[转]Cairo 图形指南 (10) —— 文本

Tom · 发表于 2011-2-3 02:20:24

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, &quot

urisa",
   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, &quot

urisa",
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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1	cairo_set_font_size(cr, 13);

这里设定字号。
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1 2	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。

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[7] = { "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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1	gpointer text[7] = { "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。

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[7] = { "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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1 2	gint x = widget->allocation.width / 2; gint y = widget->allocation.height / 2;

获取窗口中心坐标。
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1 2	cairo_set_source_rgb(cr, 0.5, 0, 0); cairo_paint(cr);

将背景设为暗红色。
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1	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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1	cairo_text_extents(cr, "ZetCode", &extents);

获取文本尺寸。
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1	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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1 2	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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1 2	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）。

原文地址：http://liyanrui.is-programmer.com/2010/4/7/cairo-text.16643.html

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