: Using cairo_rectangle and fill would still work just fine. It's
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just a lot more convenient to use cairo_paint now, (particularly
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as it doesn't require you to even know what the bounds of the
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target surface are).
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Drawing to a PNG file
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---------------------
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Was: file = fopen (filename, "w");
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cr = cairo_create ();
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cairo_set_target_png (cr, file, format, width, height);
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/* draw image */
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cairo_destroy (cr);
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fclose (file);
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Now: surface = cairo_image_surface_create (format, width, height);
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cr = cairo_create (surface);
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/* draw image */
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cairo_surface_write_to_png (surface, filename);
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cairo_destroy (cr);
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cairo_surface_destroy (surface);
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NOTE: The png backend is gone. So there is no cairo_png_surface_create
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to take the place of cairo_set_target_png. And notice that we
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used an image surface here, but it is just as easy to use
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cairo_surface_write_to_png with an xlib or other surface, (but
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not PDF at the moment). This is one of the big advantages of
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this approach as opposed to a PNG surface.
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