[转]Cairo 图形指南 (10) —— 文本
本篇讲述如何处理文本。
灵魂伙伴
第一个示例是在 GTK+ 窗口中显示《灵魂伙伴》的部分歌词。
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#include <cairo.h>
#include <gtk/gtk.h>
static gboolean
on_expose_event(GtkWidget *widget,
GdkEventExpose *event,
gpointer data)
{
cairo_t *cr;
cr = gdk_cairo_create(widget->window);
cairo_set_source_rgb(cr, 0.1, 0.1, 0.1);
cairo_select_font_face(cr, "Purisa",
CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_BOLD);
cairo_set_font_size(cr, 13);
cairo_move_to(cr, 20, 30);
cairo_show_text(cr, "Most relationships seem so transitory");
cairo_move_to(cr, 20, 60);
cairo_show_text(cr, "They're all good but not the permanent one");
cairo_move_to(cr, 20, 120);
cairo_show_text(cr, "Who doesn't long for someone to hold");
cairo_move_to(cr, 20, 150);
cairo_show_text(cr, "Who knows how to love you without being told");
cairo_move_to(cr, 20, 180);
cairo_show_text(cr, "Somebody tell me why I'm on my own");
cairo_move_to(cr, 20, 210);
cairo_show_text(cr, "If there's a soulmate for everyone");
cairo_destroy(cr);
return FALSE;
}
int main (int argc, char *argv[])
{
GtkWidget *window;
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(window, "expose-event",
G_CALLBACK(on_expose_event), NULL);
g_signal_connect(window, "destroy",
G_CALLBACK(gtk_main_quit), NULL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 420, 250);
gtk_window_set_title(GTK_WINDOW(window), "Soulmate");
gtk_widget_set_app_paintable(window, TRUE);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
在这个示例中，显示了 Natasha Bedingfield 的《灵魂伙伴》的部分歌词。（在这里，可以听这首歌，很美妙）
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cairo_select_font_face(cr, "Purisa",
CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_BOLD);
这里设置字体。这个函数接受了三个字体参数的传入，字体的名称、样式与轻重。
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cairo_set_font_size(cr, 13);
这里设定字号。
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cairo_move_to(cr, 20, 30);
cairo_show_text(cr, "Most relationships seem so transitory");
通过在窗口中指定位置并调用 cairo_show_text() 函数显示文本。
http://zetcode.com/tutorials/cairographicstutorial/images/soulmate.png
一个字接一个字……
这种效果就是一个字一个字的显示，这些字的绘制存有时间差。
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#include <cairo.h>
#include <gtk/gtk.h>
gpointer text = { "Z", "e", "t", "C", "o", "d", "e" };
gboolean timer = TRUE;
static gboolean
on_expose_event(GtkWidget *widget,
GdkEventExpose *event,
gpointer data)
{
cairo_t *cr;
cairo_text_extents_t extents;
static gint count = 0;
cr = gdk_cairo_create(widget->window);
cairo_select_font_face(cr, "Courier",
CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_BOLD);
cairo_set_font_size(cr, 35);
cairo_set_source_rgb(cr, 0.2, 0.2, 0.2);
gint i;
gint x = 0;
for (i = 0; i < count; i++) {
cairo_text_extents(cr, text, &extents);
x += extents.width + 2;
cairo_move_to(cr, x + 30, 50);
cairo_show_text(cr, text);
}
count++;
if (count == 8) {
timer = FALSE;
count = 0;
}
cairo_destroy(cr);
return FALSE;
}
static gboolean
time_handler (GtkWidget *widget)
{
if (widget->window == NULL) return FALSE;
if (!timer) return FALSE;
gtk_widget_queue_draw(widget);
return TRUE;
}
int main (int argc, char *argv[])
{
GtkWidget *window;
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(window, "expose-event",
G_CALLBACK(on_expose_event), NULL);
g_signal_connect(window, "destroy",
G_CALLBACK(gtk_main_quit), NULL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 300, 90);
gtk_window_set_title(GTK_WINDOW(window), "ZetCode");
gtk_widget_set_app_paintable(window, TRUE);
g_timeout_add(1000, (GSourceFunc) time_handler, (gpointer) window);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
