如何使用 gtk+ 用 cairo 重绘文本

Question

我正在使用 cairo 绘制一些圆形小部件，例如 this。

我使用"draw"绘图区事件绘制了所有的小部件，但我不知道如何更新小部件中的数据。这是我编写的代码：

gboolean hald_circular_gauge (GtkWidget *widget,cairo_t *cr, gdouble max, gdouble min, gdouble value, gchar *pcname ,gchar *unit){

cairo_text_extents_t extents, extentsTemp, extentsLabel, extentsTempMin, extentsTempMax;
  int width, height;
  gint percentage, linewidth;
  double x,y;
  gdouble declive = (360.0-180.0)/(max-min);
  gdouble origin = 180.0 - declive*min;
  gchar pcTemp[BUFSIZ];

  width = gtk_widget_get_allocated_width (widget);
  height = gtk_widget_get_allocated_height (widget);



  double angle1 = 180.0  * (M_PI/180.0);  /* angles are specified */
  double angle2 = 360.0 * (M_PI/180.0);  /* in radians           */

  if(min > value || value >max)
      return FALSE;

  linewidth = (MIN (width, height) / 2.0 * 30.0) / 100.0;

  cairo_set_source_rgba (cr, 1.0, 1.0, 1.0, 0.6);
  cairo_set_line_width (cr, linewidth);
  cairo_arc(cr, width/2.0, height/2.0,  MIN (width, height) / 2.0 - linewidth, angle1, angle2);
  cairo_stroke (cr);

  cairo_set_source_rgba (cr, 0.0, 0.9, 0.0, 1.0);
  cairo_set_line_width (cr, linewidth);
  cairo_arc(cr, width/2.0, height/2.0, MIN (width, height) / 2.0  - linewidth, 180.0  * (M_PI/180.0),(declive*value+origin)  * (M_PI/180.0) );
  cairo_stroke (cr);

  cairo_select_font_face (cr, "Roboto Thin", CAIRO_FONT_SLANT_NORMAL,
          CAIRO_FONT_WEIGHT_NORMAL);
  cairo_set_font_size (cr, linewidth);
  cairo_set_source_rgb (cr, 1.0, 1.0, 1);
  cairo_text_extents (cr, unit, &extents);
  x = width/2.0-(extents.width/2 + extents.x_bearing);
  y = height/2.0 - (extents.height/2 );
  cairo_move_to (cr, x, y);
  cairo_show_text (cr, unit);

  cairo_select_font_face (cr, "Roboto", CAIRO_FONT_SLANT_NORMAL,
              CAIRO_FONT_WEIGHT_BOLD);
  cairo_set_font_size (cr, linewidth*1.3);
  sprintf(pcTemp,"%.1f",value);
  cairo_text_extents (cr, pcTemp, &extentsTemp);
      x = width/2.0-(extentsTemp.width/2 + extentsTemp.x_bearing);
      y = height/2.0 - extentsTemp.y_bearing;
  cairo_move_to (cr, x, y);
  cairo_show_text (cr, pcTemp);

  cairo_select_font_face (cr, "Roboto Thin", CAIRO_FONT_SLANT_NORMAL,
                  CAIRO_FONT_WEIGHT_NORMAL);
  cairo_set_font_size (cr, linewidth);
  cairo_text_extents (cr, pcname, &extentsLabel);
      x = width/2.0-(extentsLabel.width/2 + extentsLabel.x_bearing);
      y = height/2.0 - extentsTemp.y_bearing  - extentsLabel.y_bearing*1.20;
  cairo_move_to (cr, x, y);
  cairo_show_text (cr, pcname);


  cairo_select_font_face (cr, "Roboto Thin", CAIRO_FONT_SLANT_NORMAL,
                      CAIRO_FONT_WEIGHT_NORMAL);
  cairo_set_font_size (cr, linewidth*0.5);
  sprintf(pcTemp,"%.1f",min);
  cairo_text_extents (cr, pcTemp, &extentsTempMin);
      x = width/2.0  - MIN (width, height) / 2.0 + linewidth - (extentsTempMin.width/2 + extentsTempMin.x_bearing);
      y = height/2.0 - extentsTempMin.y_bearing*1.20;
  cairo_move_to (cr, x, y);
  cairo_show_text (cr, pcTemp);


  cairo_select_font_face (cr, "Roboto Thin", CAIRO_FONT_SLANT_NORMAL,
                      CAIRO_FONT_WEIGHT_NORMAL);
      cairo_set_font_size (cr, linewidth*0.5);
      sprintf(pcTemp,"%.1f",max);
      cairo_text_extents (cr, pcTemp, &extentsTempMax);
          x = width/2.0  + MIN (width, height) / 2.0 - linewidth + (-extentsTempMax.width/2 + extentsTempMax.x_bearing);
          y = height/2.0 - extentsTempMax.y_bearing*1.20;
      cairo_move_to (cr, x, y);
      cairo_show_text (cr, pcTemp);
    return TRUE;
 }

结果是this

 GtkWidget *drawing_area = gtk_drawing_area_new ();
     gtk_widget_set_size_request (drawing_area, 100, 100);
     gtk_box_pack_start (GTK_BOX(gtk_builder_get_object(builder, "box30")),drawing_area,FALSE,TRUE,0);

我创建了一个绘图区并请求了尺寸，但我没有得到这个尺寸。所以我的问题是：

如何更新绘图区域内的数据（生成绘图事件？？）？
为什么我不能请求绘图区域小部件的大小？

欢迎提出意见。

Answer 1

回答

1) 每次更新数据时，强制绘制更新：

gtk_widget_queue_draw(GTK_WIDGET(drawing_area))

2) 您可以请求一个大小，但如果容器设置为展开，则小部件最终可以展开； set_size_request function/method 将设置绘图区域的最小尺寸 "have"。从您的代码中我们可以看到，绘图区域位于 GtkBox 内。检查展开和填充标志。

提示 1：您可以在 GtkFixed 容器中使用 drawing_area 来测试 set_size_request

提示 2：尝试创建一个自定义小部件，这将是一个更好的解决方案。

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