Add a simple legend

We're now not missing any features that the original motorsim plot had.

diff --git a/acre.c b/acre.c
index 12be71d249952421f0fb17caa956e3cd74377a0f..35d0541d9c4b14bc58eef0da4d86bc61121be27a 100644 (file)
--- a/acre.c
+++ b/acre.c
@@ -59,6 +59,8 @@ struct _acre {
     /* Data for drawing. */
     cairo_t *cr;
     PangoFontDescription *font;
+    struct { double r; double g; double b;} colors[3];
+    int num_colors;
 
     /* Total size including labels. */
     int width;
@@ -166,6 +168,8 @@ acre_add_data (acre_t *acre, acre_data_t *data)
 #define ACRE_TICK_MINOR_SIZE 3
 #define ACRE_X_TICK_VALUE_PAD 2
 #define ACRE_Y_TICK_VALUE_PAD 4
+#define ACRE_LEGEND_PAD 4
+#define ACRE_LEGEND_LINE_SIZE 10
 
 static PangoLayout *
 _create_layout (acre_t *acre, const char *text)
@@ -496,22 +500,32 @@ _compute_axis_ranges (acre_t *acre)
     cairo_restore (cr);
 }
 
+static void
+_choose_colors (acre_t *acre)
+{
+    /* XXX: Should choose N, equally-spaced colors from a perceptually
+     * linear space here. */
+    acre->num_colors = 3;
+
+    acre->colors[0].r = 1;
+    acre->colors[0].g = 0;
+    acre->colors[0].b = 0;
+
+    acre->colors[1].r = 0;
+    acre->colors[1].g = 1;
+    acre->colors[1].b = 0;
+
+    acre->colors[2].r = 0;
+    acre->colors[2].g = 0;
+    acre->colors[2].b = 1;
+}
+
 static void
 _draw_data (acre_t *acre)
 {
     cairo_t *cr = acre->cr;
     unsigned int d, i;
     acre_data_t *data;
-#define NUM_COLORS 3
-    struct {
-       double r;
-       double g;
-       double b;
-    } colors [NUM_COLORS] = {
-       {1, 0, 0},
-       {0, 1, 0},
-       {0, 0, 1}
-    };
 
     cairo_save (cr);
 
@@ -520,11 +534,11 @@ _draw_data (acre_t *acre)
     _set_transform_to_data_space (acre);
 
     for (d = 0; d < acre->num_data; d++) {
-       int color = d % NUM_COLORS;
+       int color = d % acre->num_colors;
        cairo_set_source_rgb (cr,
-                             colors[color].r,
-                             colors[color].g,
-                             colors[color].b);
+                             acre->colors[color].r,
+                             acre->colors[color].g,
+                             acre->colors[color].b);
        data = acre->data[d];
        cairo_new_path (cr);
        for (i = 0; i < data->num_points; i++) {
@@ -628,6 +642,63 @@ _draw_ticks (acre_t *acre,
     cairo_restore (cr);
 }
 
+static void
+_draw_legend (acre_t *acre)
+{
+    PangoLayout *layout;
+    int label_width, max_label_width = 0;
+    int width, height;
+    unsigned int i;
+    cairo_t *cr = acre->cr;
+
+    cairo_save (cr);
+
+    for (i = 0; i < acre->num_data; i++) {
+       layout = _create_layout (acre, acre->data[i]->name);
+       pango_layout_get_pixel_size (layout, &label_width, NULL);
+       _destroy_layout (layout);
+       if (label_width > max_label_width)
+           max_label_width = label_width;
+    }
+
+    width = ACRE_LEGEND_PAD + ACRE_LEGEND_LINE_SIZE + ACRE_LEGEND_PAD + 
+       max_label_width + ACRE_LEGEND_PAD;
+    height = ACRE_LEGEND_PAD +
+       acre->num_data * (ACRE_FONT_SIZE + ACRE_LEGEND_PAD);
+
+    cairo_translate (cr, acre->chart.x, acre->chart.y);
+
+    cairo_translate (cr,
+                    acre->chart.width - ACRE_LEGEND_PAD - width,
+                    ACRE_LEGEND_PAD);
+
+    cairo_rectangle (cr, -0.5, -0.5, width + 1.0, height + 1.0);
+    cairo_set_source_rgb (cr, 0, 0, 0);
+    cairo_set_line_width (cr, 1.0);
+    cairo_stroke (cr);
+
+    cairo_translate (cr, ACRE_LEGEND_PAD, ACRE_LEGEND_PAD);
+
+    for (i = 0; i < acre->num_data; i++) {
+       cairo_move_to (cr, 0, ACRE_FONT_SIZE / 2 + 0.5);
+       cairo_rel_line_to (cr, ACRE_LEGEND_LINE_SIZE, 0);
+       cairo_set_source_rgb (cr,
+                             acre->colors[i % acre->num_colors].r,
+                             acre->colors[i % acre->num_colors].g,
+                             acre->colors[i % acre->num_colors].b);
+       cairo_stroke (cr);
+
+       layout = _create_layout (acre, acre->data[i]->name);
+       cairo_move_to (cr, ACRE_LEGEND_LINE_SIZE + ACRE_LEGEND_PAD, 0);
+       cairo_set_source_rgb (cr, 0, 0, 0);
+       _show_layout (cr, layout);
+
+       cairo_translate (cr, 0, ACRE_LEGEND_PAD + ACRE_FONT_SIZE);
+    }
+
+    cairo_restore (cr);
+}
+
 static void
 _draw_frame_and_ticks (acre_t *acre)
 {
@@ -671,6 +742,8 @@ acre_draw (acre_t *acre, cairo_t *cr, int width, int height)
 
     cairo_set_source_rgb (cr, 1, 1, 1);
 
+    _choose_colors (acre);
+
     /* We compute the axis ranges before doing label layout so that we
      * can account for the width of the y-axis value labels. */
     _compute_axis_ranges (acre);
@@ -683,6 +756,9 @@ acre_draw (acre_t *acre, cairo_t *cr, int width, int height)
 
     _draw_data (acre);
 
+    if (acre->num_data > 1)
+       _draw_legend (acre);
+
     _draw_frame_and_ticks (acre);
 }