在这个示例中，我们在 GTK+ 窗口中画了“ZetCode”这个字串，并让逐个字母伴随一定的时间差逐一显示。
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gpointer text = { "Z", "e", "t", "C", "o", "d", "e" };
构造一个字符数组。
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cairo_select_font_face(cr, "Courier",
CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_BOLD);
将字体设置为 Courier。
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for (i = 0; i < count; i++) {
cairo_text_extents(cr, text, &extents);
x += extents.width + 2;
cairo_move_to(cr, x + 30, 50);
cairo_show_text(cr, text);
}
开始逐个字的绘制。extents.width 给出了当前字符的宽度。
http://zetcode.com/tutorials/cairographicstutorial/images/zetcode.gif
膨胀
下面这个示例中，我们制造了一种膨胀的效果。这个示例显示了一串在膨胀的居中文本，并且伴有淡出现象。这是很常见的效果，在 flash 动画里经常见到。
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#include <cairo.h>
#include <gtk/gtk.h>
gpointer text = { "Z", "e", "t", "C", "o", "d", "e" };
gboolean timer = TRUE;
static gboolean
on_expose_event(GtkWidget *widget,
GdkEventExpose *event,
gpointer data)
{
cairo_t *cr;
cairo_text_extents_t extents;
static gdouble alpha = 1.0;
static gdouble size = 1;
gint x = widget->allocation.width / 2;
gint y = widget->allocation.height / 2;
cr = gdk_cairo_create(widget->window);
cairo_set_source_rgb(cr, 0.5, 0, 0);
cairo_paint(cr);
cairo_select_font_face(cr, "Courier",
CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_BOLD);
size += 0.8;
if (size > 20) {
alpha -= 0.01;
}
cairo_set_font_size(cr, size);
cairo_set_source_rgb(cr, 1, 1, 1);
cairo_text_extents(cr, "ZetCode", &extents);
cairo_move_to(cr, x - extents.width/2, y);
cairo_text_path(cr, "ZetCode");
cairo_clip(cr);
cairo_stroke(cr);
cairo_paint_with_alpha(cr, alpha);
if (alpha <= 0) {
timer = FALSE;
}
cairo_destroy(cr);
return FALSE;
}
static gboolean
time_handler (GtkWidget *widget)
{
if (widget->window == NULL) return FALSE;
if (!timer) return FALSE;
gtk_widget_queue_draw(widget);
return TRUE;
}
int main (int argc, char *argv[])
{
GtkWidget *window;
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(window, "expose-event",
G_CALLBACK(on_expose_event), NULL);
g_signal_connect(window, "destroy",
G_CALLBACK(gtk_main_quit), NULL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 350, 200);
gtk_window_set_title(GTK_WINDOW(window), "puff");
gtk_widget_set_app_paintable(window, TRUE);
g_timeout_add(14, (GSourceFunc) time_handler, (gpointer) window);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
这个示例在 GTK+ 窗口中制造了一种膨胀并且淡出的文本渲染效果。
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gint x = widget->allocation.width / 2;
gint y = widget->allocation.height / 2;
获取窗口中心坐标。
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cairo_set_source_rgb(cr, 0.5, 0, 0);
cairo_paint(cr);
将背景设为暗红色。
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size += 0.8;
每轮循环，字号都增长 0.8 个单位。
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if (size > 20) {
alpha -= 0.01;
}
当字号大于 20 的时候，就开始淡出。
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cairo_text_extents(cr, "ZetCode", &extents);
获取文本尺寸。
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cairo_move_to(cr, x - extents.width/2, y);
根据文本尺寸来将文本定位在窗口的中心位置。
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cairo_text_path(cr, "ZetCode");
cairo_clip(cr);
获取文本的的路径，并将其设为当前的裁剪域。
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cairo_stroke(cr);
cairo_paint_with_alpha(cr, alpha);
绘制当前的路径，并为之添加 alpha 值（可实现淡出效果）。
http://zetcode.com/tutorials/cairographicstutorial/images/puff.gif
原文地址：http://liyanrui.is-programmer.com/2010/4/7/cairo-text.16643.html
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