Added 'min' crossing option to chart axes.

Add option to set a chart crossing to 'min' as well as the existing
'max' option. The 'min' option isn't available in the Excel interface
but can be enabled via VBA.

include/xlsxwriter/chart.h

@@ -1072,6 +1072,7 @@ typedef struct lxw_chart_axis {
     uint8_t display_units_visible;
 
     uint8_t has_crossing;
+    uint8_t crossing_min;
     uint8_t crossing_max;
     double crossing;
 
@@ -2700,6 +2701,26 @@ void chart_axis_set_crossing(lxw_chart_axis *axis, double value);
  */
 void chart_axis_set_crossing_max(lxw_chart_axis *axis);
 
+/**
+ * @brief Set the opposite axis crossing position as the axis minimum.
+ *
+ * @param axis  A pointer to a chart #lxw_chart_axis object.
+ *
+ * Set the position that the opposite axis will cross as the axis minimum.
+ * The default axis crossing position is generally the axis minimum so this
+ * function can be used to reverse the location of the axes without reversing
+ * the number sequence:
+ *
+ * @code
+ *     chart_axis_set_crossing_min(chart->x_axis);
+ *     chart_axis_set_crossing_min(chart->y_axis);
+ * @endcode
+ *
+ * **Axis types**: This function is applicable to to all axes types.
+ *                 See @ref ww_charts_axes.
+ */
+void chart_axis_set_crossing_min(lxw_chart_axis *axis);
+
 /**
  * @brief Turn off/hide an axis.
  *

src/chart.c

@@ -3318,7 +3318,9 @@ _chart_write_crosses(lxw_chart *self, lxw_chart_axis *axis)
 
     LXW_INIT_ATTRIBUTES();
 
-    if (axis->crossing_max)
+    if (axis->crossing_min)
+        LXW_PUSH_ATTRIBUTES_STR("val", "min");
+    else if (axis->crossing_max)
         LXW_PUSH_ATTRIBUTES_STR("val", "max");
     else
         LXW_PUSH_ATTRIBUTES_STR("val", "autoZero");
@@ -4261,7 +4263,8 @@ _chart_write_cat_axis(lxw_chart *self)
     _chart_write_cross_axis(self, self->axis_id_2);
 
     /* Write the c:crosses element. */
-    if (!self->y_axis->has_crossing || self->y_axis->crossing_max)
+    if (!self->y_axis->has_crossing || self->y_axis->crossing_min
+        || self->y_axis->crossing_max)
         _chart_write_crosses(self, self->y_axis);
     else
         _chart_write_crosses_at(self, self->y_axis);
@@ -4342,7 +4345,8 @@ _chart_write_val_axis(lxw_chart *self)
     _chart_write_cross_axis(self, self->axis_id_1);
 
     /* Write the c:crosses element. */
-    if (!self->x_axis->has_crossing || self->x_axis->crossing_max)
+    if (!self->x_axis->has_crossing || self->x_axis->crossing_min
+        || self->x_axis->crossing_max)
         _chart_write_crosses(self, self->x_axis);
     else
         _chart_write_crosses_at(self, self->x_axis);
@@ -4420,7 +4424,8 @@ _chart_write_cat_val_axis(lxw_chart *self)
     _chart_write_cross_axis(self, self->axis_id_2);
 
     /* Write the c:crosses element. */
-    if (!self->y_axis->has_crossing || self->y_axis->crossing_max)
+    if (!self->y_axis->has_crossing || self->y_axis->crossing_min
+        || self->y_axis->crossing_max)
         _chart_write_crosses(self, self->y_axis);
     else
         _chart_write_crosses_at(self, self->y_axis);
@@ -6139,7 +6144,17 @@ chart_axis_set_crossing(lxw_chart_axis *axis, double value)
 }
 
 /*
- * Set the axis crossing position as the max possible value.
+ * Set the axis crossing position as the minimum possible value.
+ */
+void
+chart_axis_set_crossing_min(lxw_chart_axis *axis)
+{
+    axis->has_crossing = LXW_TRUE;
+    axis->crossing_min = LXW_TRUE;
+}
+
+/*
+ * Set the axis crossing position as the maximum possible value.
  */
 void
 chart_axis_set_crossing_max(lxw_chart_axis *axis)

test/functional/src/test_chart_crossing05.c

@@ -0,0 +1,44 @@
+/*****************************************************************************
+ * Test cases for libxlsxwriter.
+ *
+ * Test to compare output against Excel files.
+ *
+ * Copyright 2014-2020, John McNamara, jmcnamara@cpan.org
+ *
+ */
+
+#include "xlsxwriter.h"
+
+int main() {
+
+    lxw_workbook  *workbook  = workbook_new("test_chart_crossing05.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 = 55948032;
+    chart->axis_id_2 = 55950336;
+
+    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$5");
+    chart_add_series(chart, NULL, "=Sheet1!$B$1:$B$5");
+    chart_add_series(chart, NULL, "=Sheet1!$C$1:$C$5");
+
+    chart_axis_set_crossing_min(chart->x_axis);
+
+    worksheet_insert_chart(worksheet, CELL("E9"), chart);
+
+    return workbook_close(workbook);
+}

test/functional/src/test_chart_crossing06.c

@@ -0,0 +1,44 @@
+/*****************************************************************************
+ * Test cases for libxlsxwriter.
+ *
+ * Test to compare output against Excel files.
+ *
+ * Copyright 2014-2020, John McNamara, jmcnamara@cpan.org
+ *
+ */
+
+#include "xlsxwriter.h"
+
+int main() {
+
+    lxw_workbook  *workbook  = workbook_new("test_chart_crossing06.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 = 72794880;
+    chart->axis_id_2 = 72796416;
+
+    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$5");
+    chart_add_series(chart, NULL, "=Sheet1!$B$1:$B$5");
+    chart_add_series(chart, NULL, "=Sheet1!$C$1:$C$5");
+
+    chart_axis_set_crossing_min(chart->y_axis);
+
+    worksheet_insert_chart(worksheet, CELL("E9"), chart);
+
+    return workbook_close(workbook);
+}

test/functional/test_chart_crossing.py

@@ -24,3 +24,9 @@ class TestCompareXLSXFiles(base_test_class.XLSXBaseTest):
 
     def test_chart_crossing04(self):
         self.run_exe_test('test_chart_crossing04')
+
+    def test_chart_crossing05(self):
+        self.run_exe_test('test_chart_crossing05')
+
+    def test_chart_crossing06(self):
+        self.run_exe_test('test_chart_crossing06')