[PATCH 04/16] display_columns: add COL_DENSE to do unequal column layout

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

shrink_columns() calculate column width just enough to contain
text and padding.

relayout() uses shrink_columns() to try adding more columns after
columns are shrunk. However it only try that once.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 column.c |   70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 column.h |    1 +
 2 files changed, 71 insertions(+), 0 deletions(-)

diff --git a/column.c b/column.c
index d6e2d70..e7facf4 100644
--- a/column.c
+++ b/column.c
@@ -54,6 +54,68 @@ static void layout(const struct string_list *list,
 	*rows = DIV_ROUND_UP(list->nr, *cols);
 }
 
+/*
+ * Tighten columns just wide enough to fit its data and padding
+ * Return number of chars saved after shrinking.
+ */
+static int shrink_columns(const struct string_list *list, int mode,
+			   int *width, int padding, int rows, int cols)
+{
+	int x, y, i, len, item_len, spare = 0;
+	const char *s;
+
+	for (x = 0; x < cols; x++) {
+		for (y = len = 0; y < rows; y++) {
+			i = XY2SCALAR(mode, x, y, cols, rows);
+			if (i >= list->nr)
+				break;
+			s = list->items[i].string;
+			item_len = item_length(list, mode, s);
+			if (len < item_len)
+				len = item_len;
+		}
+		len += padding;
+
+		assert(len <= width[x]);
+		spare += width[x] - len;
+		width[x] = len;
+	}
+	return spare;
+}
+
+/* Try to tighten the layout and see if more columns can be added.*/
+static void relayout(const struct string_list *list,
+		     int mode, int original_width, int padding, int spare,
+		     int *initial_width, int **width, int *rows, int *cols)
+{
+	int new_rows, new_cols, new_initial_width;
+	int i, *new_width, new_spare, total_width;
+
+	/*
+	 * Assume all columns have same width, we would need
+	 * initial_width*cols. But then after shrinking, we have
+	 * "spare" more chars. Assume a new total_width with
+	 * additional chars, then re-shrink to see if it fits
+	 * c->width.
+	 */
+	total_width = (*initial_width)*(*cols) + spare;
+	layout(list, mode, total_width, padding,
+	       &new_initial_width, &new_rows, &new_cols);
+	new_width = xmalloc(sizeof(*new_width) * new_cols);
+	for (i = 0; i < new_cols; i++)
+		new_width[i] = new_initial_width;
+	new_spare = shrink_columns(list, mode, new_width, padding, new_rows, new_cols);
+
+	/* Does it fit? */
+	if (total_width - new_spare < original_width) {
+		free(*width);
+		*width = new_width;
+		*initial_width = new_initial_width;
+		*rows = new_rows;
+		*cols = new_cols;
+	}
+}
+
 /* Display without layout, COL_MODE_PLAIN */
 static void display_plain(const struct string_list *list, const char *indent)
 {
@@ -103,6 +165,14 @@ static void display_table(const struct string_list *list,
 	for (i = 0; i < cols; i++)
 		width[i] = initial_width;
 
+	if (mode & COL_DENSE) {
+		int spare = shrink_columns(list, mode, width, padding, rows, cols);
+		/* is it worth relayout? */
+		if (spare >= initial_width/2)
+			relayout(list, mode, total_width, padding, spare,
+				 &initial_width, &width, &rows, &cols);
+	}
+
 	empty_cell = xmalloc(initial_width + 1);
 	memset(empty_cell, ' ', initial_width);
 	empty_cell[initial_width] = '\0';
diff --git a/column.h b/column.h
index 3ed5731..cef354d 100644
--- a/column.h
+++ b/column.h
@@ -6,6 +6,7 @@
 #define COL_MODE_COLUMN        1   /* Fill columns before rows */
 #define COL_MODE_ROW           2   /* Fill rows before columns */
 #define COL_ANSI         (1 << 4) /* Remove ANSI escapes from string length */
+#define COL_DENSE        (1 << 5) /* Shrink columns when possible, making space for more columns */
 
 extern int term_columns(void);
 extern void display_columns(const struct string_list *list, int mode, int width, int padding, const char *indent);
-- 
1.7.2.2