months start on correct first day of the month, no <time.h> needed

1 files changed, 53 insertions, 21 deletions

diff --git a/src/draw.c b/src/draw.c
index a79c8a8..931bf61 100644
--- a/src/draw.c
+++ b/src/draw.c
@@ -28,6 +28,7 @@ struct dimensions {
 
 
 // Fill entire background with current color 
+// Function name is changed for clarity
 int fill_bg(cairo_t *c) {
    cairo_paint(c);
    return 0;
@@ -36,6 +37,7 @@ int fill_bg(cairo_t *c) {
 
 
 // Draw text at a certain point.
+// Needn't be a string pointer, can be fixed array of chars
 // Creates and destroys layout within the scope of the function
 // Is that performant when looped over 365 operations?
 int draw_text (cairo_t *c, double x, double y, char *text) {
@@ -59,7 +61,7 @@ int draw_text (cairo_t *c, double x, double y, char *text) {
 
 
 
-// Calculate dimenions for one page and stores it into the dimensions struct
+// Calculate dimenions for one page and stores it in the dimensions struct
 int calculate_dimensions(double pw, double ph, struct dimensions *d) {
    // Percentage of page that should be margin
    double margin = 0.1 * pw;
@@ -76,6 +78,7 @@ int calculate_dimensions(double pw, double ph, struct dimensions *d) {
    // Height is based on how tall # of weeks are 
    double month_height = box_height * 6.0;
 
+   // Set items in struct to calculated values
    d->row_count = 6;
    d->column_count = 7;
    d->paper_width = pw;
@@ -117,35 +120,64 @@ int print_dimensions(struct dimensions *d) {
 
 
 // Draws one month using daybox sub-surface & context, main context, and dimension struct
-int draw_month (cairo_t *c, cairo_t *cd, cairo_surface_t *s, struct dimensions *d, int days_in_month) {
+int draw_month (cairo_t *c, cairo_t *cd, cairo_surface_t *s, struct dimensions *d, int days_in_month, int start_day) {
    double cursor_x = d->month_top_corner_x;
+   if (start_day != 0) cursor_x = cursor_x + (d->day_width * start_day);
+   printf("%d\n", start_day);
    double cursor_y = d->month_top_corner_y;
 
+   int current_day = start_day;
+
    int increment = 0;
 
    char str[20];
 
    for (int i = 0; i < d->row_count; i++) {
-      for (int k = 0; k < d->column_count; k++) {
-         if (increment < days_in_month) {
-            cairo_set_source_rgb (cd, 0.0, 0.0, 255.0);
-            cairo_paint(cd);
-            cairo_set_source_rgb (cd, 255.0, 255.0, 255.0);
-            snprintf(str, sizeof(str), "%d", increment + 1);
-            draw_text(cd, 4.0, 4.0, str);
-
-            cairo_set_source_surface (c, s, cursor_x, cursor_y);
-            cursor_x = cursor_x + d->day_width;
-            cairo_paint(c);
-            increment++;
-         } else {
-            return 0;
-         }
-      }
-
-      cursor_x = d->month_top_corner_x;
-      cursor_y = cursor_y + d->day_height;
+      for (int k = current_day; k < d->column_count; k++) {
+         // When the increment reached the end of the month, end
+         // the function.
+         if (increment >= days_in_month) return 0;
+
+         // Fill bg with color
+         cairo_set_source_rgb (cd, 0.0, 0.0, 255.0);
+         fill_bg(cd);
+
+         // Change text color
+         cairo_set_source_rgb (cd, 255.0, 255.0, 255.0);
+
+         // draw_text(), and by extension pango_layout_set_text(), needs a 
+         // string as input, so the current day's date is converted.
+         snprintf(str, sizeof(str), "%d", increment + 1);
+
+
+         // Position within cd is arbitrary: (0,0) is too close to edge
+         draw_text(cd, 4.0, 4.0, str);
+
+
+         // Position sub-surface on main surface
+         cairo_set_source_surface (c, s, cursor_x, cursor_y);
+         cairo_paint(c);
+
+         // Move cursor one box over 
+         cursor_x = cursor_x + d->day_width;
+         increment++;
+      } 
+      current_day = 0;
+   
+
+   cursor_x = d->month_top_corner_x;
+   cursor_y = cursor_y + d->day_height;
    }
+
    cairo_stroke(cd);
    return 0;
 }
+
+// Get the day of the week for a given day
+// Mostly used for calculating when the start of a month is
+// Relative to "Su Mo ... Sa" frame, not when Su and Sa are together
+// Range is 0 -> 6
+// https://wiki.c2.com/?PerpetualCalendarAlgorithm
+int day_of_week (int d, int m, int y) {
+   return((d += m < 3 ? y-- : y - 2, 23*m/9 + d + 4 + y/4- y/100 + y/400)%7);
+}