Cairo 图形指南 (10) —— 文本

LiYanrui posted @ Apr 07, 2010 10:24:04 PM in 程序设计 with tags Cairo gtk , 10247 阅读

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。

#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)

 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。

 cairo_set_font_size(cr, 13);

这里设定字号。

 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。

#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[i], &extents);
      x += extents.width + 2;
      cairo_move_to(cr, x + 30, 50);
      cairo_show_text(cr, text[i]);  
  }

  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。

 gpointer text[7] = { "Z", "e", "t", "C", "o", "d", "e" };

构造一个字符数组。

 cairo_select_font_face(cr, "Courier",
    CAIRO_FONT_SLANT_NORMAL,
    CAIRO_FONT_WEIGHT_BOLD);

将字体设置为 Courier。

 for (i = 0; i < count; i++) {
    cairo_text_extents(cr, text[i], &extents);
    x += extents.width + 2;
    cairo_move_to(cr, x + 30, 50);
    cairo_show_text(cr, text[i]);  
 }

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。

#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。

 gint x = widget->allocation.width / 2;
 gint y = widget->allocation.height / 2;

获取窗口中心坐标。

 cairo_set_source_rgb(cr, 0.5, 0, 0); 
 cairo_paint(cr);

将背景设为暗红色。

 size += 0.8;

每轮循环,字号都增长 0.8 个单位。

 if (size > 20) {
     alpha -= 0.01;
 }

当字号大于 20 的时候,就开始淡出。

 cairo_text_extents(cr, "ZetCode", &extents);

获取文本尺寸。

 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。

 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。

 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)。


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