Add option to turn off bold in chart title font.

Added the LXW_EXPLICIT_FALSE variable to allow the default bold
property in chart title fonts to be turned off.

Closes #199

examples/chart.c

@@ -44,6 +44,12 @@ int main() {
     chart_add_series(chart, NULL, "Sheet1!$B$1:$B$5");
     chart_add_series(chart, NULL, "Sheet1!$C$1:$C$5");
 
+
+    lxw_chart_font font = {.bold = LXW_EXPLICIT_FALSE, .color = LXW_COLOR_BLUE};
+
+    chart_title_set_name(chart, "Year End Results");
+    chart_title_set_name_font(chart, &font);
+
     /* Insert the chart into the worksheet. */
     worksheet_insert_chart(worksheet, CELL("B7"), chart);
 

include/xlsxwriter/chart.h

@@ -3235,7 +3235,7 @@ void chart_title_set_name_range(lxw_chart *chart, const char *sheetname,
  * chart title:
  *
  * @code
- *     lxw_chart_font font = {.bold = LXW_TRUE, .color = LXW_COLOR_BLUE};
+ *     lxw_chart_font font = {.color = LXW_COLOR_BLUE};
  *
  *     chart_title_set_name(chart, "Year End Results");
  *     chart_title_set_name_font(chart, &font);
@@ -3243,6 +3243,20 @@ void chart_title_set_name_range(lxw_chart *chart, const char *sheetname,
  *
  * @image html chart_title_set_name_font.png
  *
+ * In Excel a chart title font is bold by default (as shown in the image
+ * above). To turn off bold in the font you cannot use #LXW_FALSE (0) since
+ * that is indistinguishable from an uninitialized value. Instead you should
+ * use #LXW_EXPLICIT_FALSE:
+ *
+ * @code
+ *     lxw_chart_font font = {.bold = LXW_EXPLICIT_FALSE, .color = LXW_COLOR_BLUE};
+ *
+ *     chart_title_set_name(chart, "Year End Results");
+ *     chart_title_set_name_font(chart, &font);
+ * @endcode
+ *
+ * @image html chart_title_set_name_font2.png
+ *
  * For more information see @ref chart_fonts.
  */
 void chart_title_set_name_font(lxw_chart *chart, lxw_chart_font *font);

include/xlsxwriter/common.h

@@ -50,7 +50,10 @@ enum lxw_boolean {
     /** False value. */
     LXW_FALSE,
     /** True value. */
-    LXW_TRUE
+    LXW_TRUE,
+    /** False value. Used to turn off a property that is default on, in order
+     *  to distinguish it from an uninitialized value. */
+    LXW_EXPLICIT_FALSE
 };
 
 /**

test/functional/src/test_chart_title03.c

@@ -0,0 +1,45 @@
+/*****************************************************************************
+ * Test cases for libxlsxwriter.
+ *
+ * Test to compare output against Excel files.
+ *
+ * Copyright 2014-2021, John McNamara, jmcnamara@cpan.org
+ *
+ */
+
+#include "xlsxwriter.h"
+
+int main() {
+
+    lxw_workbook  *workbook  = workbook_new("test_chart_title03.xlsx");
+    lxw_worksheet *worksheet = workbook_add_worksheet(workbook, NULL);
+    lxw_chart     *chart     = workbook_add_chart(workbook, LXW_CHART_COLUMN);
+
+    /* For testing, copy the randomly generated axis ids in the target file. */
+    chart->axis_id_1 = 93211648;
+    chart->axis_id_2 = 87847680;
+
+    uint8_t data[5][3] = {
+        {1, 2,  3},
+        {2, 4,  6},
+        {3, 6,  9},
+        {4, 8,  12},
+        {5, 10, 15}
+    };
+
+    int row, col;
+    for (row = 0; row < 5; row++)
+        for (col = 0; col < 3; col++)
+            worksheet_write_number(worksheet, row, col, data[row][col], NULL);
+
+    chart_add_series(chart, NULL, "=Sheet1!$A$1:$A$5");
+
+    lxw_chart_font font = {.bold = LXW_EXPLICIT_FALSE, .baseline = -1};
+
+    chart_title_set_name(chart, "Title!");
+    chart_title_set_name_font(chart, &font);
+
+    worksheet_insert_chart(worksheet, CELL("E9"), chart);
+
+    return workbook_close(workbook);
+}

test/functional/test_chart_title.py

@@ -19,3 +19,5 @@ class TestCompareXLSXFiles(base_test_class.XLSXBaseTest):
     def test_chart_title02(self):
         self.run_exe_test('test_chart_title02')
 
+    def test_chart_title03(self):
+        self.run_exe_test('test_chart_title03')